Pressure Systems Certification Layered Pressure Vessel ... · ” each and 8 layers at 9/32” each...

Pressure Systems Certification Layered Pressure Vessel Acoustic Emission (AE)

Attenuation Study

Report #: PVS-16-008

Prepared by:

Claud Wyatt P. Hunter June 22, 2016

Jacobs ESSSA Group 1500 Perimeter Parkway, Suite 400 Huntsville, AL 35806

George C. Marshall Space Flight Center

Engineering & Science Services

& Skills Augmentation

Contract NNM12AA41C

NASA Marshall Space Flight Center, Huntsville, AL

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1.0 Summary

Jacobs ESSSA Group performed an Acoustic Emission (AE) attenuation study on layered

pressure vessel (LPV) V0269 in April 2016. Vessel V0269 is an in-service horizontal LPV

located at Building 4751 High Pressure Air Storage, Marshall Space Flight Center, Huntsville,

AL. This work was not performed to identify vessel defects or determine vessel fitness for

service but instead to collect acoustic signal attenuation data to help validate current MSFC

AE test sensitivity. As depicted in Figure 1, AE attenuation is the rate of decrease of ultrasonic

wave energy when propagating in a medium. For pressure vessel AE testing, attenuation is a

function of material properties including material hardness and Young’s modulus which in

turn are dependent on factors such as heat treatment, grain size, crystal structure, porosity,

elastic hysteresis. Also geometric factors such as friction between layers and layer thickness

will play a factor in the overall attenuation.

1.1 History

In October 2012, an entry into MSFC LPV V0343 was performed to collect AE data for

assessment of vessel acoustic sound path and shell layer attenuation in an effort to validate

the MSFC AE test procedure (Jacob’s ESSSA Group, Nondestructive Examination, Acoustic

Emission Testing of Multi-Layered Pressure Vessels at MSFC). AE sensors were installed

on the outer vessel and lead breaks were performed on the inner vessel to measure acoustic

signal strength through the vessel wall. It was confirmed from this testing that sound did

travel directly through the shell layers and that there was a significant signal attenuation (~30

dBAE) through the vessel wall. Due to time constraints for having V0343 out of service, this

first attenuation assessment was very cursory using a limited number of AE channels and was

only performed at one circumferential location on the vessel. Reference Appendix A for

additional details on V0343 sound path study.

Vessel V0269 presented an opportunity to perform a more detailed study of acoustic signal

attenuation on a large LPV. A confined space entry was again conducted to perform lead

breaks on the inner vessel wall with AE sensors on the outer wall. V0269 is a 5000 psig

1250 cubic foot vessel manufactured by Chicago Bridge and Iron (CB&I) in 1963. The

vessel was built with a 15/32” inner liner (MLP 1143 material) and 14 overwraps, 6 layers at

” each and 8 layers at 9/32” each (MLP 1146 material), for a total wall thickness of 4.293”

which also includes 1/16” corrosion allowance.

Figure 1 – Sound Wave Attenuation


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2.0 Objective

The attenuation study on V0269 will help identify sensor spacing requirements for future AE

testing and assist in calibration of location software for similar sized layered vessels. The

MSFC AE test procedure will be revised based on lessons learned from this study.

2.2 Test Equipment and Setup

AE INSTRUMENTATION MFR.: PHYSICAL ACOUSTICS CORP. (PAC)

AE INSTRUMENTATION TYPE: PAC DiSP System

AE EQUIPMENT CALIBRATION DUE: August 31, 2016 Certificate No:006175

SENSOR TYPE: R15I

RESONANT FREQ.: 150kHz

PREAMP TYPE: Integral to Sensor

FILTER: 100 - 400 kHz

SENSOR COUPLANT: Silicon grease

SENSOR ATTACHMENT METHOD: PAC Magnetic Hold-downs

2.3 Instrument Set-Up Parameters

DETECTION THRESHOLD 30dBAE

PREAMP GAIN: 40dB

SENSOR TYPES: R15I

INSTRUMENT GAIN: 20dB

REARM TIME/HLT 100 us

RISE TIME/ PDT 50 us

SINGLE CHANNEL TIME OUT: 100 us

2.4 Test Procedure

Vessel V0269 was instrumented with 20 R15I sensors, as shown in Figure 2, which were held

