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REFERENCES

1. Burgoon, D. A., Chang, O. C., Francini, R. B., Leis, B. N., and Rust, S. W., “Determining The Yield Stress of In-Service Pipe”, for ASME Gas Pipeline Safety Research Committee, Battelle, December, 1999 and published by ASME as CRTD Vol. 57.

2. O’Neill, H., “Hardness Measurement of Metals and Alloys,” Second Edition, Chapman and Hall Ltd, 1967.

3. Tabor, D., “The Hardness of Metals,” Oxford University Press, UK, 1951 (Reprinted by Redwood Books Ltd, UK).

4. Boklen, R., “A Simple Method for Obtaining the Ductility From a 100o-Cone Impression,” The Science of Hardness Testing And Its Research Applications, Chapter 8, American Society for Metals, 1973.

5. Boyer, H. E., ed.; “Hardness Testing,” ASM International, 1987. 6. Mott, B. W., “Micro-Indentation Hardness Testing,” Butterworths Scientific Publications,

London, 1956. 7. Small, L., “Hardness – Theory and Practice – Part 1 Practice,” Service Diamond Tool Co.,

Ferndale, MI., 1960. 8. Revankar, G., “Hardness Testing,” in ASM Handbook Volume 8, Mechanical Testing and

Evaluation, ASM International, 2000. 9. Anon, Wilson-Instron portable hardness tester data sheet. 10. Leeb, D., “Definition of the hardness value “L” in the Equotip dynamic measuring method,”

VDI Berichte Nr. 583, 1986/406. 11. Leeb, D., “Dynamic hardness testing of metallic materials,” NDT International, December

1979, pp. 274-278. 12. Private communication, Teleweld Corp, February 2008. 13. Anon, “Advanced Indentation System 3000,” www.fronticswest.com. 14. Prakash, R. V. and Shin, C. S., “An Evaluation of Stress Strain Property Prediction by

Automated Ball Indentation (ABI) Testing,” Journal of Testing and Evaluation, Vol. 35, No. 3, ASTM, 2007.

15. Choi, Y., et. al.; “Applications of Advanced Indentation Technique to Pre-Qualification and Periodic Monitoring of Strength Performance of Industrial Structures,” Key Engineering Materials, Trans Tech Publications, 2004.

16. Ahn, J-H. and Kwon, D., “Derivation of Plastic Stress-strain Relationship from Ball Indentions: Examination of Strain Definition and Pileup Effect,” Journal of Materials Research, Vol. 16, No. 11, November 2001, Materials Research Society.

17. Frank, S., “Mobile Hardness Testing – Application Guide for Hardness Testers,” GE Inspection Technologies.

18. Borggreen, K. and Auerkari, P., “Performance of some portable hardness testers,” 1999. 19. Sommer, J., “The Possibilities of Mobile Hardness Testing – A User Related Hardness

Testing Comparison of the Static UCI Method and the Dynamic Rebound Method,” October 1998, Vol. 3, No. 10, www.NDT.net.

20. Frank, S., “Portable Hardness Testing – Principles and Applications,” October 2002, Vol. 7, No. 10, www.NDT.net.

21. Anon, Krautkramer MIC 10 Portable Hardness Tester product literature, www.krautkramer.com.

22. Anon, Sonohard Ultrasonic Hardness Tester product literature, Microphotonics, www.microphotonics.com.

Downloaded From: http://ebooks.asmedigitalcollection.asme.org/pdfaccess.ashx?url=/data/books/802915/ on 07/10/2018 Terms of Use: http://www.asme.org/about-asme/terms-of-use

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23. Anon, Ernst Portable Hardness Tester product literature; www.ernstsa.com. 24. Anon, Equostat Hardness Tester product literature; www.proceq.com. 25. Boyer, H. E., ed., “Hardness Testing,” ASM International, Metals Park, OH, 1987. 26. Fultz, J., “Hard and Fast Rules for Portable Hardness Testing,” Inspection Trends,

www.aws.org. 27. Frank, S., “Portable Hardness Testing—Principles and Applications,” www.ndt.net. 28. Frank, S., “TIV (Through Indenter Viewing) New Possibilities of Mobile Hardness Testing,”

www.ndt.net. 29. Anon, “Krautkramer TIV Optical Hardness Tester- Mobile and Direct,”

www.GEInspectionTechnologies.com. 30. Shlegel, V. et. al., “The Use of MET-UD Combined Portable Hardness Testers For

Technological Control,” Centre for Physical and Mechanical Measurements, FSU, 2006. 31. Borggreen, K. and Auerkari, P., “Performance of some portable hardness testers.” Paper

authors are Swedish and Finnish. No additional details available. 32. Anon, Krautkramer MIC 10 Portable Hardness Tester product literature,

www.krautkramer.com. 33. Nelson, P.R., Coffin, M., Copeland, K.A.F., “Introductory Statistics for Engineering

Experimentation,” Elsevier Academic Press, 2003. 34. Bhattacharyya, G.K., Johnson, R.A., “Statistical Concepts and Methods,” John Wiley &

Sons, 1977. 35. Anon, “Guidelines on the Estimation of Uncertainty in Hardness Measurements,” European

Association of National Metrology Institutes (EURAMET), EURAMET/cg-16/v.01, July 2007.

36. Low, S. R., “Rockwell Hardness Measurement of Metallic Materials,” NIST Recommended Practice Guide, Special Publication 960-5, National Institute of Standards and Technology, January 2001.

37. Brice, L., Davis, F., and Crawshaw, A., “Uncertainty in Hardness Measurement,” NPL Report CMAM 87, National Physics Laboratory, UK, April 2003.

38. Polzin, T., “Determination of Uncertainty for Hardness Measurement: Proposal of the Standard, Available Software,” Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement, Springer. Volume 8, Number 12, December 2003.

39. Adams, T. M., “G104-A2LA Guide for Estimation of Measurement Uncertainty In Testing,” July 2002.

40. ASM Metals Handbook, Volume 8. 41. Auerkari, P., “On the Correlation of Hardness with Tensile and Yield Strength,” Technical

Research Center of Finland, Research Report 416, July 1986.


A-1

APPENDIX A Yield Strength from Hardness – Additional Background

This Appendix provides additional details pertaining to relationships that have been established that allow yield strength predictions from hardness measurements. In addition to the basic concepts covered in Section 3 of this Guide, other specific applications and methods that have been described in the literature are included below. Source A: The Welding Institute (UK). In 1975, The Welding Institute (UK) published data showing the relationship of Vickers hardness test results and yield strengths for weld metals, heat affected zones, and base metals. Data was collected that covered a wide range of steel types over a period of time. Their primary motivation was to develop hardness-yield strength correlations that could be used to estimate the yield strength in areas such as weld metals and heat affected zones where input for maximum defect size calculations could be simply obtained without the need to produce coupons suitable for tensile testing. Yield strength estimates from hardness testing of base metals were also considered to be useful where rapid evaluations were required. Figure A-1 illustrates the relationship between Vickers hardness (HV) and yield strength (ksi) for base metal including the 95% confidence limits. The original graph included higher strength materials that were outside the scope of the steels of interest in this Guide. Although a wide range of materials were represented, the relationship indicated in Figure A-1 suggests a reasonable correlation was still obtained.

Figure A-1. TWI Yield Strength – Hardness Relationship Source B: Hart, P. H. M., “Yield Strength from Hardness Data,” The Welding Institute Research Bulletin, June 1975, p 176. In 1978, additional yield strength-hardness data developed by The Welding Institute was added and the prior correlation was re-evaluated for two pass and multi-pass welds. This revised

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A-2

correlation was considered to improve yield strength predictions especially, for lower strength materials. Source C: Pargeter, R. J., “Yield Strength from Hardness-A Reappraisal For Weld Metal,” The Welding Institute Research Bulletin, November 1978, pp 325-326. Hardness-yield strength correlations were applied in 1966 to determine rolling schedules for sheet or strip. Yield strengths were required over a range of reductions that could be obtained by typical tensile or compression testing. A method was derived that allowed Vickers hardness test indentation estimates of compressive yield strength as alternative estimation method on rolled samples. The methodology was validated for a range of alloys including copper, aluminum, and other materials and compared well with tensile and plane compression test data. The accuracy achieved was considered to be sufficient to allow hardness testing in lieu of tensile/compression testing and also served as a quality control tool. Source D: Oliver, B. R. and Bowers, J. E., “The Determination of Yield Stress from Hardness Measurements,” Journal of the Institute of Metals, 1966, pp 223-225. A field evaluation of the hardness–yield strength relationship of high strength, quenched and tempered downhole tubular materials was conducted in the 1990’s. In this application, a portable Brinell tester was used to develop a relationship from tests conducted on API Grades C75 through V140 materials. Even though the tubular yield strength could be predicted within a ± 10,000 psi range, it was found that the prediction was sufficient to identify tubulars that failed due to low strengths and those that had been improperly heat treated resulting in low strength levels. Source E: Fehr, G. and Long, R., “Determining Metal Yield Strength in the Field,” ASME PD-Vol. 56, Drilling Technology, 1994. The objective of this work was to establish a relationship between the 0.2% offset yield strength of a material and the Vickers hardness and also consider the strain hardening coefficient. The methodology was derived from earlier work and relationships developed by Tabor and Meyer(3)

from analyses were conducted on an aluminum alloy and 1040 steel. A correlation was developed between the experimental yield strength (σy) and the value determined from the following expression resulting from this work:

2my B

3H −=σ

where: H = Vickers hardness

B = Constant (0.1 for steel) m = Meyer’s hardness coefficient n = strain hardening coefficient (=m-2)

Comparison of the yield strengths estimated using the above equation with experimental tensile data showed a good correlation was achieved. The validity of the equation was also evaluated


A-3

versus unknown aluminum, brass and steel tensile data. Good agreement between the above equation and the tensile data was achieved for all three materials. Source F: Cahoon, J. R., Broughton, W. H., and Kutzak, A. R., “The Determination of Yield Strength From Hardness Measurements”, ASME Intl, Metallurgical Transactions, Volume 2, July 1971. An automotive sheet metal application prompted the development of a hardness based yield strength estimation method for in-process material evaluations prior to and after forming operations. This method made use of the earlier relationships developed by Tabor and Meyer in addition to the results attributed by Cahoon that are described in the previous paragraph. A series of nomographs was constructed to permit yield strength measurements from the results of three Rockwell hardness tests conducted at different loads (i.e., HRF, HRB, HRG). Source G: George, R. A., Dinda, S., and Kasper, A. S., “Estimating Yield Strength From Hardness Data”, Metals Progress, ASM International, May 1976. This project was primarily an application of earlier work done by Tabor and the methodology reported by Cahoon (see synopsis F above). In this case, some modifications of Cahoon’s work were suggested and difficulties with estimating the strain hardening coefficient (n) were also reported. It was concluded that a reasonable estimate of both yield and tensile strength could be obtained from the Vickers hardness if “n” is known or can be determined. Source H: Auerkari, P., “On the Correlation of Hardness with Tensile and Yield Strength,” Technical Research Center of Finland, Research Report 416, July 1986. This work considered the relation between hardness and strength properties of metals was reviewed and compared with experimental data. It was found that the methods proposed by Cahoon resulted in a good correlation with tensile strength and provided a reasonable correlation with yield strength provided the strain hardening exponent (n) remains essentially constant. It was concluded that the available expressions correlating hardness with yield and tensile strength are very useful. Figure A-2 illustrates a yield strength hardness relationship developed from experimental data.


