When Old Line Pipes Initiates Fracture in a Ductile Manner

2006 ◽  
Author(s):  
G. Wilkowski ◽  
D. Rudland ◽  
D. Rider ◽  
P. Mincer ◽  
W. Sloterdijk
Keyword(s):  
Transition Temperature ◽  
Ductile Fracture ◽  
Static Loading ◽  
Crack Depth ◽  
Temperature Shift ◽  
Charpy Impact ◽  
Pipe Material ◽  
Line Pipe ◽  
Strain Rate Effects ◽  
Constraint Effects

This paper presents a procedure to determine the lowest temperature that a ductile fracture will initiate in old (or new) pipe that behaves in a brittle manner (by Charpy testing). Over the last decade, much work has been done to assess constraint effects on the crack-driving force for specimens and cracks in pipes. The material’s transition temperature where the fracture process changes from ductile tearing to cleavage fracture at crack initiation is affected by the constraint conditions, but is a material property that cannot be determined analytically. This paper presents a methodology to account for constraint effects to predict the lowest temperature where ductile fracture initiation occurs and relates that temperature back to Charpy impact data for X60 and lower grades, particularly for older vintage linepipe materials. The method involves a series of transition temperature shifts to account for thickness effects, strain-rate effects, and constraint effects to give a master curve of transition temperatures from Charpy data to through-wall-cracked or surface-cracked pipes (with various surface-crack depth values) under quasi-static loading. These transition temperature shifts were based on hundreds of pipe tests and thousands of specimen tests over several decades of work by numerous investigators. Conducting tests on 1927 and 1948 vintage line-pipe steels subsequently validated this method. In addition, data were developed on the 1927 vintage pipe material to assess the effect of the bluntness of a corrosion flaw on the lowest temperature where ductile fracture will still occur under quasi-static loading. An addition transition temperature shift occurs as a function of the bluntness of the flaw.

Predicting the Brittle-to-Ductile Transition Temperatures for Surface Cracks in Pipeline Girth Welds: It’s Better Than You Thought

2008 ◽  
Author(s):  
Gery Wilkowski ◽  
David Rudland ◽  
Do-Jun Shim ◽  
David Horsley
Keyword(s):  
Transition Temperature ◽  
Surface Crack ◽  
Master Curve ◽  
Crack Depth ◽  
Temperature Shift ◽  
Transition Temperatures ◽  
Surface Cracks ◽  
Line Pipe ◽  
Brittle To Ductile Transition ◽  
Girth Welds

A methodology to predict the brittle-to-ductile transition temperature for sharp or blunt surface-breaking defects in base metals was developed and presented at IPC 2006. The method involved applying a series of transition temperature shifts due to loading rate, thickness, and constraint differences between bending versus tension loading, as well as a function of surface-crack depth. The result was a master curve of transition temperatures that could predict dynamic or static transition temperatures of through-wall cracks or surface cracks in pipes. The surface-crack brittle-to-ductile transition temperature could be predicted from either Charpy or CTOD bend-bar specimen transition temperature information. The surface crack in the pipe has much lower crack-tip constraint, and therefore a much lower brittle-to-ductile transition temperature than either the Charpy or CTOD bend-bar specimen transition temperature. This paper extends the prior work by presenting past and recent data on cracks in line-pipe girth welds. The data developed for one X100 weld metal shows that the same base-metal master curve for transition temperatures works well for line-pipe girth welds. The experimental results show that the transition temperature shift for the surface-crack constraint condition in the weld was about 30C lower than the transition temperature from standard CTOD bend-bar tests, and that transition temperature difference was predicted well. Hence surface cracks in girth welds may exhibit higher fracture resistance in full-scale behavior than might be predicted from CTOD bend-bar specimen testing. These limited tests show that with additional validation efforts the FITT Master Curve is appropriate for implementation to codes and standards for girth-weld defect stress-based criteria. For strain-based criteria or leak-before-break behavior, the pipeline would have to operate at some additional temperature above the FITT of the surface crack to ensure sufficient ductile fracture behavior.

