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High Strength Microalloyed Linepipe: Half a Century of Evolution 23

Chemical Composition

WeightPercent

C Mn Nb (Cb)Min. 0.20 0.89 0.004

Max. 0.27 1.28 0.015Mean 0.24 1.10 0.008

Table 1: Chemical Composition of semi-killed niobium steel [1].

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In retrospect the carbon content was still relatively high since carbon contents have steadilydecreased, Figure 3, as strengths have increased and larger amounts of microalloyingelements have become necessary. The current limit on the combined microalloying content Nb+V+Ti for steels with yield strength >60 ksi is 0.15 percent [18-19]. Individual limits are presented in Figure 4.

Figure 3: Relationship between carbon content and yield strength for high strength pipelinesteels [16].

Figure 4: Comparison of limits for vanadium and niobium for different pipe grades.

There has been a steady increase in available yield strengths from 52 ksi in the 1950’s to 120ksi today Figure 5.

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Figure 5: Line pipe grade evolution

Despite the considerable amount of research on X-100 and X-120 steels since 1985 and 1998respectively [20-32] pipes with strengths above 80 ksi have yet to see commercial service in pipelines, even though they have been incorporated into the latest revisions of Internationalspecifications [18-19]. Small quantities of X-100 linepipe have been installed in the TransCanada System [33] to demonstrate construction feasibility, but the pipe nevertheless isoperating at a relatively low stress (0.60 SMYS) relative to its real capability.

The metallurgy of X-90 to X-120 linepipe is based on very low carbon microalloyed steels,additionally alloyed with molybdenums, chromium, nickel, copper and occasionally boron,Table 2, combined with elegant TMCP cooling practices, Figures 6 & 7. Some of theseconcepts have been adopted in second generation X-70 and X-80 steels.

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Figure 6: Four processing methods utilized in TMCP, conventional ACC, intensified ACC,and intensified ACC with low FCT or normal coiling, and their characteristics in control of

microstructures with reference to a CCT diagram. Figure 7: Relation between Pcm value andtensile strength for various cooling methods.

Figure 7: Relation between Pcm value and tensile strength for various cooling methods.

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High Strength Microalloyed Linepipe: Half a Century of Evolution 27

During evolution of linepipe steels over the period depicted in Figure 5, several essentialevents, chronicled below, can be credited with changing of specifications or with stimulatingmetallurgical developments in both linepipe and plate steel.

These factors are presented in Table 3 below:

Date Event Industry Reaction

1943 Discovery of ductile-brittle transition incarbon steels.

Introduction of 15 ft-lb CVNenergy requirement intospecifications for ship plate.

1954 Above characteristics considered relevant to pipelines.

TÜV introduced 3.5mkg/cm2 energyrequirement for pipelines.

1960 Brittle fracture propagation of 13 km in NPS30 pipeline.

Development of Battelledrop weight tear test(BDWTT).

Dec. 1968 -Jan. 1969

Propagating ductile fracture in non-brittle,supposedly crack resistant, material.

Introduction of minimumCharpy energy requirements based on various fracturemodels.

1970 Proposed construction of Alaskan/ Canadiangas pipelines (CAGSL)

Steel development frenzycentered on X-80 (551 MPa)and -69°C (-90°F) toughnessrequirements.

1972HIC failure in X-65 BP pipeline in Ummshaif(Arabian) Gulf.

Introduction of BP test(NACE TM-02-84 [SolutionB]).

1974 Unpredictable fracture arrest in full scale(CAGSL) tests. Attributed to rich gas,separations, high hoop stress and faultymodels.

Introduction of crackarrestors, improved fracturearrest modeling and revisionof rolling ideas for highstrength linepipe.

1978 Stress corrosion cracking failures in newlyinstalled Australian and Canadian pipelines.

Better metallurgical(hardness) controls andimproved external coatings.Improved operating practices.

1978 Molybdenum "shortage" and price escalation. Mo designed out of X-70steels. Nb-Cr designintroduced plus TMCP.

1988/89 Vanadium price increase to $50/kilo Vanadium eliminated frommany steels. Mo and Cr +TMCP substituted.

