影响管线钢应力腐蚀破裂的力学和材料因素.pdf

? ? ?1 ,2,? 1 ,? ?2 (1. 上海交通大学材料科学与工程学院,上海200030 ;2.上海材料研究所,上海200437) ?:介绍了有关管线钢应力腐蚀破裂(SCC)的类型及特点,重点阐述了影响管线钢SCC的 力学和材料因素。在力学方面,分析了管线的最大运行应力、 压力波动R值(最小和最大压力的比 值)、 残余应力以及应变速率对SCC的重要影响。在材料方面,介绍了不同钢级管线钢的化学成分 和显微组织,并对不同SCC形式下,材料的化学成分、 显微组织对SCC行为的影响进行了讨论。 ?:管线钢;应力腐蚀破裂;应力;应变速率;材料;化学成分;显微组织 ?: TG142. 41 ; TG172. 8 ?: A ?: 100023738(2002)0420001205 The Factors of Mechanics and Materials Influencing Stress Corrosion Cracking of Pipeline Steels GUO H ao1 ,2, CAI Xun1, YANG Wu2 (1. Shanghai Jiaotong University , Shanghai 200030 ;2. Shanghai Research Institute of Materials , Shanghai 200437 , China) Abstract :The types and characteristics of stress corrosion cracking(SCC) of pipeline steels are introduced. The factors of mechanics and materials influencing SCC of pipeline steels are discussed. Regarding mechanics , the important effects of maximun operational stress ,R(ratio of minimum to maximumpressure) , residual stress and strain rate on SCC are analyzed. As to materials , the chemical compositions and microstructures of different pipeline steels are introduced , and their roles in SCC behavior are also discussed. Key words :pipeline steel ; stress corrosion cracking; stress; strain rate; material ; chemical composition; mi2 crostructure 1? 腐蚀往往给油气田造成重大经济损失、 灾难性 事故和环境污染。如若采取适当的防护措施,腐蚀 造成的经济损失的30 %40 %可以挽回,加强腐蚀 与防护研究可为石油工业带来巨大的经济效益。 应力腐蚀破裂(SCC)为环境致裂的一种形式, 局部环境、 材料的电位、 外加应力、 保护涂层状况、 运 行温度以及材料的热处理等在这种失效中起了重要 作用。1965年美国Louisiana州发生了第一起地下 气体管线土壤侧(外部) SCC事故,环境为浓CO2 - 3/ HCO - 3,pH 9. 5 ,为沿晶SCC( IGSCC)。 此后,美 ?:2001212231 ;?:2002203201 ?:国家重点基础研究专项经费资助项目(G19990650) ?:郭 浩(1971 - ) ,男,山东青岛人,上海交通大学博士 生(上海材料研究所合作培养)。 ?:蔡 教授,杨武研究员。 国、 澳大利亚、 加拿大、 巴基斯坦、 前苏联以及伊朗都 有相关的事故报道,失效的最短时间分别为7年(美 国)和6年(伊朗)。1985年加拿大发生的管线 SCC ,pH B F + P。对F + P钢,当R较高 时,SCC敏感性增加;而对B F显微组织,当R较低 时,SCC敏感性增加。Jeffrey19对近中性环境中 X70钢的显微组织对SCC的影响进行了研究,结果 表明,显微组织和杂质对SCC和腐蚀行为都有影 响。淬火组织有最大腐蚀速率和最高SCC敏感性, 退火组织有最好的耐蚀性和耐SCC特性。他们同 时指出,粗大晶粒的退火组织比细小晶粒的正火组 织更抗SCC ,并且如果腐蚀速率减小,SCC敏感性 降低,这与Beavers提出的粗大晶粒的热影响区 (HAZ)对近中性pH SCC更敏感的结论相矛盾。大 部分研究者认为高pH环境SCC对显微组织敏感。 Asahi20的研究表明,不同组织对IGSCC敏感性不 同,均匀组织能提高钢的抗SCC性能,B比F + P更 抗SCC。这与Kushida有关近中性pH环境中显微 组织对SCC的影响的观点是一致的。 (3)冷加工的影响 冷加工和局部应变是SCC 的加速因素。由于冷加工能提高钢的强度,降低韧 性,并且在溶液中能促进金属中氢浓度的增加,所以 促进钢的SCC。氢一旦以原子形式被吸收进金属 后,将倾向于扩散,并且在位错处钉扎。冷加工不仅 增加陷阱浓度,极大增加氢的溶解性;同时,它也能 影响阳极溶解型的SCC。冷加工的金属比退火态 金属能产生更多的阳极溶解活性点,而且冷加工材 料表面形成的钝化膜有较弱的保护性,这可能导致 局部腐蚀的较早萌生,并且在应力或应变存在的情 况下,导致钢的SCC。 4? (1)管线钢SCC的发生存在一个阈值应力(或 阈值应力强度 ) , 只有应力超过它SCC才能发生。 (2)应力波动是裂纹萌生和扩展的必要条件。 (3)应变和应变速率比实际应力更重要,应变 速率是SCC扩展的控制参数,如果应变速率低于其 临界值,裂纹将停止扩展。 (4)今后的研究工作中应综合考虑应力水平、 应力波动以及应变速率对SCC的共同作用,同时考 虑管线总的应力,从而获得更加合理的裂纹萌生、 扩 展表达式. (5)材料方面,由于目前管线钢不同的化学成 分和显微组织对高pH SCC和近中性pH SCC的影 响尚无定论,尤其是近中性pH环境的SCC研究时 间较短,所以需要更加广泛而细致的研究工作。 ?: 1 Kentish P J. Gas pipeline failures: Australian expericenceJ . Br Corros J , 1985 , 20(3) : 139146 . 2 Burke Delanty , et al. Major field study compares pipeline SCC with coatingsJ . Oil & Gas Journal , 1992 , June 15 : 3944. 3 John A Beavers , et al. Materials factors influencing the initiation of near - neutral pH SCC on underground pipelinesR. 2000 In2 ternational Pipeline Conference - Volume 2 , ASME 2000 : 979 988. 4 Gu B , et al.Transgranular stress corrosion cracking of X - 80 and X- 52 pipeline steels in dilute aqueous solution with near - neutral pHJ . Corrosion ,1999 , 55(3) : 312319. 5 Carl E Jaske , et al. 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