The Effect of Microstructure on Pit-to-Crack Transition and Crack Growth in an X-52 Pipeline Steel in Near-Neutral pH Environment

2008 ◽  
Author(s):  
B. Fang ◽  
R. Eadie ◽  
W. Chen ◽  
M. Elboujdaini ◽  
E.-H. Han
Keyword(s):  
Normal Stress ◽  
Pipeline Steel ◽  
Crack Depth ◽  
Width Ratio ◽  
Blunt Crack ◽  
Neutral Ph ◽  
Metallic Inclusions ◽  
Corrosion Pits ◽  
Crack Transition ◽  
Pit Depth

X-52 pipeline steel specimens that had been pitted using a passivation/immersion technique were cyclically loaded in a near-neutral pH solution sparged with 5% CO2/balance N2 gas mixture at a peak normal stress of 109% of the yield strength (YS), a stress ratio, R, of 0.8, and a frequency of 0.0001 Hz. Blunt cracks were seen to have initiated from the corrosion pits. There were many more cracks on the radial transverse (R-T) surface than on the axial transverse (A-T) surface. On the R-T surface, there were a lot of non-metallic inclusions particularly at mid-wall in this steel and these resulted in the nucleation of large pits that were particularly prone to pit-to-blunt-crack transition. At higher peak normal stress, 109% of YS, compared to previous studies at a little lower stresses, there was more rapid crack formation on the R-T surface. In the end, the cracks along the large elongated inclusions penetrated into the steel samples and led to failure. The crack path was transgranular in nature and the fracture surface displayed quasi-cleavage features. Analysis revealed that the pit depth to width ratio for individual pits was a little higher than that for linked pits, however, the ratio of crack depth to crack mouth width was observed to be much larger than the ratio for the linked pits. Strong preferential dissolution was believed to be responsible for the pit nucleation from these non-metallic inclusions, with the plastically deformed regions at the pits acting as the anodic phases.

Numerical Study of the Crack-Front Constraint for SENT Specimens of X80 Pipeline Steel

2017 ◽  
Vol 898 ◽  
pp. 735-740
Author(s):  
Ting Zhong ◽  
Lin Zhu ◽  
Yan Zhou ◽  
Jian Shuai ◽  
Lan He
Keyword(s):  
Crack Front ◽  
Numerical Study ◽  
Pipeline Steel ◽  
Crack Depth ◽  
Stress Triaxiality ◽  
Width Ratio ◽  
Specimen Thickness ◽  
X80 Pipeline Steel ◽  
Specimen Width ◽  
Average Measure

This work presents a numerical study of crack-front constraint for SENT specimens of X80 pipeline steel, to examine geometry effect on the correlation of crack-front stress field and constraint. An average measure of constraint over crack-front Am was employed to characterize the crack-front constraint. SENT specimens with varying geometries (different crack depth to specimen width ratio, a/W, and different specimen width and thickness, W/B) were analyzed by Gurson-Tvergaard-Needleman model (GTN model). Results showed that the stress triaxiality Am can characterize the crack-front constraint of X80 pipeline steel very well. The level of the Am-△a curve rises with the decrease of crack depth, and increases first and then decreases with the increase of SENT specimen thickness.

Blunt Crack Initiation and its Transition to Sharp Cracks in Pipeline Steel in Near-Neutral pH Solution

2012 ◽  
Author(s):  
B. Fang ◽  
R. L. Eadie ◽  
M. Elboujdaini
Keyword(s):  
Crack Growth ◽  
Pipeline Steel ◽  
High Stress ◽  
Crack Tip ◽  
Crack Mouth ◽  
Blunt Crack ◽  
Neutral Ph ◽  
Aspect Ratios ◽  
Risk Of Failure ◽  
Mouth Width

This paper reviews our research into pipeline stress corrosion cracking (SCC) in near-neutral pH (NNpH) environment to help understand the mechanisms on pit-to-crack transition and early growth to contribute to pipeline integrity management so that the risk of failure can be avoid or reduced. Pitted specimens by using two different techniques (passivation/immersion and electrochemical methods) were cyclically loaded in NNpH environment sparged with 5% CO2 / balance N2 gas mixture at high stress ratios (minimum stress/maximum stress), low strain rates and low frequencies which are close to the operational pipelines in the field. Blunt cracks initiation was seen first and associated with the pit geometry, and most of the blunt cracks were observed to have initiated from the corrosion pits that had the pit depth to surface width aspect ratios greater than 0.5. The blunt crack growth was engendered by anodic dissolution, which was facilitated by stress. So it was called as stress facilitated dissolution crack growth. These blunt cracks had considerably large crack tip width to crack mouth width aspect ratios, and the majority were below 0.5 to 0.6 mm deep, and considered dormant. Once cracks surpassed the critical value, around 0.5 to 0.6 mm, the cracks would be reactivated and the crack tip width to crack mouth width ratios became significantly smaller. Meanwhile, more hydrogen would be trapped in the plastic zones. Thus, hydrogen would play an important role in the crack propagation. So in this stage, cracks tended to become sharp and the mechanism was referred to hydrogen facilitated cracking. The observations from the field can be interpreted very well by using the proposed models. It was proposed that two different mechanisms are responsible for the early-stage crack growth and sharp cracks be removed to reduce the risk of failure in pipelines.

scholarly journals Reflections on Early Stages of Environmentally Assisted Cracking from Corrosion Pits

2021 ◽  
Vol 2 (4) ◽  
pp. 568-581
Author(s):  
Alan Turnbull
Keyword(s):  
Crack Growth ◽  
Grinding Wheel ◽  
Specimen Preparation ◽  
Environmentally Assisted Cracking ◽  
Variable Nature ◽  
Aqueous Chloride ◽  
Fabrication Defects ◽  
Corrosion Pits ◽  
Crack Transition ◽  
Pit Depth