A-4

Figure A-2. Hardness–Yield Strength Relationship (From Auerkari)


B-1

APPENDIX B Field Hardness Tester -- Detailed Information

This Appendix provides additional details concerning the design and operational criteria necessary to properly select and apply the portable hardness testers covered in this Guide. All references in this Appendix refer to the Guide main body reference list. B-1 Leeb Rebound Hardness Testers

B-1.1. General Information

Leeb scale hardness testers are quite similar to the older Shore hardness testing method that consisted of a ball that was dropped through a glass tube and accelerated due to gravitational force onto the material surface to be tested. The Shore test represented the first attempt to measure hardness by observing the energy loss after the indenter rebounded from the test piece. In contrast, Leeb scale hardness testers use a spring force to accelerate the indenter into the pipe surface and represents a significant advancement of the dynamic hardness testing method(2,3). Rebound hardness testers based on the Leeb method have been available for about 30 years. Following expiration of Leeb’s original patents, the number of available Leeb scale rebound testers expanded considerably since their initial introduction. In 1995, a modified Leeb tester was introduced that contained multiple indenter velocity measuring coils that automatically compensated for gravity effects on the test. In 1997, the first edition of ASTM A956 was issued which provided standardized test criteria for this method. Additional Leeb hardness test standardization efforts by DIN in Europe are ongoing. Leeb scale rebound hardness testers are offered by several manufacturers and are available in different styles and configurations plus two different methods of compensating for the test position. All Leeb scale testers consist of a spring loaded impact device with a tungsten carbide (WC) ball (i.e., “D type”), an induction coil for indenter velocity measurements, a support ring, and an electronic display indicating the hardness plus other functions including hardness scale conversions. Some of these testers consist of one piece integral units with the body containing the impact device built into the electronic display while others have a separate impact body that is connected to the electronic package. In some cases, the impact body is offset to one side of the integral unit. Figures B-1 and B-2 are typical examples of the two types of Leeb hardness testers that are currently available.


B-2

Figure B-1. Integral Leeb Hardness Tester Figure B-2. Separate Indenter Type Leeb Tester(23, 24) The Leeb scale (L) hardness value is simply defined as the ratio of the indenter impact velocity (Vi) as it is accelerated toward the test piece and the rebound velocity (Vr) as follows(10,11).

i

r

VVL 1000=

The indenter impact creates localized plastic deformation of the test piece which causes the indenter to lose a part of its initial velocity and the rebound is driven by the elastic recovery. Lower hardness materials result in a greater velocity loss. Leeb rebound hardness testers can be used in all positions but the single coil indenter velocity measurement method, common to most available testers, is sensitive to the effects of gravity on the indenter during the test. As a result, such Leeb hardness testers require the application of a hardness correction factor when an indention is made in other than the vertical down position. In general, this correction factor is applied by programming the electronics package to automatically apply the required factor each time tests are conducted in other positions. If this capability is not included in the electronics package, the correction factors can be found in ASTM A956 for the different available indenter types. A different implementation of the Leeb tester produced by Krautkramer employs a dual coil indenter velocity measuring system that automatically applies the proper position correction factor(10,11,21). Different indenters are available for many of the Leeb testers shown in Table B-1(with different impact energies and tips) that are suitable for different materials and wall thicknesses. For steels used in pipelines, the most useful has been the “D” indenter with a 3 mm diameter tungsten carbide ball. Typically, the Leeb hardness (HL) scale result for pipeline steel materials with a “D” style indenter ranges from about 320-470. In itself, the Leeb hardness value is typically not used. Therefore, conversion to the more commonly used hardness scales such as Rockwell B (HRB), HRC, and others is typically part of test process.


B-3

B-1.2. Leeb Hardness Tester Thickness Considerations

As the indenter impacts the material surface, the impact energy (900 N or 202 lbf for a “D” indenter) creates surface plastic deformation and the rebound is driven by the elastic recovery. The impact energy imparted also creates a vibration in the test piece which can also further reduce the indenter rebound velocity. This vibration results in an artificial hardness reduction and also increases test scatter with decreasing pipe wall thickness. In addition to the wall thickness alone, the hardness reduction magnitude is also related to the pipe elastic ring stiffness as indicated by the diameter/thickness ratio or other measures(41). One example of the thickness effect on Leeb rebound hardness (“D” indenter) testing results and Vickers hardness testing (98 N) is shown in Figure B-3. It can be seen the Leeb (converted to Vickers hardness) and the standard Vickers hardness values are essentially equivalent above a wall thickness of about 0.79-inch (20 mm). For lower wall thicknesses, the actual Vickers hardness is greater than the converted Leeb hardness by the factor shown on the y-axis of Figure B-3(20).

Figure B-3. Comparison of Vickers and Leeb Hardness vs. Wall Thickness Another example of a similar relationship is illustrated by the results of pipe hardness tests conducted by the authors. Figure B-4 illustrates the difference between the hardness values made with a Leeb rebound hardness tester (converted to HRB) on pipe sections with different diameters and a range of wall thicknesses compared to direct HRB test data. The vertical axis indicates the HRB scale ratio of the lab and field test data. For the range of wall thicknesses shown, Figure B-4 indicates the HRB correction factor that should be multiplied by field test result to achieve equivalency with a standard HRB test result and should be included in any hardness-yield strength correlations. These data are very similar to that shown in Figure B-3.

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B-4

Figure B-4. Comparison of HRB and Leeb Hardness vs. Pipe Wall Thickness An evaluation of other similar data from the literature was also conducted. The relative elastic (compliance) ratio for two circular flat plates with the same diameter and different thicknesses under point loading at the center and supported at the rim is shown in Figure B-5. Again, this relationship is similar to Figures B-3 and B-4 except that the correction factor does not tend to begin rising rapidly until the wall thickness is less than shown in Figure B-3 and B-4. Compared to Figure B-4, this relationship indicates that the required Leeb hardness correction factor is a function of both the wall thickness (i.e., local mass) and the pipe stiffness(41).

Figure B-5. Calculated Pipe Stiffness Correction Factor for Leeb Hardness Testing(41) A similar graph reported in the same reference is shown in Figure B-6 except that it based on pipe compliance for pipe with different diameter/thickness ratios (D/t) that have been referenced to the compliance of a solid round bar. This relationship was derived from basic compliance expressions with some finite element analyses (FEA) validation up to a D/t ratio of 8.3. According to this reference, Figures B-5 and B-6 are used together depending on the pipe D/t ratio. For pipe with low D/t ratios, Figure B-6 provides the appropriate correction factor but the correction factor can never exceed that shown in Figure B-5 for the same wall thickness. Therefore, for larger diameter, high D/t pipe, Figure B-5 provides the appropriate correction factor according to Reference 41. It was also stated that the largest correction factor component is the pipe cross sectional dimensions(41).

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0.800.901.001.101.201.301.401.501.601.701.80

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Plate Thickness (in)

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Fact

or


B-5

Figure B-6. Calculated Pipe Stiffness Correction Factor for Leeb Hardness Testing Referenced To Solid Round Bar(41) When using a Leeb rebound hardness tester, the need for a hardness correction due to wall thickness can also be qualitatively evaluated by the audible sound of the impact. When a large, solid mass (such as the test block) is impacted, the audible sound can be described as a “click” which indicates surface vibrations are not a factor. However, when a thinner wall section is impacted by a Leeb indenter, the audible sound emitted is similar to a “bong” or like a bell ringing. This sound indicates that the recorded Leeb hardness will probably underestimate the actual material hardness and an appropriate correction factor should be applied to obtain the proper result. ASTM A956-02 states that the minimum test piece weight and thickness should be 15 lb and 0.125-inch respectively. Test pieces weighing less than 15 lb or with thicknesses less than 0.125-inch of any weight should be rigidly supported during a Leeb rebound test. However, considering the data from the literature and developed by the authors as shown in Figures B-3 through B-6, it does not appear possible to apply the ASTM stated limits to line pipe testing without applying a correction factor. Some specific considerations applied to Leeb rebound testers are:

• Tests by the authors indicate that for testing pipeline materials, a group of at least 10 tests should be used at each location. The HLD value standard deviation of each group of tests should be a maximum of about 10. If it is above 10, the test area should be re-prepared and re-tested. This requirement is similar to ASTM A956 repeatability criteria.

• It is recommended that the correction factor relationship with pipe wall thickness be used where Leeb testers are used on wall thicknesses less than about 0.875-inch.

• Each test area should be prepared by sanding in multiple steps through at least 180 grit abrasives. Excessively rough surface finishes can artificially lower the hardness value.

• Leeb testers are battery powered, portable, and suitable for testing in all positions with minimum clearance.

• Only small areas of coating must be removed and testing can be done without access to the full pipe circumference.

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orre

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B-6

• Ambient temperature extremes must be considered that typically range from about 32 to 120 F. The specific temperature range recommended by each manufacturer should be considered.

• The typical Leeb scale hardness test block furnished with a “D” type impact body has a HLD hardness of about 750. It would be desirable to have a test block more consistent with the material hardness range to be tested (i.e., HLD 320-470). Other Leeb scale test blocks are available such as with the “G” type impact body with a HLD of about 600 that exceeds the likely pipe test range. An alternative would be to attach a standard steel Rockwell B test block to surface of the standard Leeb test block (or a large, smooth steel section) with the coupling paste (furnished with Leeb testers) and calibrate directly using the HRB conversion contained in the Leeb hardness tester.

• When testing is conducted on individual pipe segments or coupons, the proximity of an open end will artificially lower the hardness value. It is recommended that hardness testing should not be attempted within 12 inches of an open pipe end.

