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Drop Weight Tear Testing
General Issues
A. Fonzo
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November 2013 Oil & Gas Business Area
Contents
Introduction
Materials selection for low temperature environment
DWTT specimens manufacturing
DWTT fracture appearance (regular or abnormal)
Historical basis of Battelle 85% Shear Area criterion
Current industry concerns
Open issues
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November 2013 Oil & Gas Business Area
Charpy V-Notched specimens may behave ductile but the pipe is brittle at the same temperature.
A full-thickness specimen (such as DWTT) predicts better the full scale pipe behavior.
DWTT, Drop Weight Tear Test (API RP 5L3) is used to investigate the conditions required for propagation of brittle/ductile fracture in line pipe (LP) and for measuring the LP material fracture appearance or fracture surface ductility.
The 85% shear area transition temperature Battelle criterion has been found to provide a good estimate of the full scale pipe’s FPTT.
The Submission to ISO TC67 SC2 WG16 is proposing an amendment of the ISO 3183, requiring that API PSL2 pipe be DWTT tested down to and including DN300 instead of the present cut-off of DN500.
This latter issue re-opened a series of issues to be investigated
Introduction
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November 2013 Oil & Gas Business Area
Outline
Introduction
Materials selection for low temperature environment
DWTT specimens manufacturing
DWTT fracture appearance (regular or abnormal)
Historical basis of Battelle 85% Shear Area criterion
Current industry concerns
Open issues
This document is confidential and is property of Centro Sviluppo Materiali SpA Any use, even if partial, should be agreed with Centro Sviluppo Materiali SpA
November 2013 Oil & Gas Business Area
Problem:
Selection of suitable material for service in artic environment
Approach:
Fracture mechanics testing (CVN, DWT, DWTT, Wide Plate) at low temperature according to recognized Standards and Recommendations (ASTM E208, API RP 5L3, etc.).
Full scale burst testing (the so called West Jefferson test) on linepipe cooled down to -50°C.
Results:
Nil Ductility Temperature determination, Charpy-V and DWTT brittle-to-ductile transition temperature determination on laboratory (specimen) and full scale (pipe) condition.
Materials Selection for Low Temperature environment
DWTT lab test @ low temp West Jefferson test @ low temp
Ductile fracture in a West Jefferson test
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November 2013 Oil & Gas Business Area
Instrumented DWTT machine @ CSM
Typical test outcome
Materials Selection for Low Temperature environment
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0.000 0.005 0.010 0.015
En
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kJ]
Lo
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N]
Time [s]
DAL-C-CG-01
Load Energy
Initiation of fracture propagation
Initiation energy
Applied Load
Total absorbed energy
This document is confidential and is property of Centro Sviluppo Materiali SpA Any use, even if partial, should be agreed with Centro Sviluppo Materiali SpA
November 2013 Oil & Gas Business Area
Outline
Introduction
Materials selection for low temperature environment
DWTT specimens manufacturing
DWTT fracture appearance (regular or abnormal)
Historical basis of Battelle 85% Shear Area criterion
Current industry concerns
Open issues
This document is confidential and is property of Centro Sviluppo Materiali SpA Any use, even if partial, should be agreed with Centro Sviluppo Materiali SpA
November 2013 Oil & Gas Business Area
Pressed notch
Chevron notch
DWTT specimen manufacturing
Manufacturing quality is important for results repeatability
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November 2013 Oil & Gas Business Area
Gull-Winged specimens (mandatory for pipe geometry with OD/WT<40, acc. API RP 5L3)
Pressed notch Chevron notch
DWTT specimen manufacturing
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November 2013 Oil & Gas Business Area
DWTT specimen manufacturing
Gull-wing shaped specimen configuration
Straight flattened specimen configuration
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November 2013 Oil & Gas Business Area
DWTT specimen manufacturing
This document is confidential and is property of Centro Sviluppo Materiali SpA Any use, even if partial, should be agreed with Centro Sviluppo Materiali SpA
November 2013 Oil & Gas Business Area
DWTT specimen manufacturing
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November 2013 Oil & Gas Business Area
ST-DWTT: standard pressed notchCN-DWTT: chevron notch, angle=60°
SCN-DWTT: slit chevron notch, angle=90
DWTT specimen manufacturing
Influence of notch on Transition Temperature
Source:
T. Kubo, et Al. “Quality Evaluation of Line Pipes by Chevron Notched Drop Weight Tear Test”, ISIJ International, Vol.35, No.4, pp.426-432, 1995
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November 2013 Oil & Gas Business Area
Outline
Introduction
Materials selection for low temperature environment
DWTT specimens manufacturing
DWTT fracture appearance (regular or abnormal)
Historical basis of Battelle 85% Shear Area criterion
Current industry concerns
Open issues
This document is confidential and is property of Centro Sviluppo Materiali SpA Any use, even if partial, should be agreed with Centro Sviluppo Materiali SpA
November 2013 Oil & Gas Business Area
Regular fracture of DWTT Differences in the Recommendations
According to API RP 5L3
According to DNV-OS-F101
ductile initiation under the notch is a matter of concern, especially for high upper shelf CVN energy steels
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November 2013 Oil & Gas Business Area
Regular fracture of DWTT
Notch
Brittle fracture
Shear fracture
Regular fracture – Valid tests
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November 2013 Oil & Gas Business Area
Inverse fracture Concern – Invalid tests
Notch
Brittle fracture
Shear fracture
Abnormal fracture of DWTT
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November 2013 Oil & Gas Business Area
Invalid tests according to API RP 5L3
Abnormal fracture of DWTT
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November 2013 Oil & Gas Business Area
Source:
R. Muraoka, et Al. “Evaluation for Abnormal Fracture Appearance in Drop Weight Tear Test with High Toughness
Linepipe”, OMAE2002-28183, Norway, 2002
Abnormal fracture of DWTT
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November 2013 Oil & Gas Business Area
Outline
Introduction
Materials selection for low temperature environment
DWTT specimens manufacturing
DWTT fracture appearance (regular or abnormal)
Historical basis of Battelle 85% Shear Area criterion
Current industry concerns
Open issues
This document is confidential and is property of Centro Sviluppo Materiali SpA Any use, even if partial, should be agreed with Centro Sviluppo Materiali SpA
November 2013 Oil & Gas Business Area
Source:
Maxey, W.A., Kiefner, J.F. and Eiber, R.J. “Brittle Fracture Arrest in Gas Pipelines”, PRCI Report No. L51436, April 1983.