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small (5 km) demonstration projects. The workhorse grades for onshore pipelines arecurrently API Grade X-70 (482 MPa) and API Grade X-80 (550 MPa) with the latter takingon increasing importance.

The chemical compositions in current use are presented in Table 6 below. Niobium andvanadium may be used in combination with molybdenum, chromium, copper and nickeldepending on pipe wall thickness, alloy costs and available manufacturing equipment. Each pipe mill thus arrives at an optimized steel composition and production cost matched to it’sengineering capability.

Type C Mn Nb V Ti Mo Cr Other* Nb-V 0.08 1.63 0.04 0.08 0.013 0.10 - Cu, Ni

Nb-Mo 0.04 1.68 0.08 - 0.015 0.30 - 0.30 Cu 0.20 Ni Nb-Cr 0.03 1.70 0.095 - 0.013 0.10 0.28 Ni

* S<0.005 N<0.008 Al 0.02-0.05

Table 6: Examples of X-80 Steels in Current Use.

The Nb-Cr alloy design has emerged in the past few years as a favorite of Chinese [34-44]and other pipe producers. The 0.10 percent niobium (HTP) steel has a much wider processing window than conventional Nb-V type steels, Figures 9-11 [45] which results inless variation in toughness and yield strength, the later being an important consideration in thecurrent regulatory climate in the United States.

Figure 9: Wide Processing Window for Yield Strength of 22 mm Plates ACC at 6ºC/s [45].

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High Strength Microalloyed Linepipe: Half a Century of Evolution 31

Figure 10: Wide Processing Window for Tensile Strength of 22 mm Plates ACC at 6ºC/s [45].

Figure 11: Wide Processing Window for Charpy Toughness of 22 mm Plates ACC at 6ºC/s[45].

Figure 12: Tensile Strength of 3,200 HTP Plates, ArcelorMittal Burns Harbor Plant, USA[45].

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Industry specification have been updated in many countries to accommodate the HTP concept[1819] and over 5 million tons of this very low carbon steel have been installed since 1972[48]. However, there are still opportunities for changing restrictive microalloying elementlimits in specifications in Iran, India, CIS and elsewhere.

Figure 13: Progress in adopting X-80 Steel [33].

The rate of adoption of API Grade X-80 since 1985 is presented in Figure 13 above. A listof the projects comprising Figure 13 is presented in Table 7 [47]. The growth is becomingexponential as API Grade X-80 is being utilized in China for major portions of the 9250 kmSecond West-East Pipeline Project [33].

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High Strength Microalloyed Linepipe: Half a Century of Evolution 33

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The steels used for production of large diameter DSAW linepipe are processed onconventional plate mills [30, 47, 48], Steckel mill facilities [49], or heavy strip mills (for 24inch diameter spiral seam linepipe), whereas skelp for HFERW linepipe is produced either onconventional hot strip mills or increasingly by direct conversion of thin (50-125 mm) slabs.

Typical steel compositions for Grade X-80 linepipe produced on a conventional hot strip millare presented in Table 8 [45-46].

Table 8: Chemical compositions of API Grade X-80 ERW linepipe.

Seamless product for use in linepipe and oil and gas riser systems is becoming available instrengths up to the 90-100 ksi level and is invariably produced by quenching and tempering.In recent years carbon contents have been reduced to below 0.10 percent to improve fieldweldability, to improve weld heat affected zone (HAZ) toughness and fatigue resistance, andto reduce HAZ hardness so as to improve SSC resistance.

Examples of the chemical compositions of seamless linepipe are presented Table 9 below[52-54]:

Grade C Mn Si Ni Nb V Cu Mo Cr B Dia. wt. Ref.

X-80 0.04 1.50 0.15 1.00 0.06 - 0.90 0.25 0.50 - 8" 19.1mm [52]

X-80 0.06 1.29 0.20 0.019 - -0.03

-0.0008

14" 25.4mm

[53]

X-70(sour)

0.07 1.35 0.15 - 0.03 0.05 - 0.16 - - 10" 34.0mm

[54]

Table 9:Chemical composition of API Grade X-80 Seamless linepipe.