• Due to the design of multiple coil Leeb tester impact bodies that compensate for position, the required indenter rebound travel distance is greater. Therefore, restrictions on the minimum hardness that can be accurately measured may exist since more rebound energy is lost during the impact. This should be evaluated prior to field test applications where lower hardness materials may be involved.

• The internal hardness scale conversion algorithms in all brands of Leeb rebound testers may not be equivalent to each and should be compared using a standard test block.

• Due to the impact body and support shoe design, precise placement of an indentation can be difficult to achieve. Therefore, if precise indentation locations are needed, an alternative hardness tester is recommended.

• It is extremely important that the Leeb tester impact body is firmly held on and is maintained perpendicular to the test piece surface during the test.

• The manufacturer or supplier of any Leeb scale hardness testers should state that their equipment is certified to be in compliance with the requirements of ASTM A956. Some available testers could contain design deficiencies that could lead to erroneous data.

• For Leeb testers with the impact body connected to the electronics package by a special cable, continued cable integrity under field conditions has been found to be problematic. It is recommended that at least one spare cable be immediately available during field testing.

B-2 Ultrasonic Contact Impedance (UCI)

This is an application of Vickers hardness testing except that the hardness is not determined from the hardness impression dimensions first used in 1967. A Vickers diamond indenter is attached to the end of a metal rod that is being resonated into a longitudinal oscillation mode at frequency of about 70 kHz by piezoelectric transducers. A typical UCI hardness tester is shown in Figure B-7(20,21). Such hardness testers are commercially available from several manufacturers.


B-7

Figure B-7. UCI Hardness Tester(21) When the load is applied to the rod by a spring, the indenter penetrates the test piece and the rod oscillation frequency changes in proportion to the indention contact area. This frequency shift will increase as the indentation area becomes larger in lower hardness materials. Since the frequency shift is proportional to the indention size and Young’s modulus, the hardness can be determined as described by the following equation where (C) is constant, (P) is the applied load, and (Af) is the measured frequency shift under load(20,21).

fAPCHV =

During the test, the UCI instrument monitors the oscillation frequency, performs the required calculations and displays the hardness level. Internal algorithms permit automatic conversions to other common hardness scales. In some cases, motorized probes are used for lower loads to minimize operator influence. UCI hardness testers have been used for field hardness testing on pipelines and components. Since the UCI analysis method is a function of Young’s modulus, a recalibration is required when testing materials with a different modulus value. UCI hardness testers have six available loads ranging from 0.1 N (0.1 kgf) to 98 N (10 kgf) depending on the application. For pipeline applications and particularly where conversions to material strength are anticipated, the 98 N load is required as stated in ASTM 1038-05(19). Since UCI testing may also create test piece flexural vibrations (similar to Leeb rebound testers) resulting from the indenter rod oscillations, hardness data scatter can become an increasing issue with thicknesses less than about 0.6-inch (15 mm). In any case, the test piece wall thickness should not be less than about 0.12-inch (~3 mm). A comparison between UCI data (HRB scale conversion) and laboratory HRB test data on pipe materials was conducted by a pipeline operator. Measurements were made over a wide range of pipe diameters (2 – 34 inch nominal OD) with wall thicknesses between 0.15 and 0.75 inch. Test surfaces were prepared using sanding discs with decreasing grit sizes down to 180. Figure B-8


B-8

illustrates the comparison of the laboratory direct HRB hardness data with the UCI data converted to HRB from unpublished test results conducted by the authors. The linear regression line shown (through the origin) indicates a reasonable correspondence between field and laboratory data with significant scatter in some cases. Although some significant scatter is evident, the overall correlation is reasonable.

Figure B-8. Comparison of Lab HRB to UCI Data Converted to HRB Additional comparisons between UCI data converted to HRB and direct HRB hardness measurements were made using the pipe wall thickness and diameter versus the difference between the field and laboratory test data as field HRB minus lab HRB. Figures B-9 and B-10 illustrate the hardness difference (field HRB minus lab HRB) or error plotted versus the pipe wall thickness and diameter respectively. With respect to pipe wall thickness, the most extreme scatter is evident when testing the thinner wall pipe which is consistent with the minimum wall thickness requirements discussed above. Similarly, Figure B-7 indicates more scatter when testing smaller pipe diameters. It should also be noted that data points located well below the regression line shown in Figure B-8 are primarily from 6-inch outside diameter (OD) and smaller pipe with half the data from 2-inch OD pipe. This suggests that smaller pipe diameters are more difficult to properly test in the field with a UCI tester and most likely related to the indenter probe not being held perpendicular to the pipe surface.

y = 0.9281x40.0

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B-9

Figure B-9. Effect of Wall Thickness on UCI Test Error

Figure B-10. Effect of Pipe Diameter on UCI Test Error From these data, some specific considerations for UCI hardness testers are:

• Small diameter pipe is more difficult to accurately test. This implies that the indenter alignment with the pipe surface is an important essential test variable.

• Lower pipe wall thicknesses increase hardness data scatter. • For thin wall pipe materials, loads less than 98 N would be preferable but this may

impact the accuracy of conversions to strength. • Surface preparation and finish requirements are more demanding to minimize test

scatter especially with lower loads. • Compared to Leeb rebound hardness testing, a UCI tester would be more appropriate for

field testing pipe with wall thicknesses less than 0.250-inch although increased scatter would be expected.

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• Data in the literature confirms the author’s experience that it is critical that test probe should remain firmly held and perpendicular to the pipe surface for the test duration.

B-3 Direct Reading Rockwell Hardness Testers

Several versions of a direct reading Rockwell scale hardness tester that can be used on pipe are currently available from Wilson-Instron specified as Models M-0 through M-9. Each of these testers has a range of available test loads from 15 to 150 kgf, allowing measurement in regular Rockwell (HRB, HRC) or Rockwell superficial scales. The testing force is applied by a pre-loaded spring mechanism. All of these hardness testers must be mounted on the pipe and utilize different mounting methods. The M-2 model shown in Figure B-12 has a C-Frame clamping system that would be suitable for small diameter pipe. Others are equipped with a chain or steel band wrapped around the pipe circumference with measurement head similar to that shown in Figure B-12. The M-8 model, shown in Figure B-11, is equipped with electromagnetic base and is reported to be applicable to 1.5 inch OD and larger pipe. No external power source is required for these portable testers except that 120V AC electrical power is required for the magnetic mount on the M-8 model(9). For pipeline testing, considering the yield strength estimation objective, it is recommended that HRB scale should be used to eliminate a required scale conversion. Therefore, the minimum wall thickness is 0.250-inch considering the test 100 kgf load required for HRB testing. Lighter loads using the Rockwell superficial hardness scales may permit their use on thinner wall pipe. Another reason for the 0.250-inch minimum wall thickness is to provide for an adequate magnetic coupling force for the M-8 model magnetic mount to prevent lift-off during the test. The magnetic mounted version, although considered portable, weighs about 42 lbs and could be difficult to transport and operate in difficult terrain. The chain mounted version (15-35 lbs) can be used in different positions while the magnetic mounted tester would be applicable primarily at or close to the top of a pipeline. Also, unless 120V AC power is locally available, an engine-generator would also be needed for the magnetic mounted tester. The portable models that are mounted with a chain or strap require access to the complete pipe circumference thus increasing the amount of excavation required at each test location. In order to properly attach such testers to a pipeline, the coating in the test area as well as completely around the pipe, in most cases, would require removal. Very little coating deformation could be allowed to maintain a tight mount that would resist lift-off as the test load is applied. Figures B-11 and B-12 illustrate the magnetic mounted and C-clamp tester models.


B-11

Figure B-11. Magnetic Mounted Direct Figure B-12. Clamp Type Direct Rockwell Tester(9) Rockwell Tester One of the major benefits in using these portable testers is that Rockwell B hardness values can be directly converted to published equivalent strength values without the need for intermediate conversions. Ultimately, this could benefit the accuracy of strength estimates from hardness test results since intermediate scale conversions are not required. Also, for Rockwell B testing (100 kg load, 1/16” diameter ball), surface preparation requirements are less stringent and reliable results with minimal scatter can be obtained without a high quality surface finish. A recent significant change in ASTM E 18 is that Rockwell B testing now must be conducted with 1/16-inch diameter tungsten carbide (WC) rather than steel ball indenters. Steel indenter balls may still be specified in product specification or hardness test procedure. Preliminary data indicates that WC balls tend to read about 1 HRB unit less than a steel ball. When HRB results are reported, it should be indicated which type of indenter ball was used. Some specific considerations applied to direct reading Rockwell testers are:

• The magnetic mounted version may not be useable where surface corrosion or roughness exists that could decrease the magnetic coupling force. Coating would need to be removed over about a length of 14 inches along the pipe axis to accommodate the mounting.

• The chain or band mounted version can be difficult to properly align and set up for testing especially where the pipe to be tested is not straight. Application to bends or elbows can be difficult. Complete access to the full pipe circumference is required for mounting.

• Testing cannot be done within restricted pipe access locations. For other than the top of the pipe, more clearance would be required as compared to other hardness testing methods.

• Except for the Model M-8 magnetic mounted tester, the others can reportedly be used in all positions. However, the author’s experience has indicated that testing in positions other than the top quadrant can be difficult to accomplish in practice.

B-4 Manual Indention Testers

Manual indentation hardness testers, sometimes described as “Rockwell like” hardness testers require the test technician to apply the test load. They consist of an electronics and data processing package that is coupled to the indenter device as shown in Figures B-13 and B-14.


B-12

Figure B-15 illustrates a test technician applying the test load. They are typically battery powered with some having a 120V AC power alternative. These testers use either conical diamond or ball indenters with hardness determined from calculations based on impression depth. Conversion to most common hardness scales is provided with internal algorithms. These testers are light and portable and may be used in any position assuming that sufficient space exists for the operator to properly apply the load(23,24).

Figure B-13. Manual Indentation Tester Unit(24) Figure B-14. Manual Indentation Indenter Body(24)

Figure B-15. Manual Indentation Load Application(23) As the test technician applies a load to the indenter device, a preload is first applied that is controlled by spring loading followed by the total test load. The maximum load magnitude is also controlled by the spring loading within the indenter device. As load is removed, the indention depth difference between the preload and maximum load is determined and the hardness value is calculated. Since the indenter device body rests directly on the test piece, any test piece deflection does not affect the hardness measurement. Therefore, this method is more suited to thinner materials than other hardness testing methods. One of these instruments uses a unique hardness scale described as “HRZ” which is then converted into the desired standard scale including HRB, HRC or others(24). Some specific considerations applied to manual indentation testers are:

• Load must be applied by the test technician while holding the tester squarely on the test surface. Therefore, access must be sufficient to accommodate the operator and test instrument. Although these hardness testers can be used in all positions, only the top and


B-13

sides of a pipeline could be realistically considered. In cases where the operator cannot evenly apply the test load, their usefulness would be limited.

