Effects of Prestrain on Fracture Toughness and Fatigue-Crack Growth of Line Pipe Steels

2000 ◽  
Author(s):  
Naoto Hagiwara ◽  
Tomoki Masuda ◽  
Noritake Oguchi
Keyword(s):  
Fatigue Crack ◽  
Transition Temperature ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Initiation ◽  
Pipe Steels ◽  
Crack Tip Opening Displacement ◽  
Line Pipe ◽  
Brittle Transition ◽  
Ductile To Brittle Transition

To investigate the failure mechanism of pipelines subjected to mechanical damage, Charpy impact, crack-tip-opening displacement (CTOD) and fatigue-crack growth tests were carried out for six series of line pipe steels with uniaxial plastic prestrain, εpr. The Charpy absorbed energy and critical CTOD (δc) decreased with increasing |εpr|; ln δc = α εpr + β. The derivative, dδc/dεpr, was dependent on the ductile-to-brittle transition temperature of the steels. In the CTOD tests, the prestrain caused ductile-to-brittle transition for the steels with a higher transition temperature. The effects of the compressive εpr on both the reduction of δc and ductile-to-brittle transition were larger than those of the tensile εpr. The compressive εpr accelerated both the fatigue-crack initiation and growth.

Effects of Prestrain on Fracture Toughness and Fatigue-Crack Growth of Line Pipe Steels

2001 ◽  
Vol 123 (3) ◽  
pp. 355-361 ◽  
Author(s):  
Naoto Hagiwara ◽  
Tomoki Masuda ◽  
Noritake Oguchi
Keyword(s):  
Fatigue Crack ◽  
Transition Temperature ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Initiation ◽  
Fatigue Properties ◽  
Uniaxial Tensile ◽  
Pipe Steels ◽  
Line Pipe ◽  
Brittle Transition

Crack-tip-opening displacement (CTOD) and fatigue-crack growth tests were conducted for several line pipe steels with uniaxial tensile or compressive prestrain, εpr. Critical CTOD decreased with increasing |εpr|. The reduction of critical CTOD due to prestrain was dependent on the ductile-brittle transition temperature of the steels without prestrain. A few percent of εpr induced the ductile-brittle transition for the steels with a higher transition temperature. The compressive εpr had larger effects on both reduction of critical CTOD and strain induced ductile-brittle transition than the tensile εpr. Only the high compressive εpr accelerated both fatigue crack initiation and growth, and no obvious effect of the tensile εpr on the fatigue properties was observed.

Effect of Sour Acidizing Treatments on the Fatigue Crack Growth and Fracture Toughness Behavior of C-Mn Line Pipe Steels

2016 ◽  
Author(s):  
Weiwei Yu ◽  
Jonathan Bowman ◽  
Apurva Batra ◽  
Ramgopal Thodla ◽  
Colum Holtam ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Compact Tension ◽  
Pipe Steels ◽  
Production Environment ◽  
Line Pipe ◽  
Fatigue And Fracture ◽  
Girth Welds

Acidizing treatments are typically performed intermittently during the life of a well. However, more recently there has been a desire to perform an increased number of acidizing treatments in order to improve production. The acidizing treatments typically involve highly corrosive acids, such as hydrofluoric (HF), hydrochloric (HCl) and acetic acid, which are known to cause significant corrosion. In the presence of hydrogen sulfide (H2S), these acidizing treatments could cause environmentally assisted fatigue and fracture (i.e. increased fatigue crack growth rates and reduced fracture toughness). A test program is underway to evaluate and quantify the effect of sour acidizing treatments on the fatigue and fracture behavior of welded C-Mn line pipe steels. This paper describes the preliminary findings from fatigue crack growth rate (FCGR) and fracture toughness (FT) tests on as-welded (i.e. unstrained) pipe. All tests were conducted at room temperature (RT) using compact tension (CT) specimens notched in the parent pipe (PP). Frequency scan FCGR tests were performed in the following sour acid conditions: simulated production environment (PE), spent acid without inhibitor and spent acid with residual corrosion inhibitor. The PE consisted of a simulated brine with pH = 4.5 and partial pressure of H2S (pH2S) = 0.21psia. FCGRs in the sour PE were of the order of 20 times faster than in air. The pH2S was the same for the tests in spent acid environments, but the pH was lower (approximately 3.5). As would be expected, the FCGRs were much higher in the low pH environment. The highest FCGRs were observed in the inhibited sour spent acid environment and were up to 100 times faster than in air. Sour FT tests were also conducted in the PE and in spent acid with and without inhibitor. In all cases, the measured FT values were significantly lower than in air. The test in PE exhibited higher FT than in the sour acidizing environment. The lowest FT values were observed in spent acid with inhibitor. Future work will investigate the effect of reeling on the fatigue and FT performance of pipe girth welds in sour acidizing environments.