Predicting the Brittle-to-Ductile Fracture Initiation Transition Temperature for Surface-Cracked Pipe From Charpy Data

2005 ◽  
Author(s):  
Gery Wilkowski ◽  
Dave Rudland ◽  
Richard Wolterman
Keyword(s):  
Transition Temperature ◽  
Ductile Fracture ◽  
Failure Modes ◽  
Charpy Impact ◽  
Fracture Initiation ◽  
Evaluation Procedures ◽  
Balance Of Plant ◽  
Constraint Effects ◽  
Impact Data ◽  
Ductile Fracture Initiation

Much work has been done to assess constraint effects on the crack-driving force for specimens and cracks in pipes. The material’s transition temperature where the fracture process changes from ductile tearing to cleavage fracture at crack initiation is affected by the constraint conditions, but is a material property that cannot be determined analytically. This paper presents a methodology to account for constraint effects to predict the lowest temperature for ductile fracture initiation and relates that temperature to Charpy impact data for typical ferritic pipe materials. It involves a series of transition temperature shifts to account for thickness, strain-rate, and constraint to give a master curve of transition temperatures from Charpy data to through-wall-cracked or surface-cracked pipes (with various a/t values) under quasi-static loading. These transition temperature shifts were based on hundreds of pipe tests and thousands of specimen tests over several decades of work by numerous investigators. It is equally applicable to ferritic nuclear pipe for Class 2, 3, or balance of plant piping, or for older linepipe materials. If found to be reasonable, then the procedure could be used in the ASME pipe flaw evaluation procedures as a screening criterion between LEFM and EPFM failure modes.

Predicting the Fracture Initiation Transition Temperature in High Toughness, Low Transition Temperature Line Pipe With the COD Test

1974 ◽  
Vol 96 (4) ◽  
pp. 330-334 ◽  
Author(s):  
R. J. Podlasek ◽  
R. J. Eiber
Keyword(s):  
Transition Temperature ◽  
Static Loading ◽  
Crack Opening ◽  
Fracture Initiation ◽  
Full Scale ◽  
Pipe Material ◽  
Opening Displacement ◽  
Line Pipe ◽  
High Toughness ◽  
Critical Flaw

This paper describes the use of the crack opening displacement (COD) test to predict the fracture initiation transition temperature of high toughness, low-transition temperature in line pipe. A series of COD tests using t × t and t × 2t specimens made from this line pipe material. The COD test was conducted over a range of temperatures and the point where the upper shelf COD values began to decrease with decreasing temperature was defined. To verify the full-scale significance of this temperature, a series of three experiments was conducted on 48-in. (1.22m) dia line pipe to bracket the transition temperature defined in the COD Test. The results suggest that the COD transition temperature can ve used to define the fracture initiation temperature for static loading in pipe. In addition, in the transition temperature region, the full-scale results, while limited in number, suggest that the COD values could possibly be used to predict the critical flaw sizes in the pipe material.

Effects of Soil Cohesiveness and Depth on Dynamic Ductile Fracture Speeds

2008 ◽  
Author(s):  
D. Rudland ◽  
D.-J. Shim ◽  
G. M. Wilkowski ◽  
S. Kawaguchi ◽  
N. Hagiwara ◽  
...  
Keyword(s):  
Ductile Fracture ◽  
Large Scale ◽  
Soil Depth ◽  
Crack Arrest ◽  
Small Scale ◽  
Total Density ◽  
Pipe Material ◽  
Pipe Steels ◽  
Line Pipe ◽  
Fracture Arrest

The ductile fracture resistance of newer line pipe steels is of concern for high grade/strength steels and higher-pressure pipeline designs. Although there have been several attempts to make improved ductile fracture arrest models, the model that is still used most frequently is the Battelle Two-Curve Method (TCM). This analysis incorporates the gas-decompression behavior with the fracture toughness of the pipe material to predict the minimum Charpy energy required for crack arrest. For this analysis, the influence of the backfill is lumped into one empirically developed “soil” coefficient which is not specific to soil type, density or strength. No attempt has been made to quantify the effects of soil depth, type, total density or strength on the fracture speeds of propagating cracks in line pipe steels. In this paper, results from small-scale and large-scale burst tests with well-controlled backfill conditions are presented and analyzed to determine the effects of soil depth and cohesiveness on the fracture speeds. Combining this data with the past full-scale burst data used in generating the original backfill coefficient provides additional insight into the effects of the soil properties on the fracture speeds and the arrest of running ductile fractures in line pipe materials.