The aforementioned examples of linepipe steel compositions mainly relate to product required

for low temperature or sweet (i.e. treated non-corrosive) gas service. However, manydevelopments have occurred in regions producing gas containing H2S, CO2 and chlorides.Depending on the concentrations of each of the above, the moisture content and ease andfeasibility of inhibition, the end user may elect to use either carbon steels or more highlyalloyed corrosion resistant grades. Examples of modern sour service carbon steels used for production of DSAW linepipe for the Black Sea Pipeline are presented in Table 10 below[56].

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High Strength Microalloyed Linepipe: Half a Century of Evolution 35

Table 10: Chemical Composition of 30” O.D. X -65 31.8 mm Linepipe (Blue Stream Project)[55].

Steelmaking and Manufacturing Developments

At their inception microalloyed (HSLA) steels were based on Open Hearth or Basic ElectricArc steelmaking. Thus there were limitations on reducing carbon contents (to improvesolubility of niobium and titanium) and impurity levels were very high. Typical sulfur and phosphorus levels were around 0.025 percent and sometimes twice this level. This level ofsulfur had a very detrimental on notch toughness especially when combined with the very

high oxide contents of semi-killed steel.

Sequential technical demands for improved linepipe referenced earlier in Table 3 eventuallyled to dramatic improvements in steel cleanness, reduction in impurities such as phosphorusand sulfur, as well as reduced nitrogen and hydrogen contents. These developmentsoccurred very rapidly inthe 1970’s and 1980’s especially in Japan [56 -58] Figure 14 andwere similarly adopted in Europe. The benefit of reduced sulfur on Charpy shelf energy is presented in Figure 15.

Figure 14: Progress in improving impurity removal through 1985.

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Figure 15: Effect of sulfur content on toughness of linepipe.

Other manufacturing developments occurring since 1959/60 in response to end user demands, production economics, new test methods (e.g. HIC testing) and other factors discussed inthis and other* papers are presented chronologically in Table 11 below:

Year Item1960’s Greater usage of fully-killed steel.1960 Normalizing of linepipe plate.1967 Controlled rolling adopted.1968 Continuous casting applied.1971 Pig iron desulfurization developed.1972 Inclusion shape control industrialized.1972 Calcium argon blowing introduced.1974 Slag free tapping practices. (Phos. reduction).1975 Nitrogen or argon stirring.1977 Degassing adopted on large scale.1978 Plate stacking for hydrogen control.1978 TMCP and direct quenching.1978 Top and bottom blowing.1979 Steel desulfurization.1983 Soft reduction.1986 Interpass cooling of austenite.1992 Thin slab casters used for linepipe.

Table 11: Manufacturing Developments 1960-2009

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High Strength Microalloyed Linepipe: Half a Century of Evolution 37

Examples of the chemical compositions of X-65 sour service linepipe produced with the newtechnology (circa 1995) are presented in Table 12.

Table 12: Chemical Composition of API Grade X-65 for Sour Service

Evolution of Linepipe Producers & Production

As stated earlier manufacturing technologies for all HSLA steels improved rapidly from 1970onward often due to demands from the linepipe arena. The demands occurred regionally,

first in Alaska and later in the North Sea, followed by the demand for massive volumes of 56”OD X-70 (K60) linepipe from the former Soviet Union from 1970 through 1992 at which point the market collapsed.

Middle East demands from Saudi Arabia, Oman, Iran etc were for sour service X-60 andX-65 grades. In North America Canadian gas transmission companies such as TCPL andWest Coast Energy led the move to higher strength levels.

For example: X-70 Nb-Mo steel was adopted by TCPL in 1970 produced at that time byIPSCO from semi-killed ingot steel [59]. Nowadays the pipe is produced from fully-killed

continuously cast very low carbon (0.035%) skelp [60].In the 1990’s there was diversified demand on pipe makers in traditional steelmaking regionsfrom projects offshore China and Brazil, from the Gulf of Mexico and the Middle East.Starting in 1999 Indian and Chinese pipe producers emerged mostly equipped with modernsteelmaking and pipe making facilities. India became a major exporter of line pipe to NorthAmerica, whereas Chinese demand was generated internally. Between 1999 and 2005Chinese producers developed API Grade X-70 and utilized it for the First West East PipelineProject [33] which extends 4500 km from the autonomous regions of Lunnan andHao’er’guosi in the West to Shanghai in the East. After 2 005 API X-80 was systematicallydeveloped and in a crowning achievement is being used for approximately half of the SecondWest East Pipeline Project (18.4 to 25.0 mm x 48” OD). A list of major large diameter pipemills in China with details of their estimated production capacities and size ranges is presented in Table 13. A listing of Indian pipe mills is shown in Table 14.