• Testing can be done on thinner wall material without the need for correction factors as with the Leeb rebound testers.

• As with Leeb rebound and UCI hardness testers, only a minimal amount of coating must be removed.

• The role of the test technician is significant, requiring training to properly operate the test equipment.

B-5 Brinell Hardness Testing

The Brinell hardness test method relates metal hardness to the diameter of the test impression made by a ball indenter. For a given load, the hardness increases as the impression diameter decreases. Several types of portable Brinell testers are available that could be applied to pipeline field hardness testing. They include a clamp loading device and comparative testers that are typically impact loaded with a hammer down to a minimum of 1-inch OD. The clamp loading type would only be applicable to small diameter pipe (1-inch minimum OD) while the comparative “pin type” and “Telebrineler” are applicable on larger pipe diameters. The “pin type” incorporates a calibrated shear pin with a known shear load that is inserted into the indenter device against the indenter and driven into the test piece by a hammer impact or static load. The indenter is forced into the test material only as far as it takes for the shear pin to fail. The shear pins are calibrated which provides the basis for tester calibration. Excess applied load is absorbed by the indenter device body as the indenter moves into an internal cavity. The indentation diameter is then optically measured to determine the hardness. Figure B-16 shows a pin type Brinell tester (12, 23).

Figure B-16. Pin Brinell Tester(23) With pin Brinell testing, if the hammer blow does not break the shear pin, the load on the indenter will be less than the target load. Otherwise, if the hammer blow is sufficient to break the


B-14

shear pin, then the ball indenter applied load is sufficient. Shear pin failure prevents excessively high loads from being applied to the pipe surface. The Telebrinell tester is somewhat similar in that the indention force is provided by a hammer impact. For this method, the force is used to simultaneously drive two indenters; one into the test piece surface and the other into a calibrated reference bar that was selected to have a similar hardness level as the test piece. The indentation diameters in the reference bar and the test piece are then optically measured and compared with the ratio of the two indention diameters used to determine the pipe hardness value. Since the Telebrinell tester is based on a comparison of the hardness impressions on a known and unknown material, it is a self calibrating method. With Telebrinell testing, the applied pipe and test bar load is dependent upon the force of the hammer blow. Since the measured hardness value is affected by the applied load, the Telebrineller may be less accurate. However, the Telebrineller can produce usable results on relatively thin wall or large D/t pipe, whereas the same pipe may elastically deform sufficiently to prevent enough load from being applied to break the shear pin if using a pin Brinell test. In such a case, the load from the hammer blow causes the pipe to elastically deform before sufficient load is applied to break the shear pin. Any pipe on which the shear pin can be broken during the pin Brinell test without producing a dent on the pipe (other than the ball indenter impression) can be tested using the pin Brinell method. No hardness measurement is possible with the pin Brinell method if the pin does not break. However, a useable, hardness measurement can be obtained by the Telebrineller at loads that would be insufficient to break the shear pin in the pin Brinell method, although the pin Brinell test procedure specifies that the applied load should be sufficient to produce a dent of a specified size range in the calibrated test bar. Telebrinell tests that do not produce a large enough impression are invalid as a result of the applied load being outside the target range. Brinell hardness testing is typically performed with 10 mm diameter hardened steel or WC ball indenter with a maximum load of 3000 kgf load although 1500 kgf, 500 kgf, and lower loads can be applied. Smaller ball type indenters are also permitted by ASTM E10. The test piece minimum thickness should be such that no bulging or through wall deformation is evident on the opposite side of the pipe. Minimum thickness requirements for Brinnell testing are sometimes given as at least 10 times the impression depth but such guidelines typically apply to a supported test piece and not an unsupported pipe.

The remaining impression is comparatively large compared to other hardness testing methods and may not be suitable for all pipeline applications, especially in cases where ductility at the service temperature and fracture toughness may be marginal. Although, the pipe surface finish is not critical considering the indenter ball size and loading, it should be adequately prepared to facilitate an accurate indention diameter measurement. The ultimate accuracy of this method is largely dependent on the test technician’s ability and judgment. Therefore, sufficient training is an essential element in the success of field Brinell hardness testing.


B-15

Some specific considerations applied to portable Brinnell hardness testers are:

• Hammer impact type Brinell testing would be difficult to use in limited access areas or in all positions. It would be feasible only on the pipe sides provided sufficient excavation was performed and on the top of the pipe.

• One advantage of the method is that it samples a larger volume of the metal than either the ball rebound or UCI method. As such, it is less sensitive to large pipe grain size issues and the hardness reading is not affected by minimal surface preparation. However, the large remaining impression may not be suitable for all applications.

• Even through good surface preparation is not significant for creating a valid hardness indention, it does facilitate a more accurate indention diameter measurement.

• According to manufacturers, the minimum wall thickness for hammer impact testers that depend on a reference bar comparison is about 3/16-inch. However, if any test piece deflection results from the test, such a comparison would be invalid. The applicability of this method on pipe should be evaluated prior to testing.

B-6 TIV Vickers Method

A more relative and recently developed static field hardness testing method is “Transpyramidal Indenter Viewing” or “Through Indenter Viewing (TIV)” and is also known as the “Through Diamond Technique” (TDT). This is an application of standard Vickers hardness testing except that indention dimensions are measured under load. The TIV system consists of two components including the indenter body and Vickers diamond indenter and the computer/electronics package as shown in Figure B-17. The computer within the electronics package allows data accumulation and some statistical calculations(28, 29).

Figure B-17. Vickers TIV Hardness Tester(29) The indenter body shown in Figure B17 contains the loading mechanics and associated electronics, optics, and a CCD (charge-coupled device) digital camera that can create high resolution digital images under a variety of lighting conditions and allows the user to see through the indenter. The hardness is measured during the loading process and is immediately sent for


B-16

evaluation as the required test load is attained. At that point, the image of indenter is captured and an automatic hardness evaluation is made. Also, the operator can evaluate the indention and measurement quality plus observe the condition of the diamond indenter(28, 29). Two test loads are available including 5 kgf (50 N) and 1 kgf (10 N). Load is manually applied to the top of the indenter body by the operator (similar to the previously described manual indentation testers). This method is reportedly applicable to thin materials and mass does not affect the results. Internal conversion to other hardness scales including HRB per ASTM E140 is included. It can be powered by rechargeable batteries, standard c-cells, or a line current adapter(29). Some specific considerations applied to the TIV hardness testers are:

• The indenter body is comparatively large which would make precise location of indentions difficult and may also impact access.

• It is a self calibrating test method. • Preparation and pipe surface issues such as grain size would tend to affect this test

method similarly to the UCI method and more so than others like Leeb rebound and manual indentation testers.

B-7 Automated Ball Indentation (ABI) Method

Early work by Meyer and others covered in Section 3 of this Guide established that a true stress--true strain relationship could be determined from successively higher indentation loads in metals by a spherical indenter. This concept was advanced considerably within the past 20 years by development of the ABI method(13-16). ABI is an indentation depth sensing testing method that continuously records and processes indentation information and have been designed for both lab and field applications. The field applicable version typically consists of a laptop computer which controls the indentation system that is mounted on a pipe with straps or a magnetic shoe. Figures B-18 and B-19 show the two main components and an example of the portable version mounted on a pipeline(13).

Figure B-18. ABI System and Computer Control(13) Figure B-19. ABI System Mounted On Pipeline(13)


B-17

The computer continuously controls the load and displacement of an indenter as it is loaded and unloaded from the pipe surface. Based on the load-displacement data collected after several load/unload cycles, information such as a true stress–true strain curve can be generated thereby allowing yield and tensile strength estimates. Other information such as residual stress, basic hardness values, and fracture toughness (Kc) reportedly can also be estimated(14, 15, 16). ABI systems use different types of indenters including small diameter TC spherical (0.5 and 1.0 mm) and Vickers diamonds. Both battery and 120V AC power can be used in the field. Due to the size of the test head, additional coating removal would be required when compared to other field hardness testers such as the Leeb rebound or UCI. In cases where additional pipe material information is needed other than the basic conversion from hardness to strength, the ABI method is the only indentation test method capable of generating such data that is currently available(14-16). Some specific considerations applied to ABI hardness testers are:

• ABI systems can generate more data and can directly estimate yield and tensile strength without a need for conversion tables.

• Such testing would likely be performed by a qualified contractor rather than directly by a pipeline operator. Compared to typical field applicable hardness testers, ABI systems are expensive.

• Testing rates would be somewhat slower than typical field hardness testers. • Compared to smaller, more compact hardness testers, ABI system components and the

need for high quality 120V AC power may reduce field portability. Table B-1 summarizes some of the detailed operating parameters for numerous commercially available hardness testers that could be used for pipeline testing projects. In many cases, other manufacturers produce similar equipment that could also be used. It should be noted that Table B-1 applies to hardness tester availability at the time the data was compiled and is subject to change.


B-1

9

Tab

le B

-1 S

umm

ary

Cap

abili

ties o

f Sel

ecte

d H

ardn

ess T

este

rs

Mfg

M

odel

/No

. R

eqd

Pow

er

Scal

e In

dent

ion

Dev

ice

Ener

gy/L

oad

Des

ign

Acc

urac

y C

ompl

ianc

e C

ertif

icat

ion

Har

dnes

s M

easu

rem

ent

Pr

imar

y In

tern

al

Con

vers

ion

Type

D

escr

iptio

n D

irect

ion

.