Brittle fracture propagation is prevented by ensuring that a DWTT specimen exhibits 85% shear area on fracture surface (this ensures that the steel is operating on the upper shelf).
ISO 3183 85% shear area criterion
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November 2013 Oil & Gas Business Area
DWTT
Full Scale
85% SA
…but curves are fitted on very scattered data
ISO 3183 85% shear area criterion
Source:
Maxey, W.A., Kiefner, J.F. and Eiber, R.J. “Brittle Fracture Arrest in Gas Pipelines”, PRCI Report No. L51436, April 1983.
This document is confidential and is property of Centro Sviluppo Materiali SpA Any use, even if partial, should be agreed with Centro Sviluppo Materiali SpA
November 2013 Oil & Gas Business Area
DWTT fitting Full scale burst test fitting
Source:
Maxey, W.A., Kiefner, J.F. and Eiber, R.J. “Brittle Fracture Arrest in Gas Pipelines”, PRCI Report No. L51436, April 1983.
Data set is highly scattered: at the same temperature min and max Shear Area can differ by up to 0.5
Historical basis of 85% shear area criterion
This document is confidential and is property of Centro Sviluppo Materiali SpA Any use, even if partial, should be agreed with Centro Sviluppo Materiali SpA
November 2013 Oil & Gas Business Area
Outline
Introduction
Materials selection for low temperature environment
DWTT specimens manufacturing
DWTT fracture appearance (regular or abnormal)
Historical basis of Battelle 85% Shear Area criterion
Current industry concerns
Open issues
This document is confidential and is property of Centro Sviluppo Materiali SpA Any use, even if partial, should be agreed with Centro Sviluppo Materiali SpA
November 2013 Oil & Gas Business Area
If/How DWTT testing parameters can influence results and BDTT?
Influence of notch configuration on BDTT needs further investigation (the most representative notch choice seems to be pipe WT dependent)
DWTT specimen manufacturing problems (heavy-walled pipes, low OD/WT ratio)
Abnormal Fracture Appearance (AFA) in DWTT: ductile fracture initiation under the notch and inverse fracture invalidate QA tests
DWTT representativeness of full-scale results especially for modern steels (high Charpy-VN shelf energy)
Summary of current industry concerns
This document is confidential and is property of Centro Sviluppo Materiali SpA Any use, even if partial, should be agreed with Centro Sviluppo Materiali SpA
November 2013 Oil & Gas Business Area
Outline
Introduction
Materials selection for low temperature environment
DWTT specimens manufacturing
DWTT fracture appearance (regular or abnormal)
Historical basis of Battelle 85% Shear Area criterion
Current industry concerns
Open issues
This document is confidential and is property of Centro Sviluppo Materiali SpA Any use, even if partial, should be agreed with Centro Sviluppo Materiali SpA
November 2013 Oil & Gas Business Area
The influence of testing parameters should be better investigated and clarified (DWTT machine capacity, velocity at impact, etc).
Repeatability: the material fracture behavior in DWTT testing is affected by specimen preparation (flattening, notch type, etc) and geometry (thickness).
The type of specimen (straight flattened or gull-wing shaped) can affect the results especially on low OD/WT pipes.
Is it feasible to realize non-flattened specimens from heavy-walled pipes?
Ductile fracture initiation under the notch, especially for high toughness steels.
Reverse fracture is a DWTT test peculiarity (not present on line-pipes):
If inverse fracture occurs, the test is invalid
Influence on thickness and microstructure needs to be further investigated
How to account for reverse fracture remains an open issue:
Standards do not account for it (except DNV)
Many routes are currently followed while a unique criterion should be identified
Open Issues
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November 2013 Oil & Gas Business Area
PRCI (Pipeline Research Council International) research project MAT-8-1 Phase 1 Design Materials & Construction Technical Committee
Aim :
To develop methods that may allow the industry to better design safe gas pipelines made from modern steels
Outcome from Phase 1 (concluded) :
Criticalities of the DWTT and concerns with propagating cracks in gas pipelines made from modern steels with high upper-shelf Charpy Energy
Focus on sweet gas transmission pipelines with outer diameter over 12”, made from API X65, X70 and X80 steels
CSM Work for PRCI
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November 2013 Oil & Gas Business Area
Thank you for your attention!
Dr. Gianluca Mannucci Oil and Gas Business Area Director E-mail: [email protected] Phone +39 06 5055325
Dr. Andrea Fonzo Oil and Gas Business Manager E-mail: [email protected] Phone: +39 06 5055402
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