X65管线钢焊接接头在模拟浅表海水环境中的应力腐蚀试验研究

在海水环境中,由于海水从海底管道外管焊缝浸入,导致外管焊接接头断裂。为了研究可能导致X65外管焊接接头断裂的因素,应用慢应变速率拉伸试验(SSRT),通过应力-应变曲线、扫描电镜(SEM)等手段分析了3个X65管线钢焊接接头在空气及模拟浅表海水环境中的应力腐蚀性能。结果表明:在空气中X65钢焊接接头试样的延长量最大,达5.6 mm,在模拟海水中试样的延长量均减小,其中2号试样延长量最小,仅3.6 mm,表明试样在浅表海水中塑性变形能力降低;模拟海水中3个试样的应力腐蚀敏感性指数均处于有应力腐蚀倾向的范围;在空气中试样的断裂为韧性断裂;在浅表海水环境中试样的断裂为韧性断裂与脆性断裂的混合断裂,有应力腐蚀开裂的趋势;海水中含有的大量Cl~-导致焊接接头的应力腐蚀敏感性升高,失效风险增加。

Experimental Study of Stress Corrosion of X65 Pipeline Steel Welded Joint in Seawater Environment

In marine environment,seawater immersing from outer tube welds of submarine pipeline can lead to the fracture of welded joint of external pipe.To investigate the factors those may cause the fracture of welded joint of external pipe of X65 pipeline steel,stress corrosion cracking resistance of three X65 pipeline steel welded joints in air and simulated superficial marine environment was analyzed by the experimental methods of slow strain rate tension tests (SSRT),stress strain curve,and scanning electron microscopy (SEM).Results showed that the extended volume of welded joint of X65 steel in the air was the largest,which was 5.6 mm;while all the extended volumes in the simulated seawater decreased,the 2nd specimen had the least volume,which was only 3.6 mm,presenting that the plastic deformation capacity of specimens dropped in seawater.Moreover,all of the stress corrosion sensitivity indexes of specimens were in the range of trending toward stress corrosion.The fracture mechanism of specimen in air was ductile fracture,while that of specimens in marine environment was ductile fracture and brittle fracture,which had tendency to stress corrosion cracking.In general,the massive chloride ions in seawater resulted in the increase of stress corrosion cracking susceptibility and failure risk of welded joints.