Star

rett

3811

B

atte

ry

Leeb

Y

es

D

TC b

all

All

11 N

mm

(8 ft

-lbs)

In

tegr

ated

N

ot st

ated

N

o in

fo

Reb

ound

ve

loci

ty

Mut

itoyo

H

ardm

atic

H

H-4

01

Bat

tery

Le

eb

Yes

D

TC

bal

l A

ll

Sepa

rate

in

dent

er

±3%

A

STM

A

956

Reb

ound

ve

loci

ty

Proc

eq

Equo

tip 2

, 3

Bat

tery

Le

eb

Yes

D

TC

Bal

l

(3 m

m)

All

11 N

mm

(8 ft

-lbs)

Se

para

te

inde

nter

N

ot st

ated

N

o in

fo

Reb

ound

ve

loci

ty

Kra

utkr

amer

M

IC-2

0 (a

lso

UC

I)

Bat

tery

Le

eb

Yes

D

TC

Bal

l

(3 m

m)

All

Se

para

te

inde

nter

±3

%

AST

M

A95

6 R

ebou

nd

velo

city

Kra

utkr

amer

M

IC-2

0 (a

lso

Leeb

) B

atte

ry

Vic

kers

H

ardn

ess

Yes

V

icke

rs

Dia

mon

d A

ll 1-

10 k

gf

Sepa

rate

in

dent

er

~ 4%

of h

ardn

ess

Non

e kn

own

Dep

th se

nsin

g

Mic

roph

oto

nics

So

noha

rd

SH75

A

Bat

tery

or

AC

V

icke

rs

Har

dnes

s Y

es

Vic

kers

D

iam

ond

All

Se

para

te

inde

nter

±3

%

Non

e kn

own

Dep

th se

nsin

g

Wils

on –

In

stro

n M

-2

Non

e B

all,

Dia

mon

d N

o R

ockw

ell

Bal

l, D

iam

ond

All

15-1

00

kgf

Inte

grat

ed

Cal

ibra

tion

Blo

ck

Non

e kn

own

Dep

th se

nsin

g W

ilson

–

Inst

ron

M-6

N

one

Bal

l, D

iam

ond

No

Roc

kwel

l B

all,

Dia

mon

d A

ll 15

-100

kg

f In

tegr

ated

C

alib

ratio

n B

lock

N

one

know

n D

epth

sens

ing

Wils

on –

In

stro

n M

-7

Non

e B

all,

Dia

mon

d N

o R

ockw

ell

Bal

l, D

iam

ond

All

15-1

00

kgf

Inte

grat

ed

Cal

ibra

tion

Blo

ck

Non

e kn

own

Dep

th se

nsin

g W

ilson

–

Inst

ron

M-8

12

0 V

AC

B

all,

Dia

mon

d N

o R

ockw

ell

Bal

l, D

iam

ond

Top

15-1

00

kgf

Inte

grat

ed

Cal

ibra

tion

Blo

ck

Non

e kn

own

Dep

th se

nsin

g Pr

oceq

Eq

uost

at

Bat

tery

H

RZ

Yes

D

iam

ond

80ºC

one

All

50 N

Se

para

te

inde

nter

±

2 H

RC

N

one

know

n D

epth

sens

ing

Erns

t C

ompu

tes

t B

atte

ry o

r A

C

Dep

th C

alcu

l Y

es

Dia

mon

d C

one

All

49 N

Se

para

te

inde

nter

±

1HR

C

Non

e kn

own

Dep

th se

nsin

g

Erns

t D

ynat

est

Bat

tery

or

AC

D

epth

Cal

cul

Yes

D

iam

ond,

TC

bal

l C

one

All

980

N

Sepa

rate

in

dent

er

± 1H

RC

N

one

know

n D

epth

sens

ing

Erns

t Es

ates

t B

atte

ry o

r A

C

Dep

th C

alcu

l Y

es

Dia

mon

d C

one

All

9.8

– 98

N

Var

iabl

e Se

para

te

inde

nter

U

nkno

wn

Non

e kn

own

Dep

th se

nsin

g

Kra

utkr

amer

V

icke

rs

TIV

B

atte

ry,

120

VA

C

Vic

kers

Y

es

Vic

kers

D

iam

ond

All

10 N

, 50

N

Sepa

rate

In

dent

er

Not

stat

ed

Non

e kn

own

Aut

omat

ed o

ptic

al

inde

ntio

n si

ze

mea

sure

men

t

Fron

tics

AIS

300

0 B

atte

ry,

120

VA

C

WC

Bal

l or

Dia

mon

d Y

es

TC B

all,

Dia

mon

d

0.5/

1.0

mm

dia

m.

or V

icke

rs

Top

300

kgf

max

. In

tegr

al

Dep

ends

on

type

of

mea

sure

men

t

AST

M S

td

bein

g de

velo

ped

Dep

th se

nsin

g

New

age

Pin

B

rinel

l N

one

Brin

ell

No

10 m

m B

all

TC o

r st

eel

Top,

side

H

amm

er

impa

ct

NA

C

alib

rate

d Sh

ear p

in

± 1

unit

Non

e K

now

n O

ptic

al d

iam

eter

m

easu

rem

ent

Tele

wel

d Te

leB

rine

ll N

one

Brin

ell

No

10 m

m B

all

TC o

r st

eel

Top,

side

V

aria

ble

ham

mer

im

pact

N

A

± 3%

of t

est b

ar

Non

e kn

own

Com

para

tive

diam

eter

m

easu

rem

ent


C-1

APPENDIX C Selected Industry Codes/Standards

This Appendix lists selected domestic and foreign codes and standards that are relevant to the hardness testing process. This includes those relating directly to hardness testing as well as other aspects of the process including surface preparation. C-1. Hardness Testing Standards

1. ASTM E140-05, “Standard Hardness Conversion for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Superficial Hardness, Knoop Hardness, and Scleroscope Hardness.”

2. ASTM E384-06, “Standard Test Method for Microindentation Hardness of Materials.” 3. ASTM E103-84 (Reapproved 2002), “Standard Test Method for Rapid Indentation

Hardness Testing of Metallic Materials.” 4. ASTM E110-82 (Reapproved 2002), “Standard Test Method for Indentation Hardness of

Metallic Materials by Portable Hardness Testers.” 5. ASTM E10-07, “Standard Test Method for Brinell Hardness of Metallic Materials.” 6. ASTM E18-07, “Standard Test Methods for Rockwell Hardness and Rockwell

Superficial Hardness of Metallic Materials.” 7. ASTM A1038-05, “Standard Practice for Portable Hardness Testing by the Ultrasonic

Contact Impedance Method.” 8. ASTM E92-82 (Reapproved 2003), “Standard Test Method for Vickers Hardness of

Metallic Materials.” 9. ASTM A956-02, “Standard Test Method for Leeb Hardness Testing of Steel Products.” 10. ASTM A833 - 84 (Reapproved 2001), “Standard Practice for Indentation Hardness of

Metallic Materials by Comparison Testers”. 11. ASTM A370-07, “Standard Test Methods and Definitions for Mechanical Testing of

Steel Products.” 12. ISO 6507-1:2005, “Metallic Materials—Vickers hardness test—Part 1, Method”. 13. ISO 6507-2:2005, “Metallic Materials—Vickers hardness test—Part 2, Verification and

calibration of testing machines”. 14. ISO 6507-3:2005, “Metallic Materials—Vickers hardness test—Part 3, Calibration of

reference blocks”. 15. ISO 6507-4:2005, “Metallic Materials—Vickers hardness test—Part 4, Hardness values”. 16. ISO 6508-1:2005, “Metallic Materials—Rockwell hardness test—Part 1, Method (scales

A,B,C,D,E,F,G,H,K,N,T)”. 17. ISO 6508-2:2005, “Metallic Materials—Rockwell hardness test—Part 2, Verification and

calibration of testing machines (scales D, E, F, G, H, K, N, T)”. 18. ISO 6508-3:2005, “Metallic Materials—Rockwell hardness test—Part 3, Calibration of

reference blocks (scales A, B, C, D, N, T)”. 19. ISO 14577-1:2002, “Metallic Materials—Instrumented indentation test hardness and

materials parameters-- Part 1, Testing”. 20. ISO 14577-2:2002, “Metallic Materials—Instrumented indentation test hardness and

materials parameters-- Part 2, Verification and calibration of testing machines”. 21. ISO 14577-3:2002, “Metallic Materials—Instrumented indentation test hardness and

materials parameters-- Part 3, Calibration of reference blocks”.


C-2

22. ISO 18265:2003, “Conversion of hardness values”. C-2. Surface Preparation

1. ASTM E3-01, “Standard Guide for Preparation of Metallographic Specimens.” 2. ASTM Manual E-46, “Metallographic and Materialographic Specimen Preparation, Light

Microscopy, Image Analysis and Hardness Testing”, 2007.


D-1

APPENDIX D Hardness Test Locations Within a Pipe Length

This Appendix establishes the rationale for selecting hardness testing locations within each pipe length sampled. A review of relevant data pertaining to pipe strength and hardness variations was conducted to establish a method of establishing sampling locations to obtain the most realistic strength estimate of each pipe included in the test sample. For primary heat tensile testing of welded pipe according to API 5L, the test location within a pipe length is specified at a position relative to the longitudinal seam but the location along the pipe length is not. However, test coupons are typically removed from a pipe end. Similarly, 49 CFR Part 192, Appendix B requirements for conducting tensile tests to establish the strength of unknown pipe references API 5L test criteria with no other provisions other than the number of pipe lengths that must be subjected to testing. It is left to the user to establish criteria for the test location along the pipe length. It is well known that pipe tensile properties can vary within a single pipe length, in pipe produced from a heat of steel, and over a pipe lot comprised of multiple heats. Most of this variation results from the plate or skelp properties and not the pipe manufacturing process. Considering the wide pipe manufacturing time span that is the focus of this Guide (earlier than 1980), it is anticipated that a variety of steel making processes will be represented when conducting field hardness testing of pipe. Also, due to the various steel manufacturing processes, the pipe tensile property variation would not be consistent. Therefore, for pipe hardness testing purposes, it is considered prudent to specify test locations within a pipe length that would account for such variation. Pipe produced from steel manufactured in 1980 and earlier represents a considerable part of the steel manufacturing process evolution. Pipe manufactured during this time period could be made from steel produced by both ingot and continuous casting methods. Earlier steels were semi-killed with higher impurity levels that gave way to fully killed steels with lower impurity levels that were achieved though control methods such as desulfurization and vacuum degassing. Properties of earlier steels were primarily achieved through their chemical compositions. In the 1960’s, microalloyed steels began to appear in line pipe production. The properties of the latter steels were developed from a combination of lean chemical compositions and more complex plate/skelp rolling schedules. In addition to the influence of different steel manufacturing methods, pipe tensile property variation is a result of the plate/skelp rolling practices. Property variation is also a function of the steel manufacturer’s capabilities and experience. Factors such as steel composition variations, initial heating temperature, starting slab uniformity, rolling reduction schedules and rolling temperatures all affect the tensile strength and its variation(D-2). Steel intended for line pipe production has been hot rolled on more conventional9 reversing plate/strip mills and Steckel10 mills that result in different property variation patterns. DSAW