in place with magnetic hold-downs on the outside surface. AE sensors were spaced

circumferentially at 90 degrees apart (4.5 ft. intervals on y-axis) and at 5 ft. row intervals along

the vessel longitudinal (x) axis as shown Figure 2. The current MSFC AE test procedure of 10

ft. sensor row spacing was reduced to 5 ft. for this study based on tentative predictions derived

from the V0343 study. Lead breaks were performed with Pentel 0.3mm 2H mechanical pencil

leads on both the inner and outer vessel walls to provide the emission source for the signal

attenuation study. The current MSFC AE test procedure calls for a 40 dBAE detection threshold

to get above background noise during pressurization however for this study a detection

threshold of 30 dBAE was used since the vessel was in a quieter mode without pressurization.

This allowed for enhanced signal detection over larger distances.


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2.4.1 Pencil Lead Breaks for Vessel Wall Attenuation

For each series of lead breaks, five lead breaks were first performed on the outer vessel

wall immediately adjacent to a sensor mounted on the north head-to-shell weld (See

location A, Figure 3). Next, five lead breaks were performed on the vessel inner wall

surface, starting at position B and then every 12” in a vessel longitudinal direction

toward the shell-to-shell weld (i.e., lead breaks between sensors 1 and 19, 2 and 20, 3

and 17 and 4 and 18).

The highest shell section attenuation measured for V0269 was on the west side of the

vessel measured at AE channel 4 and is shown in Figure 4A. The amplitudes in Figure

4A represent an average amplitude for five (5) pencil lead breaks at each lead break

location along the vessel wall. Except for point B, the distances shown in Figure 4A

use the “planar” measurements from Table 1. Point B uses the direct path through wall

thickness.

Figure 2: Sensor Layout for Vessel V0269


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Lead Break

Location

Planar Distance from

Sensor

Linear

Distance from Sensor

A 0” 0”

B 0” 4.293”

C 12” 12.7”

D 24” 24.4”

E 36” 36.3”

F 48” 48.2”

G 60” 60.2”

Table 1: Distance from AE Sensor to Lead Break Location

OD

ID B C E D

4.293” Vessel Wall Thickness

12” 12” 12” 12” F

AE Sensor A

Vessel Inner Surface

Vessel Outer Surface

Figure 3: Distance Measurements Along Inner Vessel Surface (Five lead breaks beginning at OD location A and then moving to ID location B and continuing every 12” in a

longitudinal location between the vessel head-to-shell weld and the shell-to-shell weld)

North

Shell-to-Shell Weld Head-to-Shell Weld

G 12”


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Figure 4A: Shell Attenuation Curve (AE CH 4 – West Side of Vessel)

Figure 4B: Amplitude vs. Time for Shell Attenuation Curve (AE Channel 4)


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2.4.2 Pencil Lead Breaks for Shell Layer Attenuation

Prior to the attenuation tests performed on V0269, only outer surface attenuation curves

were available to provide AE sensor spacing guidance for the layered vessel shell

section. It was suspected that spacing guided by these curves may not be adequate for

the larger layered vessels due to the attenuation observed in vessel V0343 (Section 1.1).

Figure 5 shows a representative (typical) attenuation curve generated by lead breaks on

a layered vessel outside surface. Using guidance from Figure 5, the resulting sensor

row spacing would be approximately 10 ft. for multi-channel source location as shown

in Figure 6. However, using guidance from lead breaks on the vessel inner surface,

sensor row spacing would need to be less than 57” (4.75’) for a 40dBAE detection

threshold. Figure 7 shows a 4ft. AE sensor row spacing for comparison purposes.

