Fundamental studies of environmentally assisted surface cracking in pipeline steels

管线钢环境辅助表面裂纹的基础研究

• 批准号: RGPIN-2019-04945
• 负责人: Chen, Weixing
• 金额: $ 3.35万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=746861
• 关键词: Fundamental; studies; environmentally; assisted; surface

There exist many dilemmas in the research community when it comes to dealing with environmentally assisted cracking, a major cause of failures of many facilities and components, in Canada and worldwide. Investigations to understand failure mechanisms have been conducted, either using smooth bar specimens with aggressive mechanical loading, such as slow strain rate testing, or using compact tension specimens, representing the growth behavior of long and through-thickness cracks, which are very different from the cracks formed in susceptible structures during field service. In the latter case, surface cracks or thumbnail-shaped flaws are initiated and grown. Before the surface cracks are growing into a through-thickness crack, some structures, for example, steel pipelines for oil and gas transmission, may have already lost their serviceability. Therefore, it is very desirable to study the fundamental behavior of surface cracks. From a fundamental analysis of cracks developed from field service, it has been identified that 1) the environmentally assisted surface cracks in pipeline steels started with preferential growth along their surface length direction by initiating new small cracks in the vicinity of but independent from an existing crack, rather than by extending the length of the existing crack through a direct growth at their crack tips; 2) the crack depth often remains dormant because its growth is not environmentally favorable, 3) however, the growth in length direction increases the mechanical driving forces at the depth tip even though the depth tip remains dormant geometrically. This research is targeted to provide a fundamental understanding of the growth of surface cracks along their length direction, especially by initiating small cracks in the vicinity of but independent from existing cracks. It has been analyzed that the growth of surface cracks in their length direction preferentially through constant small crack initiations is affected strongly by the yielding behavior of pipeline steels and/or their microstructures, depending on the type of corrosion environments and variable pressure fluctuations encountered during service. All these factors are mutually related to each other in terms of their effect on surface crack growth. This proposal will address the above factors individually and synergistically to provide a fundamental understanding of the problem. It is expected that the findings will be critical in the development of new materials with improved resistance to environmentally assisted cracking and in the formulation of better operating strategies for pipeline steels, achieving higher operation integrity and pipeline safety.

在处理环境辅助裂纹时，研究界存在许多困境，环境辅助裂纹是加拿大和世界各地许多设施和部件故障的主要原因。已经进行了了解失效机制的研究，要么使用具有剧烈机械载荷的光滑棒样本，例如慢应变率测试，要么使用紧凑的拉伸样本，代表长裂纹和全厚度裂纹的生长行为，这与传统的裂纹扩展行为有很大不同。现场使用期间易受影响的结构中形成的裂缝。在后一种情况下，表面裂纹或缩略图形缺陷开始并生长。在表面裂纹发展为全厚度裂纹之前，一些结构，例如用于石油和天然气输送的钢质管道，可能已经丧失了使用能力。因此，研究表面裂纹的基本行为是非常有必要的。 通过对现场使用中产生的裂纹进行基本分析，可以确定：1) 管线钢中的环境辅助表面裂纹是通过在现有裂纹附近但独立于现有裂纹产生新的小裂纹，沿着其表面长度方向优先生长的。 ，而不是通过在裂纹尖端直接生长来延长现有裂纹的长度； 2) 裂纹深度通常保持休眠状态，因为其生长对环境不利，3) 然而，长度方向的生长增加了深度尖端处的机械驱动力，即使深度尖端在几何上保持休眠状态。这项研究的目的是提供对表面裂纹沿其长度方向生长的基本了解，特别是通过在现有裂纹附近但独立于现有裂纹产生小裂纹。据分析，表面裂纹在其长度方向上的生长优先通过恒定的小裂纹萌生，受到管线钢和/或其微观结构的屈服行为的强烈影响，具体取决于腐蚀环境的类型和使用期间遇到的可变压力波动。所有这些因素对表面裂纹扩展的影响都是相互关联的。该提案将单独和协同地解决上述因素，以提供对问题的基本理解。预计这些发现对于开发具有更高抗环境辅助开裂能力的新材料以及制定更好的管线钢操作策略、实现更高的操作完整性和管道安全性至关重要。