Globalization of Procurement

In the early 1970’s pipe manufacturer were located close to traditional steelmaking factoriesin Germany, UK, USA, Canada and Japan and Italy. Later, pipe making became moreInternationalized and increasingly non-integrated see Table 15 below and 16 for longitudinalseam and helical respectively. For example countries such as Turkey, Greece and India have built pipe manufacturing facilities based on imported coils or plate, meanwhile procurement

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Table 15: Compilation of Large OD Longitudinal Seam Pipe Mills Worldwide

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[10] “Strong Tough Structural Steel”. Scarborough, U.K., April 4 -6, 1967. ISI SpecialPublication No. 104

[11] J. L. Cuddy, “The Effect of Microalloy Concentration on the Recrystallisation ofAustenite During Hot Deformation” Proc. Thermomechanical Processing ofMicroalloyed Austenite Pittsburgh, PA August 17-19, 1981, AIME, TMS pp129-140.

[12] Isao Kozasu et al., “Hot Rolling as a High -Temperature Thermo-Mechanical Process”,Microalloying ’75 Conference Proce edings; October 1-3, 1975, Washington, DC, pp.120-135.

[13] F. B. Pickering and T. Gladman. “An Investigation into Some Factors whichControl the Strength of Carbon Steels”. Metallurgical Developments in CarbonSteels. Harrogate, U.K., ISI Special Report 81, May 1963

[14] R. B. G. Yeo, A. G. Melville, P. E. Repas and J. M. Gray. “Properties and Controlof Hot-Rolled Steel”. Journal of Metals Vol. 20, pp. 33 -43, 1968

[15] P. A. Peters & J. M. Gray, "Genesis and Development of Specifications andPerformance Requirements for Modern Linepipe - Strength, Toughness, CorrosionResistance and Weldability", Australian Pipeline Industry Association, Inc. 1992International Convention; Hobart-Tasmania, Australia; October 24-29, 1992.

[16] J. M. Gray and Peter A. Peters, "Technical Demands and Specifications for LinepipeDuring the Past Decades". CBMM/TSNIICHERMET Seminar - 25 Years ofCooperation. Moscow Russia. September 5-6, 2002

[17] C. L. Altenburger, “Columbium (Niobium) Treated, Low Carbon Semi -Killed Steel”,AISI Regional Technical Meeting No. 59, Buffalo, N.Y., 1960

[18] J. Hammond, “Development of Standards & Specifications for High StrengthLinepipe”, Paper Presented at International Symposium “Microalloyed Steels for theOil & Gas Industry”, Araxa MG, Brasil, January 23-26, 2006. Published by TMS

[19] John Hammond and J. Malcolm Gray, “Development of International Standards forLinepipe”, Rio Pipeline 2007, October 02 -04, Rio de Janeiro, Brasil

[20] A. Glover, “Application of Grade 550 and 690 in Arctic Climates”, Proc. ofApplication & Evaluation of High Grade Linepipe in Hostile Environments Conf., Nov. 2002, Yokohama

[21] L. Barsanti, R. Bruschi, and E. Donati, “From X80 to X100: Know -how reached byENI Group of High Strength Steel” Proc. of A pplication & Evaluation of High Grade

Linepipe in Hostile Environments Conf., Nov 2002, Yokohama[22] Fairchild et al. “High strength steels - beyond X80” Proc. of Application & Evaluation

of High Grade Linepipe in Hostile Environments Conf., Nov 2002, Yokohama[23] C. W. Petersen, K. T. Corbett, D. P. Fairchild, S. D. Papka, M. L. Macia, “Improving

Long Distance Gas Transmission Economics-X120 Development Overview”, Proc

4th Int’l Pipeline Technology Conf, Oostend, Belgium, May 9 -13, 2004

[24] S. D. Papk a, J. H. Stevens, M. L. Macia, D. P. Fairchild, C. W. Petersen, “Full -SizeTesting and Analysis of X120 Linepipe” Oil & Gas J., Vol. 102.8

[25] H. Asahi, T. Hara, E. Tsuru, Y. Terada, M. Sugiyama, N. Maruyama, H. Morimoto, K.Shinada, K. Koyama, M. Murata, N. Doi, H. Miyazaki, T. Yoshida, N. Ayukawa, H.