Figure 5: Typical Layered Vessel Attenuation Using Outside Surface Lead Breaks Only


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Figure 6: Sensor Spacing Guided by Outer Surface Lead Breaks (Figure 5)

Figure 7: Sensor Spacing Guided by Inner Surface Lead Breaks (Figure 4A)

1

11

10

9

12

7

6

5

8

2

3

4 Can Section 20 ft.

10 ft.

4.5

ft

.

Denotes opposite side sensor channel


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2.4.3 Pencil Lead Breaks for Vessel Weld Attenuation

Four AE sensors 90 degrees apart were installed on both the vessel shell-to-shell and head-to-

shell weld (reference Figure 2). Five lead breaks were first performed on the outer vessel

wall immediately adjacent to a weld sensors 3 and 17. Five lead breaks were then performed

directly below each sensor on the vessel inner wall and at 12” circumferential intervals along

the weld on the vessel interior (distance measured along the curvature of the vessel wall).

Lead breaks were performed on the inner surface directly on the circumferential welds and

also in the heat affected zone (HAZ) on each side of the head-to-shell and shell-to-shell weld

(see Figure 8).

Attenuation curves for the circumferential welds are shown in the following pages. The

amplitudes represent the measured signal amplitude averaged over five (5) lead breaks at each

lead break location. The distances for the weld attenuation are measured along the inner

surface of the vessel as indicated by Figure 9.

Figure 8. Typical Location of Lead Breaks on Welds and HAZ

HAZ HAZ

Weld

Centerline


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2.5 Head to Shell Weld Attenuation Curve (North HAZ)

Distances shown below are between sensor and location of lead break shown are rounded. dB levels are

averaged over each 5 lead breaks per location.

AE Sensor

Outer Vessel Wall

Inner Vessel Wall

A

B C D

E

12” 12”

12”

ddf

Figure 9: Lead Breaks Performed Along Vessel Circumferential Welds

(12” intervals measured along inner vessel surface)

R=301/8”

4.293”


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Figure 10A: Attenuation Curve for Head-to-Shell Weld (North HAZ)

Figure 10B: Amplitude vs. Time for Head-to-Shell Weld (North HAZ)


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Figure 11A: Attenuation Curve for Head-to-Shell Weld (South HAZ)

Figure 11B: Amplitude vs. Time for Head-to-Shell Weld (South HAZ)


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Figure 12A: Attenuation Curve for Head-to-Shell Weld (Center of Weld)

Figure 12B: Amplitude vs. Time for Head-to-Shell Weld (Center of Weld)


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Figure 13B: Amplitude vs. Time for Shell-to-Shell Weld (North HAZ)

Figure 13A: Attenuation Curve for Shell-to-Shell Weld (North HAZ)


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Figure 14A: Attenuation Curve for Shell-to-Shell Weld (South HAZ)

Figure 14B: Amplitude vs. Time for Shell-to-Shell Weld (South HAZ)


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Figure 15A: Attenuation Curve for Shell-to-Shell Weld (Center of Weld)

Figure 15B: Amplitude vs. Time for Shell-to-Shell Weld (Center of Weld)


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2.4.4 Attenuation Tests Summary

Attenuation data for the V0269 shell section, shown in Figure 4A, indicates that a

sensor row spacing (x-axis) should be less than 57 inches for a 40 dB detection

threshold (test and evaluation threshold).

Worst case attenuation data for the circumferential welds, shown in Figure 13A,

indicates that a circumferential sensor spacing (y-axis) of approximately 48 inches is

required for a 40 dB detection threshold (test and evaluation threshold).

2.5 AE Source Location

ASME BPV Code Section V, Article 12, T-1265.2 requires sensors to be located so that a

lead break at any location in the examination area can be detected by the minimum number

of sensors required for the location algorithm. Lead breaks on V0269 were used to test the

location algorithms (XY Linear and 3D cylinder) ability to locate an AE source on a layered

vessel. Five lead breaks were performed beginning 12” longitudinally from channels 2 and 4

and continuing every 12” for 19 ft. All lead breaks were detected by the source location

algorithm when using a 30 dBAE threshold. However, the minimum test threshold amplitude

of 40 dBAE required by the MSFC AE test procedure was not obtained for each lead break.

