Effects of Notch Type and Loading Rate on CTOA of Modern X65 and X70 Pipe Steels

2014 ◽  
Author(s):  
S. Xu ◽  
J. Sollen ◽  
J. Liang ◽  
R. Zavadil ◽  
W. R. Tyson
Keyword(s):  
Loading Rate ◽  
Large Diameter ◽  
Test Method ◽  
Opening Angle ◽  
Pipe Steels ◽  
Drop Weight Tear Test ◽  
X65 Steel ◽  
Rotation Factor ◽  
Crack Tip Opening

The crack-tip opening angle (CTOA) has been investigated as a fracture propagation resistance parameter for prevention of fast ductile fracture in gas pipelines. A CANMET simplified single specimen CTOA method has been proposed as a mill test and is being applied to characterize critical CTOA (CTOAc) of typical pipe steels to develop a toughness database and improve the test method. In this work, tests using standard machined V-notch and API pressed notch (PN) drop-weight tear test (DWTT) specimens at quasi-static and impact rates were performed on modern X65 and X70 pipe steels typical of those used for CO2 pipelines. The rotation factor of the X65 steel deduced from the deformed ligament geometry is equivalent to those of X70 to X100 steels. Pressed-notch DWTT specimens were successfully fractured in impact and yielded CTOAc values equivalent to those of V-notched specimens following the CANMET recommended practice for determination of CTOAc. The effect of loading rate on CTOAc between the quasi-static and impact rates (covering five orders of magnitude) is small or negligible, being within experimental scatter. This is in agreement with data in the CANMET database, except for a low-toughness X52 steel that showed an increase in CTOAc between quasi-static and impact loading rates. The effect of flattening on CTOAc was also investigated and is small or negligible for the large-diameter (at least 508 mm) pipes tested in this work. The results may be used to support and improve a proposed test method for determination of CTOAc being considered by an ASTM Task Group and currently being evaluated in a round-robin testing program.

scholarly journals Evaluation and instrumentation of the drop weight tear test

2012 ◽  
Vol 3 (1) ◽  
pp. 52-58
Author(s):  
S. Vervaet ◽  
W. De Waele
Keyword(s):  
High Strength ◽  
Test Method ◽  
Opening Angle ◽  
Safety Issues ◽  
Natural Gas Pipelines ◽  
Drop Weight Tear Test ◽  
Fracture Appearance ◽  
Oil And Natural Gas ◽  
Linepipe Steels ◽  
Crack Tip Opening

With the use of high strength and high toughness steels in the pipeline industry it has become necessary tobetter understand the factors which influence the reliability and integrity of oil and natural gas pipelines. TheDrop-Weight Tear Test (DWTT) is a common test method to determine the fracture appearance andfracture ductility of steel. Its fundamental purpose is to determine the appearance of propagating fracturesin steels over the temperature range where the fracture mode changes from brittle to ductile. But there arestill many subjects of discussion concerning which results must be obtained, in which manner they shouldbe obtained and how they should be interpreted. Is it still possible to deduce a shear appearance fromsamples which have such an abnormal fracture that they used to be discarded as invalid ? Could resultsfrom the DWTT be correlated with the Crack Tip Opening Angle (CTOA), which is particularly important forfinite element modelling ? What to think about methods such as the two specimen CTOA and the simplifiedsingle specimen method ? How severe is the effect of tunnelling in contemporary linepipe steels and howcan this be dealt with ? Many questions still remain and many aspects are still vague despite the correlatingecological, economical and safety issues. Therefore, there is a major necessity for further investigations.

Flow Behaviour and Ductile Fracture Toughness of a High Toughness Steel

2004 ◽  
Author(s):  
S. Xu ◽  
R. Bouchard ◽  
W. R. Tyson
Keyword(s):  
Flow Stress ◽  
Ductile Fracture ◽  
Tensile Tests ◽  
Test Method ◽  
Opening Angle ◽  
Absorbed Energy ◽  
Crack Propagation Resistance ◽  
High Toughness ◽  
Drop Weight ◽  
Drop Weight Tear Test

This paper reports results of tests on flow and ductile fracture of a very high toughness steel with Charpy V-notch absorbed energy (CVN energy) at room temperature of 471 J. The microstructure of the steel is bainite/ferrite and its strength is equivalent to X80 grade. The flow stress was determined using tensile tests at temperatures between 150°C and −147°C and strain rates of 0.00075, 0.02 and 1 s−1, and was fitted to a proposed constitutive equation. Charpy tests were carried out at an initial impact velocity of 5.1 ms−1 using drop-weight machines (maximum capacity of 842 J and 4029 J). The samples were not broken during the test, i.e. they passed through the anvils after significant bending deformation with only limited crack growth. Most of the absorbed energy was due to deformation. There was little effect of excess energy on absorbed energy up to 80% of machine capacity (i.e. the validity limit of ASTM E 23). As an alternative to the CVN energy, the crack tip opening angle (CTOA) measured using the drop-weight tear test (DWTT) has been proposed as a material parameter to characterize crack propagation resistance. Preliminary work on evaluating CTOA using the two-specimen CTOA test method is presented. The initiation energy is eliminated by using statically precracked test specimens. Account is taken of the geometry change of the specimens (e.g. thickening under the hammer) on the rotation factor and of the effect of strain rate on flow stress.

Determination of Brittle-to-Ductile Transition Temperatures of Large-Diameter TMCP Linepipe Steel With High Charpy Energy by Use of Modified West Jefferson Testing

2016 ◽  
Author(s):  
Y. Hioe ◽  
G. Wilkowski ◽  
M. Fishman ◽  
M. Myers
Keyword(s):  
Transition Temperature ◽  
Brittle Fracture ◽  
Large Diameter ◽  
Pipe Steels ◽  
Line Pipe ◽  
Brittle To Ductile Transition ◽  
Pipe Burst ◽  
Drop Weight Tear Test ◽  
Fracture Appearance ◽  
Shear Area

In this paper the results will be presented for burst tests from a Joint Industry Project (JIP) on “Validation of Drop Weight Tear Test (DWTT) Methods for Brittle Fracture Control in Modern Line-Pipe Steels by Burst Testing”. The JIP members for this project were: JFE Steel as founding member, ArcelorMittal, CNPC, Dillinger, NSSMC, POSCO, Tenaris, and Tokyo Gas. Two modified West Jefferson (partial gas) pipe burst tests were conducted to assess the brittle-to-ductile transition temperature and brittle fracture arrestability of two 48-inch diameter by 24.6-mm thick X65 TMCP line-pipe steels. These steels had very high Charpy energy (350J and 400J) which is typical of many modern line-pipe steels. In standard pressed-notch DWTT specimen tests, these materials 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 makes the transition temperature difficult to determine. The shear area values versus temperature results for these two burst tests compared to various modified DWTT specimens are shown. Different rating methodologies; DNV, API, and a Best-Estimate of steady-state fracture propagation appearance were evaluated.

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