9 Conventional skelp rolling mills have upcoilers located at both ends of the rolling line.


D-2

pipe has been produced from plate produced as single units, from multiple plate units that are then cut to size, and plates cut from coiled skelp. End-to-end variation within a coil also impacts ERW pipe. Within a single plate or coil, the ultimate distribution of tensile properties can also depend on the end orientation during hot rolling with respect to its alignment in the pipe mill. That is, the front end of the coil during hot strip production becomes the back end on the pipe mill. Similarly, plate tensile property variation can be a function of the front and back positions during rolling and may be reversed during pipe manufacturing. Seamless pipe can also be similarly affected but the manufacturing process is considerably different. An evaluation of data was conducted to determine the tensile property variations found in pipe and coiled skelp to optimize field hardness testing locations. This included field hardness testing data that considered pipe produced in the 1960’s and data contained in a 1999 report that addressed pipe produced in the 1990’s using more recent steel making and pipe rolling technology(D-1,D-2). Hardness testing results conducted by the authors included pipe in a natural gas pipeline facility constructed in the 1960’s. Leeb rebound hardness testing was conducted on ~ 70 individual pipe segments that included both DSAW and seamless pipe with varied lengths. Depending on the pipe length, as many as six locations on each were subjected to testing including both ends and the middle. Other pipe lengths were tested only at both ends. The maximum hardness variations within each pipe length were considered as well as the location variation of the high and low values. Figure D-1 illustrates the end-to-end hardness variation within a single pipe segment by plotting the high value/low value ratio versus the cumulative probability. The highest ratio for seamless and DSAW were 1.12 and 1.14 respectively which are significant and should be considered when developing a hardness test procedure. However, as illustrated by the cumulative probability shown as the y-axis of Figure D-1, the most likely end-to-end variation will be lower With respect to end-to-end test location differences, the highest DSAW pipe hardness value occurred near the middle of the pipe 60% of the time and at a pipe end 40% of the time. The location of the end-to-end high value in the seamless pipe was equally divided between the middle and ends but the sample size was small. These data suggest that no clear trend exists between a pipe end or middle sampling location, which indicates a single sample location at either an end or near the middle of the length would be appropriate(D-1). Figure D-2 is a graph similar to Figure D-1 except that it summarizes the side-to-side variation found in the pipe that was hardness tested. It can be seen that the maximum difference is about the same as the end-to-end variation.

10 A Steckel mill is a reversing hot strip rolling mill that utilizes hot upcoilers located on both sides of the rolling stand. The thermal cycling is different from more conventional plate/strip rolling mills and the resulting tensile property variation within a coil is not the same.


D-3

Figure D-1. End-to-End Hardness Variation

Figure D-2. Side-to-Side Hardness Variation The second source of tensile property variations included information and data from multiple sources that were compiled and analyzed. This report considered the variations in plate and coils of steel that was manufactured in the 1990’s. As such, these data represent more recent steel making practice using lean chemical compositions, microalloyed, and controlled rolling practices that included thermo-mechanical controlled processing (TMCP) and on-line accelerated cooling (OLAC) in some cases. However, controlled rolled steels have been used for line pipe manufacturing since the early 1960’s so the trends illustrated are relevant. Two of the data sets included yield and ultimate tensile strength data from steel plate rolled for line pipe production. The first data set consisting of six plates showed that the highest yield strength occurred at the front (head end) of four plates and the low was either in the middle or at the back end of the other two plates. This confirms that the plate orientation in the rolling mill makes a difference for plate produced using more advanced rolling practices. The second data set illustrating yield strength variation in three plates showed that the highest values occurred at the back end of each plate with the low value at the middle position of two and the front on one.

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.00 1.05 1.10 1.15

High/Low Hardness Value Within Pipe Length

Cum

ulat

ive

Prob

abilit

y

DSAW

SMLS

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.00 1.05 1.10 1.15

High/Low Hardness - Side-to side

Cum

ulat

ive

Prob

abilit

y

DSAW

SMLS


D-4

These two data sets indicate that the highest yield strength would most likely occur at one end of a pipe length with the lowest value at the middle of the pipe length or at the opposite end(D-2). Other data from a large plate that was rolled and then cut into two or more segments for pipe production was also considered in Reference D-2. Figure D-3 is a graph showing the yield strength differences over the plate length along both edges and the center. It can be seen that depending on where the plate is cut, the yield strength distribution along the length would vary.

Figure D-3. Plate Yield Strength Variation A similar situation exists with coiled skelp that is cut into individual plates for DSAW pipe production or continuously welded during ERW pipe production. In some cases, the yield strength tends to be lower at the coil ends or very little difference was found over the coil length. Yet another variation has occurred in coil produced on Steckel rolling mill where the yield strength of the pipe manufactured from steel near the center of the coil was significantly lower than the intended pipe SMYS. This was a result of the differences in thermal history between skelp produced as a conventional hot strip and a Steckel rolling mill. Considering the skelp and plate tensile property variations described above, it would be prudent to focus on the lower yield locations of pipe lengths selected for hardness to obtain a conservative yield strength estimate. The data suggests that for older pipe produced on conventional hot rolling mills, no significant systematic variation was evident. Therefore, a single randomly selected location in a pipe length would be appropriate. However, for steel more recently produced by controlled rolling practices (~1960 and later), the data indicate the highest yield strengths tend to be at the pipe ends. Therefore, it is recommended that initial pipe lengths selected for hardness testing include the middle of the pipe and one end. If no systematic variation is found, then the remaining pipe should be tested at one location. Field chemical analysis could be used to determine if typical microalloying elements are present (i.e., Nb, V) that could aid in determining if it was likely that the steel making included controlled rolling methods.

69.0

70.0

71.0

72.0

73.0

74.0

75.0

76.0

77.0

0.0 20.0 40.0 60.0 80.0

Distance From Front End (ft)

Yiel

d St

reng

th (k

si)

Plate Edge

Middle

Plate Edge


D-5

REFERENCES D-1. Clark, E. B., Unpublished hardness test data, 1992. D-2. Gray, J. M., et.al., “Tensile Property Variation in DSAW and ERW Line Pipe,” Report to

PRCI, Microalloying International, 1999. D-3. Clark, E. B., Unpublished ERW pipe production data.


E-1

APPENDIX E Hardness Test Procedure Qualification Record

(PQR)

Scope: This qualification record applies to hardness test procedures written in accordance with the criteria in the

Guide. General Date:________ PQR Number: ___________ Test Technician Name: ________________________ Hardness Tester Type:____________ Mfg:__________ Serial or ID Number: ________ Indenter Type:

Steel Ball: WC Ball Diameter (in):______

Diamond: Type:_______ Indenter Serial Number: ________

Test Pipe Diameter (in): ________ Wall Thickness (in): ________ Seam Type: __________ Calibration Block: Hardness Scale:_______ Hardness/Tolerance:________

Serial Number:_______

Ambient Temperature (F): ___________

Qualification Range

Pipe Diameter(in): ≥ 10 ≤ 8 ( ≤ 8 inch test pipe qualifies for all diameters) Minimum Wall Thickness(in):_________ (No less than the measured test pipe wall thickness) Pipe Circumferential Clock Position:________

Tester Load:________ Units:________ Optional Indenter Alignment Support: Yes No


E-2

Surface Preparation Sequence (Performed by Test Technician)

Preparation Grinder Sanding Disc Flapper Wheel Step Grit Size

1 2 3 4 5

Grinding is only permitted for Step 1

Pre and Post Procedure Qualification Hardness Tester Calibration Results

Test Number Prequalification Post Qualification Hardness Scale:_________

1 2 3 4 5 6 7 8 9

10 Average (a)

Std Deviation (b) COV (b/a)

Note: This requirement applies to both the field and lab hardness testers.

Qualification Pipe Field Hardness Test Results (Performed by Test Technician)

Test Number Pipe Clock Position Hardness Scale:____________ Loc. 1:________ Loc. 2:_________ Loc. 3:_________

1 2 3 4 5 6 7 8 9

10 Average (a)



E-3

Qualification Pipe Lab Hardness Test Results


1 2 3 4 5 6 7 8 9

10 Average (a)


Field/ Lab Test Result Comparison

Average Hardness Results Qualification Original Corrected Original Corrected Field-Lab Pipe Location Field Test Field Test(1) Lab Test Lab Test(2) Difference

1 2 3

(1) May require wall thickness and/or diameter correction factor. It is assumed that Leeb

rebound test indenter position corrections have been included. (2) May require diameter correction factor

Note: The field test average hardness must be within + 2% and – 4% of the lab average value (See Section 9) Procedure Qualification Results Acceptable: Yes No Remarks:_____________________________________________________________________________________ _____________________________________________________________________________________ Test Technician:___________________________________ Approved:________________________________________


F-1

APPENDIX F Hardness Test Technician Qualification Record

(TQR)

Scope: This qualification record applies to test technician qualifications in accordance with hardness test

procedures that comply with this Guide. General Date:________ Reference Hardness Test Procedure Identification: ___________ Test Technician Name: ________________________ Hardness Tester Type:____________ Mfg:__________ Serial or ID Number: ________ Indenter Type:

Steel Ball: WC Ball Diameter (in):______

Diamond: Type:_______ Indenter Serial Number: ________

Test Pipe Diameter (in): ________ Wall Thickness (in): ________ Seam Type: __________ Calibration Block: Hardness Scale:_______ Hardness/Tolerance:________

Serial Number:_______

Ambient Temperature (F): ___________

Qualification Range

Pipe Diameter(in): ≥ 10 ≤ 8 ( ≤ 8 inch test pipe qualifies for all diameters) Minimum Wall Thickness(in):_________ (No less than the measured test pipe wall thickness) Pipe Circumferential Clock Position:________

Tester Load:________ Units:________ Optional Indenter Alignment Support: Yes No


F-2

Surface Preparation Sequence (Performed by test technician being qualified)(a)

Preparation Grinder(b) Sanding Disc Flapper Wheel Step Grit Size

1 2 3 4 5

(a) Location must be immediately adjacent to preparation by a qualified test technician

to permit a direct comparison of test results. (b) Grinding is only permitted for Step 1.