Modified West Jefferson Burst Test for Assessment of Brittle Fracture Arrest in Thick-Wall TMCP Line-Pipe Steel With High Charpy Energy

2016 ◽  
Author(s):  
S. Igi ◽  
T. Sakimoto ◽  
J. Kondo ◽  
Y. Hioe ◽  
G. Wilkowski
Keyword(s):  
Transition Temperature ◽  
Brittle Fracture ◽  
Ductile Fracture ◽  
Base Metal ◽  
The Other ◽  
Line Pipe ◽  
Burst Test ◽  
Seam Weld ◽  
Shear Area ◽  
Fracture Arrest

Three partial gas pipe burst tests were conducted to assess the brittle-to-ductile transition temperature and brittle fracture arrestability of a heavy-walled TMCP line-pipe steel. This steel had a very high Charpy energy (400 J) which is typical of many modern line-pipe steels. In standard pressed-notch DWTT specimen tests this material exhibited abnormal fracture appearance (ductile fracture from the pressed notch prior to brittle fracture starting) that occurs with many high Charpy energy steels. Such behavior gives an invalid test by API RP 5L3, which makes the transition temperature difficult to determine. The first burst test was conducted in a manner that is typical of a traditional West Jefferson (partial gas vessel) burst tests. The crack was initiated in the center of the cooled vessel (with a partial air gap), but an unusual result occurred. In this test a ductile fracture just barely started from each crack tip, but one of the endcaps blew off. The pipe rocketed into the wall of a containment building. The opposite endcap impacted the wall of the building and brittle fractures started there with one coming back to the center of the vessel. The implication from this test was that perhaps initiation of the brittle fracture in the base metal gives different results than if the initial crack came from a brittle location. The second burst test used a modified West-Jefferson Burst Test procedure. The modification involved cutting a short length of pipe at the center of the vessel and rotating the seam weld to the line of crack propagation. The HAZ of the axial seam weld had a higher dynamic transition temperature. The initiation flaw was across one of the center girth welds so that one side of the initial through-wall crack had the crack tip in the base metal while the other side initiated in the seam weld HAZ. On the base metal side, the crack had about 220 mm of crack growth before reaching steady-state shear area, i.e., the shear area gradually decreased as the fracture speed was increasing. On the other side, a brittle fracture was started in the HAZ as expected, and once it crossed the other central girth weld into the base metal, the fracture immediately transformed to a lower shear area percent. These results along with those from the first burst test suggest that the DWTT specimen should have a brittle weld metal in the starter notch region to ensure the arrestability of the material. The final burst test was at a warmer temperature. There was a short length of crack propagation with higher shear area percent, which quickly turned to ductile fracture and arrested. In addition various modified DWTTs were conducted and results were analyzed using an alternative brittle fracture arrest criterion to predict pipe brittle fracture arrestability.

To Determination of the WWER RPV Steels Crack Resistance Characteristics

2013 ◽  
Author(s):  
Igor Orynyak ◽  
Maksym Zarazovskii ◽  
Sergii Radchenko ◽  
Volodymyr Kozlov
Keyword(s):  
Fracture Toughness ◽  
Transition Temperature ◽  
Crack Resistance ◽  
Temperature Shift ◽  
Charpy Impact ◽  
Temperature Range ◽  
Pressurized Thermal Shock ◽  
Reactor Pressure ◽  
15Kh2nmfa Steel

The efficiency of fracture toughness determined by the methodology of normative document PNAE G-7-002-86 has been analyzed. Crack resistance characteristics of WWER-1000 reactor pressure vessel base metal at unirradiated condition are obtained by experimental way. All specimens were made of the RPV support forging (15Kh2NMFA steel) of abandoned Crimean NPP Fracture toughness experiments were carried out on three types of specimens CT 1T, CT 0.5T and SEB over a temperature range from −130°C to −40°C in fully accordance to the ASTM E1921. Charpy impact energy data obtained on twelve specimens over a temperature range from −80°C to 80°C has been used to determine the 47J transition temperature. Comparison of obtained fracture toughness data with normative curve shows that the last one has unreasonably high lower shelf. It has been found that the PNAE G-7-002-86 Code, which uses the ideology of transition temperature shift, is too conservative to estimate WWER-1000 RPVs resistance against brittle fracture for the pressurized thermal shock (over 90 MPa·√m area of stress intensity factor).

