以X-70管线钢近中性pH值溶液(NS4和实际土壤溶液)为研究对象, 研究了恒载荷、慢应变速率拉伸(SSRT)和循环载荷等不同条件下的环境开裂行为.结果表明, 在该体系中局部应变速率是联系各种不同断裂过程的纽带, 决定着断裂的模式.当该局部应变速率低于发生应力腐蚀开裂(SCC)敏感局部应变速率的上限(即5×10-5 s-1)时,SCC才能够发生；在循环载荷作用下, 当该局部应变速率高于此上限时, 将发生力学因素起主导作用的腐蚀疲劳(CF)开裂；该局部应变速率继续升高时, 将发生机械断裂. 对X-70管线钢在近中性pH值的环境开裂, 不论开裂过程是溶解或(和)氢的作用占主导, 均受局部应变速率控制. 在通常遇到的现场服役条件下, X-70管线钢在近中性pH值溶液中的开裂模式是SCC, 不是CF, 应称之为“近中性pH 值应变促进腐蚀开裂”, 实质上这是一种由局部应变速率决定的环境开裂行为.
Environmentally assisted cracking (EAC) of X-70 pipeline steels in near-neutral pH environments, including the standard solution, NS4, and an actual soil solution, was investigated using constant loading tests, slow strain rate tests (SSRT) and cyclic loading tests. It was revealed that local strain rate is a key factor that builds a bridge between different tests, different samples and different cracking processes, and dominates fracture mode. Therefore, local strain rate is one of the most important parameters in the EAC of X-70 pipeline steels. Stress corrosion cracking (SCC) can occur only if the local strain rate is smaller than the upper susceptible local strain rate for SCC, i.e. 5×10-5 s-1. As for cyclic loading tests, when the local strain rate is higher than this upper local strain rate for SCC, corrosion fatigue (CF) will occur. Further more, mechanical facture will take place if the local strain rate is high enough. Meanwhile, it is shown that as far as the EAC of X-70 pipeline steels in near-neutral pH environments is concerned, the cracking is dominated by the local strain rate no matter which the mechanism is, dissolution or (and) hydrogen related process. Thus the mechanism of the near-neutral pH cracking for X-70 in-service pipelines in the field is SCC instead of CF. In addition, it is proposed that the term of near-neutral pH SCC is inappropriate, which should be replaced by near-neutral strain assisted corrosion cracking to better describe the EAC of X-70 pipeline steels that is, in fact, local-strain-rate-based environmentally cracking.
参考文献
| [1] | |
| [2] | |
| [3] | |
| [4] | |
| [5] | |
| [6] | |
| [7] | |
| [8] | |
| [9] | |
| [10] | |
| [11] | |
| [12] | |
| [13] | |
| [14] |
- 下载量()
- 访问量()
- 您的评分：
-
10%
-
20%
-
30%
-
40%
-
50%