A perspective is presented on the evolution of damage due to environmentally assisted cracking (EAC), from crack precursor development through to long crack growth. The variable nature of crack precursors is highlighted with an observation that uncontrolled chemistry excursions or fabrication defects could eliminate any significant delay associated with that step in the damage evolution process. Specimen preparation by machining and grinding can be critical in determining the apparent susceptibility of the metal to EAC and corrosion, and an example for 316L stainless steel is given to show how physical defects generated by the grinding wheel can become the dominant site for pitting attack relative to MnS inclusions. Corrosion pits are the most commonly observed precursor to cracks in aqueous chloride environments. The loci of sites of crack initiation around a pit are discussed and the inherent challenges in quantifying the growth of cracks smaller than the pit depth described with implications for modelling of the pit-to-crack transition. The remarkably enhanced stress corrosion crack growth rate data for short and small cracks in a 12Cr steam turbine blade in a simulated condensate environment are discussed in the context of crack electrochemistry modelling and the implications for engineering integrity.

Application of Constraint Corrected J-R Curves to Fracture Analysis of Pipelines

2005 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Brian N. Leis
Keyword(s):  
Finite Element ◽  
Test Data ◽  
Pipeline Steel ◽  
Crack Depth ◽  
Crack Tip ◽  
Mathematical Expression ◽  
Width Ratio ◽  
Single Edge ◽  
X80 Pipeline Steel ◽  
Element Analysis

Fracture properties of API X80 pipeline steel have been developed using a set of single edge notched bend (SENB) and single edge notched tension (SENT) specimens with shallow and deep cracks to generate different crack-tip constraint levels. The test data show that the J-R curves for X80 pipeline steel are strongly constraint dependent. To facilitate transfer of the experimental J-R curves to those for actual cracked components, like flawed pipeline, constraint corrected J-R curves are developed. The two-parameter J-A2 formulation is adopted to quantify constraint effect on the crack-tip fields and the J-R curves. The constraint parameter A2 is extracted by matching the J-A2 solution with finite element results for a specific crack configuration. A constraint corrected J-R curve is then formulated as a function of the constraint parameter A2 and crack extension Δa. A general method and procedure to transfer the experimental J-R curves from laboratory to actual cracked components are proposed. Using the test data of J-R curves for the SENB specimens, a mathematical expression representing a family of the J-R curves is constructed for X80. It is shown that the predicted J-R curves developed in this paper match well with experimental data for both SENB and SENT specimens. To demonstrate its application in assessing flaw instability, a pipeline with an axial surface crack is considered. For a crack depth of 50% of the wall thickness, the predicted J-R curve is found to be higher than that for the SENB specimen with the same crack length to width ratio. From this predicted J-R curve and crack driving force obtained by finite element analysis, the failure pressures of the pipeline at the crack initiation and instability are determined and discussed.

Application of Constraint Corrected J-R Curves to Fracture Analysis of Pipelines

2005 ◽  
Vol 128 (4) ◽  
pp. 581-589 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Brian N. Leis
Keyword(s):  
Finite Element ◽  
Test Data ◽  
Pipeline Steel ◽  
Crack Depth ◽  
Crack Tip ◽  
Mathematical Expression ◽  
Width Ratio ◽  
Single Edge ◽  
X80 Pipeline Steel ◽  
Element Analysis

Fracture properties of an API X80 pipeline steel have been developed using a set of single edge notched bend (SENB) and single edge notched tension (SENT) specimens with shallow and deep cracks to generate different crack-tip constraint levels. The test data show that the J-R curves for the X80 pipeline steel are strongly constraint dependent. To facilitate transfer of the experimental J-R curves to those for actual cracked components, like flawed pipeline, constraint corrected J-R curves are developed. The two-parameter J-A2 formulation is adopted to quantify constraint effect on the crack-tip fields and the J-R curves. The constraint parameter A2 is extracted by matching the J-A2 solution with finite element results for a specific crack configuration. A constraint corrected J-R curve is then formulated as a function of the constraint parameter A2 and crack extension Δa. A general method and procedure to transfer the experimentalJ-R curves from laboratory to actual cracked components are proposed. Using the test data of J-R curves for the SENB specimens, a mathematical expression representing a family of the J-R curves is constructed for the X80. It is shown that the predicted J-R curves developed in this paper agree well with experimental data for both SENB and SENT specimens. To demonstrate its application in assessing flaw instability, a pipeline with an axial surface crack is considered. For a crack depth of 50% of the wall thickness, the predicted J-R curve is found to be higher than that for the SENB specimen with the same crack length to width ratio. From this predicted J-R curve and crack driving force obtained by finite element analysis, the failure pressures of the pipeline at the crack initiation and instability are determined and discussed.

scholarly journals Influence of the ultrasonic surface rolling process on stress corrosion cracking susceptibility of high strength pipeline steel in neutral pH environment

RSC Advances ◽  
2017 ◽  
Vol 7 (59) ◽  
pp. 36876-36885 ◽  
Author(s):  
Bingying Wang ◽  
Yu Yin ◽  
Zhiwei Gao ◽  
Zhenbo Hou ◽  
Wenchun Jiang
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Pipeline Steel ◽  
High Strength ◽  
Rolling Process ◽  
Corrosion Cracking ◽  
X80 Pipeline Steel ◽  
Enhancement Technique ◽  
Neutral Ph ◽  
Developed Surface

A developed surface enhancement technique, USRP, was applied on X80 pipeline steel and the stress corrosion cracking susceptibility was studied.

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