The Effects of Soil Properties on the Fracture Speeds of Propagating Axial Cracks in Line Pipe Steels

2006 ◽  
Author(s):  
D. Rudland ◽  
G. Wilkowski ◽  
B. Rothwell
Keyword(s):  
Moisture Content ◽  
Ductile Fracture ◽  
Soil Type ◽  
Small Diameter ◽  
Valuable Insight ◽  
Total Density ◽  
Pipe Material ◽  
Pipe Steels ◽  
Line Pipe ◽  
Fracture Arrest

The ductile fracture resistance of newer line pipe steels is of concern for higher grade/strength steels and higher-pressure pipeline designs. Although there have been several attempts to make improved ductile fracture arrest models, the model that is still used most frequently is the Battelle Two-Curve Ductile Fracture Arrest Model, which incorporates the gas-decompression behavior with the fracture toughness of the pipe material to predict the minimum Charpy energy required for crack arrest. For this model, the effect of backfill on the propagating crack fracture speeds is lumped into one empirically based “backfill coefficient,” which does not distinguish different soil types or strengths. Some modifications to this backfill coefficient have been proposed for frozen soil as a function of moisture content, and for water backfill for offshore applications, but no attempt has been made to quantify the effects of soil type, total density or strength on the fracture speeds of propagating cracks in line pipe steels. This paper presents the results from a series of small diameter pipe burst tests that were conducted with different soil backfills. The soils’ moisture content, density, and strength were fully characterized in situ and in the laboratory. In addition, fracture speed data in both unbackfilled and backfilled conditions were recorded. The comparison of the change in fracture speed as a function of soil type, moisture and strength gives valuable insight into the effects of soil on the arrest of running ductile fractures in line pipe materials.

Crack Arrest Testing of High Strength Steels

2012 ◽  
Author(s):  
Andre Hasenhütl ◽  
Marion Erdelen-Peppler ◽  
Christoph Kalwa ◽  
Martin Pant ◽  
Andreas Liessem
Keyword(s):  
Crack Initiation ◽  
Ductile Fracture ◽  
Impact Energy ◽  
Fracture Propagation ◽  
Charpy Impact ◽  
Impact Testing ◽  
Charpy Impact Energy ◽  
Line Pipe ◽  
Test Standards ◽  
Charpy Impact Testing

Fracture propagation is a major concern for the safe operation of gas transmission pipelines. Ductile fracture resistance, which is required according to line pipe standards, is commonly assessed by Charpy impact testing. If fracture occurs during pipe operation, fracture propagation is required to appear in ductile manner. The prerequisite for this is the demonstration of sufficient shear fracture in the BDWT test and minimum required Charpy impact energy. A combination of both requirements ensures avoidance of brittle fracture as well as control of ductile fracture propagation. The experimental chain of evidence and the Battelle-Two-Curve (BTC) model which is the most widely applied model to predict resistance against fracture propagation have been developed on basis of welded pipes of grade ≤ X70. The model has been calibrated against test data obtained from pipes with Charpy impact energy values below 100 J. In recent years, new material concepts were developed to increase material strength and material toughness. On the one hand, increase in material toughness, which is evaluated by Charpy impact testing, is often achieved by an increase in crack initiation resistance. On the other hand, crack propagation resistance, which is determined by BDWT testing with an instrumented striker, can remain on the same level. Increased material toughness and crack initiation resistance can be manifested by incomplete fracture of Charpy impact specimens in the upper shelf (ductile fracture). Actual Charpy impact test standards for metallic materials do not coincide with each other regarding the validity of Charpy energy of unbroken specimens. Increased crack initiation resistance also affects fracture initiation mechanism in BDWT tests, leading to invalid test results according test standards. Invalidity can be expressed by inverse fracture appearance. To avoid inverse fracture, crack initiation energy can be reduced by changing notch type and therefore changing the constraint in the root of the notch. BDWT test standards also do not agree with each other concerning allowable notch types. While the pressed notch type is the preferred one for low toughness steels and the Chevron notch type for higher toughness steels according some test standards, other test standards allow only for a pressed notch type. Being semi-empirical by nature, the BTC concept strongly depends on the input parameters derived from different material tests. Changing test conditions can have a direct impact on the assessment results.