Effect of Acidizing Treatments on the Fatigue Crack Growth Behavior of C-Mn Line Pipe Steels

2016 ◽  
Author(s):  
Apurva Batra ◽  
Jonathan Bowman ◽  
Weiwei Yu ◽  
Ramgopal Thodla ◽  
Colum Holtam ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Elevated Temperature ◽  
Fatigue Crack Growth ◽  
Corrosion Inhibitor ◽  
Crack Growth ◽  
Crack Closure ◽  
Pipe Steels ◽  
Line Pipe ◽  
Corrosion Rates ◽  
Frequency Scan

Acidizing treatments are typically performed intermittently during the life of a well. However, more recently there has been a desire to perform an increased number of acidizing treatments in order to improve production. The acidizing treatments typically involve highly corrosive acids, such as hydrofluoric (HF), hydrochloric (HCl) and acetic acid, which are known to cause significant corrosion, but could also lead to environmentally assisted fatigue and fracture. A study was performed to evaluate the effect of acidizing treatments on the fatigue behavior of welded C-Mn line pipe steels. This paper describes the results of fatigue crack growth rate (FCGR) tests on as-welded (i.e. unstrained) pipe. FCGR tests were conducted at room temperature (RT) in three different acid conditions: fresh acid with corrosion inhibitor, spent acid with corrosion inhibitor and spent acid without corrosion inhibitor. Frequency scan FCGR tests were performed on compact tension (CT) specimens notched in the parent pipe (PP), heat affected zone (HAZ) and weld centerline (WCL). The FCGRs in all three environments were higher than in air and exhibited a frequency dependence. Tests in fresh acid with inhibitor exhibited plateau FCGR values around 20–30 times higher than in air. Tests in spent acid with inhibitor exhibited a strong frequency dependence with plateau FCGR values approximately 80–100 times higher than in air. In spent acid without inhibitor, the plateau FCGR was around 20 times higher than in air, however at the lowest frequencies the FCGR decreased, most likely due to crack closure/blunting effects. This behavior is consistent with the higher corrosion rate in this uninhibited environment. The role of corrosion products in causing crack closure/blunting was further evidenced in tests performed at elevated temperature (165°F / 74°C), where the FCGR at 1Hz was significantly higher than at RT. The plateau FCGR in fresh acid and spent acid with inhibitor was approximately 40–50 times higher than in air, but the FCGR decreased at lower frequency. This is similarly believed to be due to the higher corrosion rates at elevated temperature causing crack closure/blunting. The FCGR in spent acid without inhibitor at 165°F (74°C) was high initially at 1Hz but then decreased sharply, which is consistent with the highest corrosion rates expected at elevated temperature and in the absence of corrosion inhibitor. Paris curve FCGR tests were subsequently conducted at 0.1Hz. Tests were performed in the worst case combinations of microstructure/environment/temperature identified from the frequency scan tests.

Finite Element Simulation of Stable Fatigue Crack Growth Using Critical CTOD Determined by Preliminary Finite Element Analysis

2014 ◽  
Vol 891-892 ◽  
pp. 1675-1680
Author(s):  
Seok Jae Chu ◽  
Cong Hao Liu
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Finite Element Simulation ◽  
Crack Growth ◽  
Crack Tip ◽  
Stress Intensity Factor Range ◽  
Crack Tip Opening Displacement ◽  
Element Analysis ◽  
Element Simulation

Finite element simulation of stable fatigue crack growth using critical crack tip opening displacement (CTOD) was done. In the preliminary finite element simulation without crack growth, the critical CTOD was determined by monitoring the ratio between the displacement increments at the nodes above the crack tip and behind the crack tip in the neighborhood of the crack tip. The critical CTOD was determined as the vertical displacement at the node on the crack surface just behind the crack tip at the maximum ratio. In the main finite element simulation with crack growth, the crack growth rate with respect to the effective stress intensity factor range considering crack closure yielded more consistent result. The exponents m in the Paris law were determined.