Pre and Post Test Technician Qualification -- Hardness Tester Calibration Results

Test Number Prequalification Post Qualification Hardness Scale:_________

1 2 3 4 5 6 7 8 9

10 Average (a)


Test Technician -- Pipe Field Hardness Test Results (Performed by test technician being qualified)


1 2 3 4 5 6 7 8 9

10 Average (a)



F-3

Qualified Test Technician -- Pipe Field Hardness Test Results (Performed by qualified test technician)


1 2 3 4 5 6 7 8 9

10 Average (a)


Pipe Field Hardness -- Test Result Comparison

Average Hardness Results Technician Being Qualified Qualified Technician

Qualification Actual Corrected Actual Corrected Pipe Location Results Results (1) Results Results (2) Difference

1 2 3

(1) May require wall thickness and/or diameter correction factor. It is assumed that Leeb rebound test indenter

position corrections have been included. (2) May require diameter correction factor

Note: The difference in average pipe test hardness levels between the test technician being qualified and the qualified test technician must be within + 2% and – 4%. Test Technician Calibration Block Test Results (Performed by test technician being qualified)

Test Number Calibration Block Clock Position Hardness Scale:____________ Loc. 1:________ Loc. 2:_________ Loc. 3:_________

1 2 3 4 5 6 7 8 9

10


F-4

Test Number Calibration Block Clock Position Average (a)


Note: The average hardness at each test position must be within the calibration block tolerance. Test Technician Qualification Results Acceptable: Yes No Remarks:____________________________________________________________________________ ____________________________________________________________________________________ Test Technician:___________________________________ Valid Technician Qualification Period:___________________ Approved:________________________________________


G-1

APPENDIX G Statistical Methods Background

Section 10 of this Guide provides an overview of the methods used for determining the minimum required sample size for each homogeneous pipe lot and a lower bound hardness estimate from the data obtained. This Appendix provides additional background material and derivation of the statistical methods adopted. G-1. Background

The following nomenclature is used in this Appendix and Section 10:

minx A statistic that that is used as a minimum hardness value. Since the hardness values are considered to be normally distributed, this is not a true minimum; rather it is a cutoff for rare events. Specifically, it is rarely expected for values below minx to occur by chance.

*α Probability of seeing values smaller than minx . Thus, *α constitutes the definition of rare for this application. It can be defined to be any positive value, but 0.001 or 0.01 are recommended signifying that values smaller than minx on average would be expected once in every 1000 or 100 times respectively by chance.

*αz Standard normal distribution cutoff value with the area under the normal

distribution to the left of the cutoff being *α .

minx̂ Estimate of minx based on sampled data.

µ Population mean of the hardness distribution.

x Hardness distribution estimated mean of the based on sampled data.

σ Standard deviation of the population hardness distribution.

S Estimate of the hardness distribution standard deviation based on sampled data.

N Pipe sample size.

α Significance level of the confidence interval about µ and σ. Specifically, a one sided 100× (1-α ) % confidence interval is used. A recommended α value is 0.05 corresponding to a 95% confidence interval.

)1,( −Nt α The α cutoff value from a Student’s t-distribution with N-1 degrees of freedom.


G-2

21 ,1 −− Nαχ The α cutoff value for a Chi-square distribution with N-1 degrees of

freedom. The sample size calculation adopted assumes that the yield strength distribution and therefore the hardness variation of each homogeneous section of pipeline can be reasonably represented by a normal statistical distribution. In addition to the normal distribution, two other statistical distributions namely the Student’s t and Chi-square have also been incorporated into the sample size calculations as indicated in the above nomenclature. Normal distributions are characterized by two parameters; namely, the mean (µ) and the standard deviation (σ). If these were known for the section of pipeline under consideration, then the minimum hardness level could be taken to be a value that should rarely occur under this normal distribution. For this application, this hardness level is taken to be one below which would occur by chance once in a specified number of samples; typically one in every thousand or one in every hundred samples depending on the desired results. This is described as the area under normal distribution at or below a specified “cutoff” value. Figure G-1 shows a standard normal distribution with the cutoff value being the right boundary of the gray region shown. This value can be easily determined for (µ=0, σ =1) by using standard normal tables. Cutoff values from such tables usually are denoted by *αz where randomly drawn

observations are expected to be below *αz by chance [(1- *α ) × 100]% of the time. The symbol *α is used instead ofα to prevent confusion with another use of α later. The normal cutoff

*αz can be transformed to a non-standard normal distribution of hardness measurements, which is denoted as minx , by the Equation G-1: σμ α ×−= *min zx (G-1)

where the distribution of yield strength measurements has a mean of µ, standard deviation of σ.

Figure G-1. Normal probability density distribution with a cutoff at -2 While there is no theoretical minimum value for a tail of a normal distribution, a cutoff level can be chosen such that the probability of an observation being smaller than that cutoff is a rare

-4 -2 0 2 4

0.0

0.1

0.2

0.3

0.4

x

y


G-3

occurrence. In the case depicted in Figure G-1 with a cutoff of -2, it would be expected that an observation would be less than -2 about .023 percent of the time. That is, between 2 and 3 in 100 observations would be expected to be below -2. As an example, suppose the population mean HRB hardness level (µ) = 61 and the standard deviation (σ) was = 4.0. From the standard normal tables, the cutoff value for the left tail probability of *α =1/1000 is z0.001 = -3.090. Using Equation G-4 gives a minimum hardness level estimate of minx = 61.0 - 3.090 × 4.0 or minx = 48.63. By contrast, if a minimum hardness level that would occur once in every 100 samples were desired (instead of 1 in 1000 samples), a cutoff of z0.01= -2.326 would be used. In this case, the minimum yield strength estimate would be minx = 61 - 2.326 × 4.0 or = 51.69. Thus, a 1/1000 chance (a comparatively more precise requirement) gives are lower minimum than a 1/100 chance for the minimum yield estimate. In the preceding example, it was assumed that the mean and standard deviation of the pipeline population hardness levels were known. In practice this is not the case and these parameters must be estimated from a sample of the population data. Such statistical parameter estimates introduce uncertainty that needs to be accounted for when determining the required sample size. The more samples taken, the lower the uncertainty will be as associated with the hardness test results. In the following paragraphs, background and equations are provided that give insight as to how this methodology was developed for this application. As defined in the nomenclature, the symbol “ x ” is used to indicate the sample mean and the symbol “S” is used to indicate the sample standard deviation. Thus x is an estimate for µ and S is an estimate for σ. Standard computations of the sample mean and the sample variance for the number of samples (N) are given by Equations G-5 and G-6.

N

xx

N

ii∑

== 1 (G-2)

( )

11

2

−

−=∑

=

N

xxS

N

ii

(G-3)

As larger samples are collected, the estimates for the population mean and standard deviation become more precise, while for smaller samples the uncertainty in these estimates can be large. The notion of “large” can be quantified with the standard formulas for confidence intervals about the mean and standard deviation respectively. For this application, the primary interest is in the minimum hardness level that could occur so the one-sided lower confidence interval as depicted in Figure 1 is appropriate.

Figure G-2 shows examples of estimating a standard normal distribution using Equations G-2 and G-3 with the sample size (N) of 2, 5, 10, 50, 100, and 1000. In each case this was repeated five times. This would be analogous to five different people randomly sampling N samples from


G-4

a length of pipeline. As seen in the first figure, when N = 2 the distributions picked by different samples are highly variable. Minimum estimates like the one shown in Figure G-2 would be very different among the five people sampling. As N gets larger, the distributions become more stable and the minimum estimate is more stable. Thus an estimate of the minimum hardness value needs to account for the variability in the distribution due to the sample size. This variability is accounted for by using confidence bounds for µ and σ.

N=2 N=5

N=10 N=50

N=100 N=1000 Figure G-2. Fitted Normal Distributions from N Samples Taken from a Standard Normal Distribution when N is 2, 5, 10, 50, 100, and 1000 (Going Left to Right, Top to Bottom)

-4 -2 0 2 4

0.0

0.5

1.0

1.5

-4 -2 0 2 4

0.0

0.2

0.4

0.6

0.8

1.0

-4 -2 0 2 4

0.0

0.1

0.2

0.3

0.4

-4 -2 0 2 4

0.0

0.1

0.2

0.3

0.4

-4 -2 0 2 4

0.0

0.1

0.2

0.3

0.4

0.5

0.6

-4 -2 0 2 4

0.0

0.1

0.2

0.3

0.4


G-5

Equations G-4 and G-5 give the one-sided confidence intervals for the normal distribution parameters µ and σ. A strictly proper interpretation is that if the data were re-sampled and confidence intervals were also determined for each sample, a specified number of these confidence intervals (e.g., 95%, 99%) would contain the true population parameter, but here the confidence interval is less strictly interpreted as the probability of the true parameter lying in the confidence interval. Equations G-4 and G-5 make use of the Students t- and Chi-square distributions. A primary parameter of both of these distributions is the “degrees of freedom” which is defined as the sample size minus 1 or N-1.

μα <−−NSNtx )1,( (G-4)

21 ,1

2)1(−−

−<N

SNαχ

σ (G-5)

where N is the sample size, )1,( −Nt α is the cutoff value from a t-distribution with N-1 degrees of freedom and 2

1 ,1 −− Nαχ is the cutoff from a Chi-squared distribution also with N-1 degrees of freedom. Here, [(1-α ) ×100]% is the confidence level on the lower tail confidence bound associated with respective distribution. It is also noted that value of α considered in Equations G-4 and G-5 need not be the same as *α used with the normal distribution. This is why *α was used earlier. A typical value of α would be 0.05 implying a 95% confidence interval. However, if *α were set at a value of 0.05, this would mean 5 in every one hundred observations would be expected to be lower which is not the best choice for a minimum hardness test result estimate. Therefore, a *α value of 0.001 representing 1 in every 1000 pipe lengths selected for hardness testing from a homogeneous population would be expected to have a lower hardness value by chance. Equations G-4 and G-5 are utilized by considering these bounds as reasonable worst case estimates and using them as worst case parameter estimates for the normal distribution of hardness levels. Thus, the lower bound estimate for the mean of the population mean ( μ ) and the upper bound estimate for the population standard deviation (σ ) will be used for sample size estimates. Combining Equation G-1 with Equations G-4 and G-5 yields:

21 ,1

2

min)1()1,( *

−−

−−−−>N

SNzNSNtxx

αα χ

α . (G-6)

The sample standard deviation (S) in the last two terms can be factored out giving:


G-6

⎟⎟⎠

⎞⎜⎜⎝

⎛ −+−×−=−−

21 ,1

min)1(1)1,(ˆ *

N

NzN

NtSxxα

α χα (G-7)

Here the term minx̂ instead of minx since it is estimated based on sample data and the inequalities have been removed. Equation G-7 can then be used in two ways. The factor in parentheses is independent of the observed data and can be used before hardness data collection to determine sample size. After hardness data are collected, Equation G-7 can be used to estimate the expected minimum value within the pipe population being sampled. G-2 Sample Size Determinations

In the preceding section, Equation G-7 was developed giving an estimate for the minimum hardness level. In Equation G-7, α is associated with the parameter estimates from hardness data collected. Typically α = 0.05, and *α is the confidence level associated with the minimum estimate. Values of *α = 0.001 or 0.01 are recommended since they imply that only 1 in every 1000 or 100 pipe lengths sampled would be expected by chance to have a hardness level lower than minx̂ . Since the terms contained within the parentheses in Equation G-7 are independent of sample data and depend on the sample size, they can be pre-calculated. Using these pre-calculated values (termed Subtraction Factors), Equation G-7 has been reduced to a simpler form as Equation G-8. ( ) FactorSubtrationSxx ×−=minˆ . (G-8) Subtraction Factor values for α = 0.1, 0.05, and 0.01 for a range of sample sizes (N) have been calculated and shown in Table G-1. Section 10 includes sample calculations.