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High Strength Microalloyed Linepipe: Half a Century of Evolution 43

Akasaki, 2004, “Metallurgical Design of High Strength Steels and Development ofX120 UOE Linepipe”, Proc 4th Int’l Pipeline Technology Conf, Oostend, Belgium,May 9-13, 2004

[26] N. Nozaki, T. Hashimoto, Y. Komizo, H. Nakate and J. M. Gray "A NewLow-Carbon-Niobium Steel Designed for Accelerated Cooling" Proc. AcceleratedCooling of Steel Pittsburgh, PA, August 19-21, 1985 TMS/AIME pp 331.

[27] L. E. Collins. “X -100 Linepipe; A Canadian Steelmaker’s Perspective”, Materials forResource Recovery & Transport. Proceedings of the International Symposium - TheMetallurgical Society of CIM. Calgary, Alberta, August 16-19, 1998, pp. 251-266

[28] Moriyasu Nagae, Shigeru Endo, Noritsugu Mifune, Noriaki Uchitomi and OsamuHirano. “Development of X -100 UOE Line Pipe”. NKK Technical Review No. 66,1992

[29] Tamotsu Hashimoto, Yu-ichi Komizo, Masatoshi Tsukamoto, Yishihiko Shirakawaand Akira Yamashita. “Recent Development of Large Diameter Line Pipe (X -80

and X-100Grade)”. The Sumitomo Search, No. 37, November 1988[30] Dr. Hans-Georg Hillenbrand, Dr. Andreas Liessem, Dr. Gerhard Knauf, Dr. Jurt

Niederoff and Dr. Jurgen Bauer. “Development of Large -Diameter Pipe in GradeX-100”, Pipeline Technology, Vol. 1, p. 469 , Brugge, Belgium, May 21-24, 2000

[31] R. K. Ohm, J. T. Martin and K. M. Orzessek. “Characterization of Ultra HighStrength Linepipe”, Pipeline Technology, Vol. 1, p. 483, Brugge, Belgium, May21-24, 2000

[32] A. Glover et al, “The Application of X -100 to Gas Pipeline” Symposium“Microalloyed Steels for the Oil & Gas Industry”, Araxa MG, Brasil, January 23 -26,2006. Published by TMS

[33] Yi-Kang Wang, Jia-Hua Pan, Ke Yang and YiYin Shan “High PerformanceMicroalloyed Line Pipe Steel China”, Proceedings of Microalloyed Steels for the Oiland Gas Industry Symposium, TMS, 2007, pp. 135-179.

[34] Wang Xiao Xiang “The Development of Grade X -80 Linepipe and Induction Bendsin China” TRGC Seminar on X -80 Linepipe Steels, Xian PRC June 2008.

[35] Zhu Lixia et al “Effect of M/A Constituents on Mechanical Properties of X -80Linepipe Steels” Proceeding “International Seminar on X -80 and Higher Grade LinePipe Steel 2008”, Organized by CNPC -TGRC Xian, PRC June 23-24, 2008, pp.156-158.

[36] Kong Junhua et al “Exp erience of Mass Produced X-80 Strip for the Second WestEast Gas Pipeline”, ibid pp. 231 -234.

[37] Zhang Yongqing et al “Chemical Design Microstructure and Properties of Hot -RolledStrip”, ibid pp. 235.242.

[38] Huong Yixin et al “Production Practice of X-80/X100 Pipeline Steels by SteckelMill”, ibid pp. 243 -247.

[39] Sun Weihua et al “Development and Production of X -80 Pipeline Steel Plates” ibid pp. 254-258.

[40] Ma Quiurong et al “Research and Evaluation of X -80 SSAW Linepipe”, ibid pp.259-262.