Modeling of Fatigue Crack Propagation

2004 ◽  
Vol 126 (1) ◽  
pp. 77-86 ◽  
Author(s):  
Yanyao Jiang ◽  
Miaolin Feng
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Fatigue Crack Propagation ◽  
Fatigue Crack Initiation ◽  
Cyclic Plasticity ◽  
R Ratio

Fatigue crack propagation was modeled by using the cyclic plasticity material properties and fatigue constants for crack initiation. The cyclic elastic-plastic stress-strain field near the crack tip was analyzed using the finite element method with the implementation of a robust cyclic plasticity theory. An incremental multiaxial fatigue criterion was employed to determine the fatigue damage. A straightforward method was developed to determine the fatigue crack growth rate. Crack propagation behavior of a material was obtained without any additional assumptions or fitting. Benchmark Mode I fatigue crack growth experiments were conducted using 1070 steel at room temperature. The approach developed was able to quantitatively capture all the important fatigue crack propagation behaviors including the overload and the R-ratio effects on crack propagation and threshold. The models provide a new perspective for the R-ratio effects. The results support the notion that the fatigue crack initiation and propagation behaviors are governed by the same fatigue damage mechanisms. Crack growth can be treated as a process of continuous crack nucleation.

Fatigue Crack Growth at Electrical Resistance Welding Seam of API 5L X-70 Steel Line Pipe at Varied Orientations

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Craig Taylor ◽  
Sreekanta Das ◽  
Laurie Collins ◽  
Muhammad Rashid
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Base Metal ◽  
Electrical Resistance ◽  
Weld Seam ◽  
Full Scale ◽  
Resistance Welding ◽  
Line Pipe ◽  
Full Scale Testing

Very few studies have been conducted concerning fatigue in steel line pipe and fewer using full-scale testing. Further, at the time of this study, no research on full-scale testing was available in open literature regarding fatigue behavior of line pipe with longitudinal cracks, despite being considered more critical than the line pipe with cracks oriented in the circumferential direction. In the current research work, fatigue crack growth was investigated in NPS 20, API 5L X-70 grade, electrical resistance welding (ERW) straight-seam steel line pipes in the base metal and at the weld seam for various orientations. It was found that there was no significant difference between fatigue crack growth in the base metal and at the weld seam for the tested stress ratio. Increasing the angle of inclination of the crack with respect to the weld line was found to decrease the rate of fatigue crack growth due to a decrease in the mode I stress component. Finally, it was observed that despite the difference in fatigue crack growth rates, the crack aspect ratios were nearly identical for all cracks at the same crack depth.

Transition Temperature Determination for Thick Wall Line Pipe

1998 ◽  
Author(s):  
G. Demofonti ◽  
G. Junker ◽  
V. Pistone ◽  
Gerd Junker ◽  
Valentino Pistone ◽  
...  
Keyword(s):  
Transition Temperature ◽  
Test Specimen ◽  
Laboratory Data ◽  
Full Scale ◽  
Thick Wall ◽  
Line Pipe ◽  
Brittle Transition ◽  
Brittle Transition Temperature ◽  
Ductile To Brittle Transition ◽  
Shear Area

The applicability of Drop Weight Tear Test specimen to evaluate the ductile to brittle transition temperature of thick wall pipes (30 mm and 40 mm wall thickness) has been investigated by comparing West Jefferson tests at different temperatures and laboratory data. The traditional API pressed notch specimen has been used with full and reduced thickness, together with chevron notch and weld notch starters. The different crack initiation methods have been examined with the goal of providing an easier test specimen, with reduced fracture energy. The 85% shear area transition temperature indicated by the different test specimen show a reasonable similarity, but the higher costs of preparation of the alternative notch geometries limit their adequacy in substituting the traditional pressed notch specimen. Good agreement has been found between standard DWTT specimen and full-scale test transition temperature. The results of this program together with literature data, confirm the validity of the DWTT specimen to measure the ductile to brittle transition temperature for thermomechanical rolled linepipe steels of thickness up to 40 mm. The reduced thickness specimens conservatively predicted full scale behaviour.

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