Room Temperature Creep Behaviour of Pipeline Steels and Its Influence on Stress Corrosion Cracking

Author(s):  
Weixing Chen ◽  
Sheng-Hui Wang

Room temperature creep is often of significant importance in structural materials. Its occurrence, for example, may be an important factor contributing to crack growth during stress corrosion cracking. For pipeline steels used in gas transmission, room temperature creep deformation near the crack tip may result in a time dependent crack growth. In this research, room temperature creep of two pipeline steels with different grades was studied under various loading conditions including pure static, pure cyclic and a combination of static and cyclic loading. The creep deformation under a stress higher than the yield strength may represent the deformation behaviour at the crack tip. Due to cyclic hardening, all the steels crept at a stress higher than the yield strength exhibit cyclic creep retardation, which is less pronounced at lower stress-ratio (minimum stress/maximum stress). Pre-cyclic loading has significant effect on subsequent static creep. In general, pre-cyclic loading causes a burst of creep deformation under subsequent static loading, which may result in significantly larger cumulative creep strain than that of pure static creep depending on the initial loading strain and the number of cycles in pre-cyclic loading. The burst in creep deformation requires an incubation period that increases with number of prior load cycles. The burst strain is dependent on the number of cycles of prior cyclic loading in a more complicated manner. The implication of the creep behaviour observed in these tests is also discussed in terms of stress corrosion cracking in the pipeline steels.

Author(s):  
Scott X. Mao ◽  
J. L. Luo ◽  
B. Gu ◽  
W. Yu

The stress corrosion cracking (SCC) of pipeline steels in coating disbondment chemistry (near neutral pH solution) was studied by using slow strain rate tests (SSRT), polarization techniques, SEM and SIMS (secondary ion mass spectroscope). It was found that SCC susceptibility increased as the applied electrochemical potential and strain rates decreased. Hydrogen (H) precharging or addition of CO2 facilitated the process of SCC, suggesting that dissolution and hydrogen ingress are involved in the cracking process. SIMS analysis showed that hydrogen could diffuse into steels around the crack tip during the SCC process, which would facilitate the dissolution rate of the steel and increase SCC susceptibility. A mechanism was proposed which shows that hydrogen enhances anodic dissolution type of SCC in dilute aqueous solution. A thermodynamic analysis of the SCC process was carried out, and was found to be consistent with the experimental results.


Materials ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1683 ◽  
Author(s):  
Yi Ma ◽  
Xianwei Huang ◽  
Yuxuan Song ◽  
Wei Hang ◽  
Taihua Zhang

The crystal orientation effect on mechanical heterogeneity of LiTaO3 single crystals is well known, whilst the time-dependent plastic behavior, i.e., creep is still short of understanding. Relying on nanoindentation technology, we systematically studied room-temperature creep flows at various holding depths (100 nm to 1100 nm) in three typical orientations namely the X-112°, Y-36° and Y-42° planes. Creep resistance was much stronger in the X-112° plane than the others. In the meanwhile, creep features were similar in the Y-36° and Y-42° planes. The orientation effect on creep deformation was consistent with that on hardness. The nanoindentation length scale played an important role in creep deformation that creep strains were gradually decreased with the holding depth in all the planes. Based on strain rate sensitivity and yield stress, the activation volumes of dislocation nucleation were computed at various nanoindentation depths. The activation volumes ranged from 5 Å3 to 23 Å3 for the Y-36° and Y-42° planes, indicating that a point-like defect could be the source of plastic initiation. In the X-112° plane, the activation volume was between 6 Å3 and 83 Å3. Cooperative migration of several atoms could also be the mechanism of dislocation activation at deep nanoindentation.


2014 ◽  
pp. 1221-1226 ◽  
Author(s):  
Pierre-Olivier St-Arnaud ◽  
Donald Picard ◽  
Houshang Alamdari ◽  
Donald Ziegler ◽  
Mario Fafard

2006 ◽  
Vol 41 (6) ◽  
pp. 1797-1803 ◽  
Author(s):  
Bingyan Fang ◽  
En-Hou Han ◽  
Jianqiu Wang ◽  
Ziyong Zhu ◽  
We Ke

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