深水及阴极保护下双相不锈钢氢致应力开裂的氢行为与临界电位研究

In recent years, failure cases attributed to Hydrogen Induced Stress Cracking (HISC) of Duplex Stainless Steels (DSS) using as deepwater subsea facilities under Cathodic Protection (CP) has been reported, which increases the safety risk of materials and structures during deep sea exploitation. Using and design of DSS under CP in deep sea safely and reasonably become a new challenge to researcher. This project will focus on the HISC of DSS, and arrange research content about the kinetics of hydrogen gas evolution, hydrogen atoms absorption on the metal surface and hydrogen atoms adsorption and uptake by metal under the combined environment of deep water subsea and cathodic protection potential. High pressure autoclaves for simulating of subsea pressure, high pressure slow strain rate tensile test (SSRT), high pressure electrochemical measurement and hydrogen permeation test using high pressure electrode probes will be utilized to investigate the environmental effects of high hydraulic pressure, low temperature, water flow and other physical or chemical factors in deep water subsea and the electrochemical effects of the cathodic polarization induced by CP system. Based on the research on the rule and influencing factors of hydrogen gas evolution under high pressure and flow condition, hydrogen atoms absorption status on the DSS surface influenced by cathodic polarization and calcareous deposit, hydrogen atoms uptake from absorption to adsorption and the hydrogen permeation from surface to bulk of DSS, the mechanism of hydrogen kinetics under cathodic potential can be drawn and the critical potential range and critical hydrogen concentration for HISC can be confirmed. All the results can be used as the theoretical basis for failure control of DSS and the guide of CP design for DSS using in deep water.

近几年国际上陆续出现深海环境中双相不锈钢在阴极保护下的氢致应力开裂失效案例，给深水开发过程中的材料和结构安全带来极大风险，也给双相不锈钢在阴极保护下的合理使用提出新的挑战。本课题针对诱发这一氢致应力开裂失效的深水环境及阴极极化条件下的氢析出、吸附和进入金属的动力学机制开展研究，利用高压腐蚀环境模拟、高压电化学测试及氢渗透测试、高压慢应变拉伸等试验方法，研究深水高水压、低温、流动等物理及化学环境和阴极保护电化学环境的共同作用下，双相不锈钢阴极析氢过程中氢气析出、氢原子吸附于表面及氢原子吸收进入金属的动力学过程及影响因素，揭示阴极电位与氢致应力开裂临界氢浓度的相关性及其对氢行为影响机制。确定深水环境下导致双相不锈钢氢致应力开裂的临界阴极保护电位区间，为建立深水环境下双相不锈钢失效控制和阴极保护设计规范提供理论支撑。

由于深海环境的苛刻性和高风险性，材料安全性和可靠性要求显著提高。双相不锈钢作为目前深水设施的首选材料，在海水中与高强钢构件联合阴极保护容易导致氢原子进入金属造成氢致应力开裂。近年陆续出现深海环境中双相不锈钢的氢致应力开裂失效案例，给深水开发过程中的材料和结构安全带来极大挑战。.本课题针对诱发这一氢致应力开裂失效的深水环境及阴极极化条件下的氢析出、吸附和进入金属的动力学机制开展研究，利用高压腐蚀环境模拟、高压电化学测试、氢渗透测试、恒应变和慢应变拉伸测试等试验方法，研究深水高水压、低温、钙镁沉积等物理及化学环境和阴极保护电化学环境的共同作用下，双相不锈钢及高强管线钢阴极析氢过程中氢气析出、氢原子吸附及氢原子吸收进入金属的动力学过程及影响因素，揭示阴极电位与氢致应力开裂临界氢浓度的相关性，确定深水环境下导致双相不锈钢氢致应力开裂的临界阴极保护电位区间。.研究表明，在深水低温、高静水压及外加载荷条件下，氢原子复合成氢分子和氢气泡析出受到抑制，增加吸附在不锈钢表面的氢原子浓度，促进氢进入金属内部。深水环境下钙镁沉积层在金属表面的生成也利于氢渗透过程的进行和吸附氢浓度的增加。阴极电流密度增加，稳态氢渗透电流密度越大，进一步增大表面吸附氢浓度。基于表面状态、施加载荷和阴极极化等条件对于金属亚表面氢浓度的影响，建立了阴极极化条件下吸附氢原子进入金属的动力学模型。通过双相不锈钢在模拟深水工况下的恒应变和慢应变拉伸实验等工作，明确了阴极极化电位负移诱发不锈钢脆性断裂的规律与机制，确定了双相不锈钢氢致应力开裂的敏感电位区间为-950~-1050mVSCE以及氢含量达到10~15ppm为影响其开裂的敏感值。.研究成果不仅通过多篇论文发表，为建立深水环境下双相不锈钢失效控制和阴极保护设计规范提供理论支撑，同时为我国首个深水气田开发水下油气设施选材设计提供了重要的理论先导和数据支撑。