Crack in Corrosion Defect Assessment in Transmission Pipelines

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
A. Hosseini ◽  
D. Cronin ◽  
A. Plumtree
Keyword(s):  
Crack Depth ◽  
Evaluation Criteria ◽  
Average Error ◽  
Failure Behavior ◽  
Pipe Material ◽  
Line Pipe ◽  
Collapse Pressure ◽  
Defect Assessment ◽  
Level 3 ◽  
Corrosion Defects

Cracks may occur coincident with corrosion representing a new hybrid defect in gas and oil pipelines known as crack in corrosion (CIC) that is not directly addressed in the current codes or assessment methods. Hence, there is a need to provide an assessment of CIC and evaluate the line integrity, as well as identify the requirements for defect repair or line hydrotest. An experimental investigation was undertaken to evaluate the collapse pressures of lines containing corrosion, cracks, or (CIC) defects in a typical line pipe (API 5L Grade X52, 508 mm diameter, 5.7 mm wall thickness). The mechanical properties of the pipe were measured using tensile, Charpy, and J-testing for use in applying evaluation criteria. Rupture tests were undertaken on end-capped sections containing uniform depth, finite length corrosion, cracks, or CIC defects. Failure occurred by plastic collapse and ductile tearing for the corrosion defects, cracks, and CIC geometries tested. For the corrosion defects, the corroded pipe strength (CPS) method provided the most accurate results (13% conservative on average). The API 579 (level 3 failure assessment diagram (FAD), method D) provided the least conservative collapse pressure predictions for the cracks with an average error of 20%. The CIC collapse pressures were bounded by those of a long corrosion groove (upper bound) and a long crack (lower bound), with collapse dominated by the crack when the crack depth was significant. Application of API 579 to the CIC provided collapse pressure predictions that were 18% conservative. Sixteen rupture tests were successfully completed investigating the failure behavior of longitudinally oriented corrosion, crack, and CIC. The pipe material was characterized and these properties were used to predict the collapse pressure of the defects using current methods. Existing methods for corrosion (CPS) and cracks (API 579, level 3, method D) gave conservative collapse pressure predictions. The collapse pressures for the CIC were bounded by those of a long corrosion groove and a long crack, with collapse dominated by the crack when the crack depth was significant. CIC failure behavior was determined by the crack to corrosion depth ratio, total defect depth and its profile. The results showed that the failure pressures for CIC were reduced when their equivalent depths were similar to those of corrosion and using crack evaluation techniques provided an approximate collapse pressure.

Assessment of Corrosion Defects in Old, Low Toughness Pipelines

2006 ◽  
Author(s):  
Michael Martin ◽  
Robert (Bob) Andrews ◽  
Vinod Chauhan
Keyword(s):  
Transition Temperature ◽  
Transition Region ◽  
Assessment Methods ◽  
Transition Curve ◽  
Metal Loss ◽  
Pipe Material ◽  
Regulatory Requirements ◽  
Line Pipe ◽  
Corrosion Defects ◽  
Dependent Failure

Corrosion metal loss in one of the major damage mechanisms to transmission pipelines worldwide. The remaining strength of corroded pipe subjected to internal pressure loading has been extensively researched and guidelines for assessing corrosion are well defined. Methods including ASME B31G, RSTRENG and LPC have been developed, validated and matured to the extent that they are now incorporated in standards and regulatory requirements. However, these methods are based on the assumption that the pipe fails via a ductile mechanism, i.e., the line pipe material has sufficient toughness to prevent a toughness dependent failure. This limits the application of the existing methods to materials that have sufficient toughness. It is possible that some older pipelines operate with the material in the ductile / brittle transition region of the Charpy transition curve, or even on the lower shelf. It is also possible that under fault conditions, a pipeline normally operating on the upper shelf could be temporarily in the transition region. In these circumstances, existing assessment criteria may be non-conservative. At present there are no rigorous criteria available for assessing corrosion defects in low toughness pipe. This paper presents an approach for removing the uncertainty in the use of existing methods for assessing corrosion defects in older, low toughness pipelines based on the Beremin approach to brittle cleavage fracture. Comparison of the Beremin results with existing assessment methods allows an ‘effective transition temperature’ to be defined as the temperature at which the existing method is no longer conservative. The results suggest that, for the corrosion defects investigated, the effective transition temperature is sufficiently low that existing assessment methods will remain conservative.

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