Figures 16 and 17 show the detection and location of the lead breaks performed for the

source location test as calculated by the location algorithms. The hits shown within green

boxes are lead breaks detected and located by the location algorithms. Note that the green

boxes are automatically drawn by the location software but not all lead breaks detected are

within the green boxes. All lead breaks are verified by signal characteristics. The following is

a summary of the results of the source location test.

Head to Shell Weld (XY Linear)

15 lead breaks were performed at channel 3. Of these 15 lead breaks, 11 had amplitude

readings of 40dBAE or more at channel 2 (examination area).

Shell to Shell Weld (XY Linear)

15 lead breaks were performed at channel 17. All had amplitude readings of 40dBAE or

more at channel 20 (examination area).

Shell (west, triangle 3D)

5 lead breaks were performed beginning 12” from channel 4 and repeated every 12”

longitudinally for 19 feet for a total of 95 lead breaks. Of these 95 lead breaks, 88 had

amplitude readings of 40 dBAE or more.


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Figure 16: Results of Location Algorithm Showing Lead Breaks Beginning at Channel 2.

(Reference Figure 2 for sensor locations)

Figure 17: Results of Location Algorithm Showing Lead Breaks Beginning at Channel 4.

(Reference Figure 2 for sensor locations)


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3.0 Conclusion

Initially, the results of this study appear promising and show that AE from a source can be

transmitted from a vessel inner liner through the layers of pressure vessel and be detected and

located with acceptable accuracy. However, the data from the attenuation curves and source

location reveal the need to increase test sensitivity by decreasing sensor spacing. A proposed

sensor layout for a typical MSFC 1250 cubic foot (6’ diameter x 60’ long) layered vessel is

shown in Appendix B. The sensor layout shows a circumferential sensor spacing of 3.6 ft. (y-

axis) and a sensor row spacing of 4’ (x-axis). The proposed sensor spacing should allow

adequate AE test sensitivity for a 40dB detection threshold on the larger layered vessels but

would require 86 sensors (channels) which is beyond the current limits of the MSFC AE

equipment which has 56 channels. MSFC has many smaller layered vessels which would

require fewer AE channels to maintain the same or even greater test sensitivity.

4.0 Recommendation

Additional attenuation studies should be performed in the future on other similar sized layered

vessels to confirm results from the V0269 study or to verify the improved sensitivity when

using additional sensors and tighter sensor spacing as shown in Appendix B. MSFC layered

vessel V0023, which is scheduled for AE testing and cutup for material testing in the fall of

2016, may offer another opportunity for collecting attenuation data once the vessel is cut to

allow access to the vessel interior.


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Appendix A

AE hit below is the 2nd ID lead break at channel 8, OD sensor calibration read 85dBAE, total thru

wall loss is 34db. AE hit traveled thru the layers to reach Channel 8 first.

Manway

2

3

Denotes opposite side sensor channel

MSFC V343 AE SOUND PATH STUDY

0.3mm 2H lead breaks performed on inside surface 10 ft. from circ. weld C1 (midway between C1 and C2, adjacent to

sensor channels 6, 7, 8 and 9)

OD of circ. weld C2 ground smooth at sensor locations to facilitate coupling between sensor and vessel

AE data file: V343A.dta

C2 C1

20’-0”

7

5

4

6

8

9

X

10’-0”


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Appendix B

Sensor Layout for a MSFC 1250 Cubic Foot Layered Vessel

Increase sensitivity by decreasing vessel sensor spacing:

- 4 ft. spacing down the length of shell (X axis)

- 3.6 ft. spacing around the circumference (Y axis)

- Smaller layered vessels will maintain these distances with fewer channels

Pressure Systems Certification Layered Pressure Vessel ... · ” each and 8 layers at 9/32” each...

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