G-7

Table G-1. Equation 8 Subtraction Factor for α = 0.1, 0.05, and 0.01 with α* = 0.001, 0.01, and 0.05

α = 0.05 α = 0.01 α = 0.05 α = 0.01 α = 0.05 α = 0.012 59.670 269.041 46.092 208.403 33.854 153.7493 15.329 34.688 11.974 27.107 8.949 20.2744 10.199 18.064 7.980 14.180 5.980 10.6795 8.284 13.014 6.481 10.225 4.856 7.7126 7.278 10.654 5.691 8.372 4.259 6.3147 6.653 9.293 5.197 7.300 3.885 5.5038 6.223 8.404 4.857 6.598 3.626 4.9709 5.907 7.777 4.607 6.101 3.435 4.591

10 5.663 7.307 4.413 5.730 3.286 4.30711 5.469 6.943 4.258 5.440 3.167 4.08612 5.310 6.649 4.131 5.207 3.069 3.90713 5.177 6.408 4.025 5.015 2.987 3.75914 5.063 6.206 3.934 4.854 2.917 3.63515 4.965 6.033 3.856 4.716 2.856 3.52916 4.880 5.884 3.787 4.597 2.803 3.43717 4.804 5.753 3.727 4.492 2.755 3.35618 4.737 5.638 3.672 4.400 2.713 3.28419 4.676 5.535 3.624 4.318 2.675 3.22120 4.621 5.443 3.580 4.244 2.641 3.16321 4.572 5.360 3.540 4.177 2.610 3.11122 4.526 5.284 3.503 4.116 2.581 3.06423 4.484 5.215 3.469 4.061 2.555 3.02124 4.446 5.151 3.438 4.010 2.530 2.98125 4.410 5.093 3.410 3.963 2.508 2.94426 4.377 5.039 3.383 3.919 2.487 2.91027 4.346 4.988 3.358 3.879 2.467 2.87928 4.317 4.941 3.334 3.841 2.449 2.84929 4.290 4.898 3.312 3.806 2.432 2.82230 4.264 4.857 3.292 3.773 2.415 2.796

N α* = 0.001 α* = 0.01 α* = 0.05Subtraction Factor

The data shown in Table G-1 for α = 0.05 and 0.01 (95% and 99% confidence bounds) with α* = 0.001 are plotted in Figure G-3. Notice the significant subtraction factor increase as the sample size decreases. This illustrates the effect of less sample data on the width of the confidence bounds. Conversely, the marginal subtraction factor decrease attributed to larger samples sizes is also shown in Figure G-3. This occurs since the curve shown is a function of one over the square root of the sample size (N) (with some other lesser effect N dependencies).

0

5

10

15

20

25

30

35

0 2 4 6 8 10 12 14 16 18 20

Subtraction Factor

Sam

ple

Size

(N)

Alpha=0.05 Alpha=0.01

Figure G-3. Subtraction Factor vs. Sample Size [α = 0.05 and 0.01(95% and 99%confidence bounds), α* = 0.001] Equation G-8 and Table G-3 can be used either to estimate sample size or to compute the estimate of the minimum yield strength.


H-1

APPENDIX H Field Hardness Testing Data Sheet

A. LOCATION

B. PIPE DESCRIPTION B1. Pipe OD (in) B2. Pipe Coating

Type B3. Pipe Seam Type

B4. Nominal/ Actual Wall Thickness (in)

B5. Corrosion (External/Internal)

/ Yes No

Seamless Lap / Hammer BW/CW SAW/DSAW ERW Other Arc welded Flash Not Visible, unknown

B6. Pipe Temp. (F) B7. Pulsation or Vibration

B8. Evidence of rehab B9. Long Seam Clock Position

Yes No Yes No

C. TEST SET UP AND CALIBRATION C1a. Hardness Tester Type C2a Indenter Type C3a. Calibration Block

Hardness/Tolerance

C1b. Tester Serial # C2b.Indenter Serial # C3b Calibration Block Serial #

C1c.Indenter Support Method Manual Fixture

C4. Preset Calibration Selected from Memory

Yes, # __________ No

C5. Calibration Data Test Results

Test Number Pre-Test Mid- Test Post Test 1 2 3 4 5 6 7 8 9

10 Time

Average Std. Dev.

A1. Pipeline Number A2. Stationing A3. Other Location Descriptor


H-2

D. PIPE SURFACE PREPARATION (Report for each pipe length tested)

D2. Sanding grits

D5. Longitudinal Pipe Position (from girth

weld, ft)

D6. Circumferential Pipe Position

(clock)

D7. Proximity of test location to seam, welds, arc burns,

mechanical damage: Prep. Step

1 2 3 4 5 D3. Measured thickness before prep (in) D4. Measured thickness after final prep (in)

E. TEST DATA (Reproduce as necessary) Pipe Length Number or Identification

1 2 3 4 5 6 7 HRB Hardness Applicable Guide

Equation 1 2 3 4 5 6 7 8 9

10 Average= Section 10, Equation 9 Std. Dev.= Section 10, Equation 10

Standard Error

of Average Section 13, Equation 11

Test Uncertainty

(U) Section 13, Equation 12

Longitudinal Pipe Position

Circumferential Pipe Position

F. TEST DATA CORRECTIONS

Correction Factors

Pipe Column Average HRB Hardness From Table E

Test Uncertainty (U) From Table E

Average Minus U

Indenter Probe Angle

Pipe Thickness

Pipe Curvature

1 2 3 4 5 6 7

Avg


H-3

G. CONVERSION TO YIELD STRENGTH (Reference 1, Table A.3.8)

Proportion (Targeted Percentile)

Confidence Level (%)

Equivalent Yield Strength (psi)

Inspector:____________________________Date _________ Reviewed By: _____________________ Date __________

Inspector Qualifications Verified?

Yes No


I-1

APPENDIX I Effect of Pipe Pressure on Rebound Hardness Tester Results

Information suggesting that pipe pressure changes would alter the results of Leeb rebound hardness testers has been circulating for some time although the authors have not seen any documentation that would support this allegation. Presumably, the increased stiffness of a pressurized pipe system would be increased with pressure and therefore alter the rebound characteristics thus changing the hardness value measured. In order to verify the veracity of this information, two tests were conducted that consisted of Leeb hardness testing on pipe that was being slowly pressurized with water. The diameter/thickness (D/t) ratios were 34 and 88. The pipe surfaces were prepared by sanding consistent with the requirements of this Guide. Figure I-1 shows the results of the first test on a pipe section with D/t ratio of 34. The first tests were taken prior to filling the pipe section with water and then at zero pressure after filling. It can be seen that the addition of the water increased the Leeb hardness value. This suggests that the water added mass and was effectively coupled to the pipe which increased the Leeb hardness as shown in Figure I-1. Thereafter, tests at 100 psig pressure increments up to 875 psig alternated above and below the average hardness with no apparent trend.

Figure I-1. Variation of Leeb Hardness with Pressure (D/t=34) A second test was conducted on a pipe section being pressurized with water with a D/t of 88. This testing started at zero pressure on the water filled pipe and was tested at 100 psig increments up to 1000 psig. Figure I-2 summarizes the results of this test. These results are same as observed from the first test; the hardness values also alternated above and below the average hardness with no apparent trend with increasing pressure. These test results indicated that pressure did not affect Leeb hardness data and testing of a pressurized pipeline would not affect the results. The hardness variation observed was primarily a result of the local differences in the pipe steel.

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405

Empty Water, 0

100 200 300 400 500 600 700 800 875

Pressure (psig)

Leeb

Har

dnes

s (L

d)

Average Hardness


I-2

Figure I-2. Variation of Leeb Hardness with Pressure (D/t=88)

REFERENCES I-1 Clark, E. B., Unpublished data.

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Pressure (psi)

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J-1

APPENDIX J Surface Roughness Considerations

Hardness tester, related references, and manufacturer’s documentation often quote surface preparation information for particular hardness testers and indenter types. Surface roughness parameters are important with respect to optimizing the results of hardness testing. Unfortunately, such requirements are frequently stated in different scales and units. The purpose of this Appendix is to provide information concerning these requirements and equivalencies(J-1 – J-

4). The following table provides a relationship between the surface finish resulting from different sandpaper grit sizes. This applies to either aluminum oxide or silicon carbide abrasives on soft steel. Table J-1. Abrasive Grit Size Equivalent Surface Finish

Abrasive Grit Size Surface Finish (microinches, Ra)

80 80

150 35 220 25 280 20 320 16 400 7 600 2

In Table J-1, the surface finish is listed in terms of a “Ra” value11. This defines the arithmetic mean of the absolute values (in the given units) of the profile differences within a measured surface length. Other surface finish related conversions are as follows: Microinch(µin)/40 = Micrometer(µm) (J-1) Table J-2. Surface Roughness Conversions

Surface Roughness Parameter Factor

Rt 8.7 Rz 7.2

Rz (ISO) 7.6 Rmax 8.0

Rp 3.6 RPM 2.9 RMS 1.1

From Table J-2, conversions are made by: Ra x Parameter = Equivalent Parameter (J-2)

11 Somewhat different Ra values are found in the literature and depend on the source- foreign or domestic.


J-2

For reliable hardness test results, the final surface finish must not leave a profile that approaches the dimensions (depth and area) of the indentation. If the surface is too rough, the result will most likely be artificially low hardness data since the indentation only penetrates the surface profile and not the actual steel surface. An example of the variation in Vickers hardness with several surface conditions is provided in Figure 14 of Reference 20. This provides an indication of the reduction of test variation associated with surface condition up to a 320 grit finish. In this case, no comparison was made to a polished surface.

REFERENCES J-1 Anon, “Stone Code Explanation Chart & Surface Finish Guide.” J-2 Anon, “Key Facts For Pharmaceutical Process Engineering,” Bovis Lend Lease. J-3 Anon, “Sandpaper (coated abrasives),” www.sizes.com/tools/sandpaper.htm. J-4 Anon, “Ra surface conversion chart,” www.finishing.com.


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