通过宏观检查、成分分析、力学性能、金相观察、扫描电镜等表征手段分析了海上某油田生产井不锈钢毛细管的失效原因。结果表明: 该直缝焊管失效段主要存在均匀外腐蚀和刀状腐蚀开裂的形貌。其中局部管段均匀外腐蚀后壁厚减少约30%; 而未腐蚀的完好管段按照GB/T 4334-2008进行了晶间腐蚀试验, 试验后其外观呈现出与现场样品形貌一致的焊缝热影响区沟槽, 这表明腐蚀失效的主要原因是不锈钢完好样品焊缝热影响区存在晶间腐蚀敏感性, 且腐蚀后沟槽在加压注入破乳剂时容易造成刀状腐蚀开裂。热影响区能谱观察结果从微观上证明了奥氏体晶界区存在铬偏析现象。依据失效分析结果提出了后续建议和改进措施。

The corrosion failure reasons of 316L stainless steel capillary for a producing well in an offshore oil field were investigated through macroscopic reasons, chemical composition analysis, mechanical property testing, metallographic analysis and scanning electrical microscopy. The results show that the corrosion morphology of failed sections of the straight seam welded capillary exhibited outer uniform corrosion and knife-line corrosion cracking. A section of the pipe showed outer uniform corrosion where the wall thickness was decreased by nearly 30% . After the corrosion test according to GB/T 4334-2008 with uncorroded intact samples, the appearance of the weld heat affected zone(HAZ) displayed the same surface groove profile as that of the field sample. This shows that the main reason of corrosion failure was the presence of intergranular corrosion susceptibility in the HAZ of the weld of the intact samples. The groove was easy to crack when the demulsifier was injected into the capillary in the pressurized conditions after corrosion. The EDS results obtained from the microscopic view from the HAZ demonstrates the presence of Cr segregation in the austenite grain boundary region. Some suggestions and improvement measures are put forward according to the results of failure analysis.