[41] Li Weiwei et al “Study on Toughness of X -80 Pipeline Steel Welding HAZ”, ibid pp

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129-132.[42] Liu Wencheng “Demand and Development of X -80 Pipeline Steel for the Second

West-East Pipeline Project”, ibid pp 13 -18.[43] Nie Wenjin “Control of Fracture Toughness at Low Temperature for X80 Steel Plates

with Heavy Thickness”, ibid pp 104 -111[44] Wang Shuren et al “Analysis and Study of the Strength of Grade X80 Coil”, ibid pp

172-177.[45] M. Lin and R. L. Bodnar, “Effects of Comparsion and Processing Conditions on a

0.03%C-0.095% Nb X-70 Linepipe Steel”, 40th MWSP Conference Proc. ISS 1998

pp. 575-589.[46] J. Malcolm Gray and A. B. Rothwell, “Application Experience with X -80 Linepipe”,

CNPC International Pipeline Steel Forum, Beijing PRC, March 19-20, 2008[47] J. Schröder, V. Schwinn, A. Liessem “Recent Development in Sour Service

Linepipe” Proc. International Symposium on Microalloyed Steels for the Oil & GasIndustry Araxa, MG, Brasil, January 23-26, 2006. Published by TMS.

[48] O. Reepmeyer, W. Schuetz, A. Liessen and F. Grimpe “Very Heavy Wall X -70DSAW Pipe for Tension Leg Applications” ibid pp 109 -122.

[49] L.E. Collins, D.L. Baragar, J.T. Bowker, M.M. Kostic, S.V. Subramanian. “SteckelMill Process Optimization for Production of X-70 and X-80 Gas TransmissionLinepipe”. Microalloying ’95 Conference Proceedings; Pittsburgh, Pennsylvania;June 11-14, 1995, pp 141-147.

[50] A. Belloni, H. Kashimura et al, “Manufacturing and Welding on an X -80 (HFERW)Pipe - A New Technical Approach”, Pipelin e Technology Conference, Vol. II,

Oostend, Belgium; September 11-14, 1995, pp. 161-172[51] J. G. Williams, C. R. Killmore, F. J. Barbaro, A. Meta and L. Fletcher. “Modern

Technology for ERW Linepipe Steel Production (X-60 to X-80 and Beyond)”,Microalloying ’95 Conference Proceedings; June 11 -14, 1995; Pittsburgh,Pennsylvania; June 11-14, 1995, pp. 117-139

[52] B. M. Kapadia, Y. Adonyi, J. D. Defilippe and W. F. Domis, “Development of HSLA

Steel with 80 ksi Yield Strength for Offshore Tubular Applications”, Proc 11th

OMAE International Conference, 1992, pp. 73-79[53] A. Asahi, H. Fujii and N. Sato, “Heavy Wall X -80 Seamless Linepipe”, Pipeline

Technology Conference, Oostend, Belgium; Vol. II, pp. 253-262[54] Dalmine Siderca Tamsa (DST) private communication[55] J. Malcolm Gray, “Niobium Bearing Steels in Pipeline Projects” Proc. International

Symposium, Niobium 2001, Orlando, Florida, USA, December 2-5, 2001. Published by TMS p

[56] K. Yamada and T. Usui, “The Role of Hot Metal Pretreatment and the Converter process for Clean Steel Production” Proceeding of Conference Inclusions andResiduals in Steel, Ottawa, Ontario March 4-5, 1985 p3

[57] M. Sasabe, Testsu-to-Hagane 69:1831;1983[58] I. Kozasu and K. Tsukada, “The Metallurgical Design of Modern Linepipe Steels”

Proceedings of Conference Inclusions and Residuals in Steel, Ottawa, Ontario, March

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4-5, 1985 p119.[59] E. C. Hamre and A. M. Gilroy Scott, “Properties of Acicular -Ferrite Steel for Large

Diameter Linepipe”, Proc. Microalloying 75 Oct 1 -3, 1975, Washington, DC.[60] W. J. Fazackerley, P. A. Manuel and L. Christensen “First X -80 HSLA Pipeline in the

USA”, Proc. International Symposium on Microalloyed Steels for the Oil and GasIndustry, Araxa, MG, Brasil, January 23-26, 2006. Published by TMS.