We analyze the causes of the in-service loss of integrity of drill pipes made of G105 steel connected with their premature stress-corrosion fractures. In this case, the mechanical characteristics of steel are satisfactory, except a somewhat lowered elongation. At the same time, both in the structure and on the fracture surfaces of impact test specimens, we reveal a large number of corrosion-active nonmetallic inclusions of the calcium-aluminate type, which may increase the rate of local corrosion by an order of magnitude, promote the formation of deep pits on the inner surface of the pipe, and play the role of sites of initiation of corrosion-fatigue cracks. This is why we assume that the stage of crack initiation, which mainly determines the total durability of drill pipes after premature failures is controlled by the presence of corrosion-active nonmetallic inclusions and their density in the structure of steel.

中文翻译：

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非金属夹杂物在钻杆过早应力腐蚀断裂中的作用

我们分析了 G105 钢制成的钻杆在使用中的完整性丧失与其过早应力腐蚀断裂的原因。在这种情况下，钢的机械特性是令人满意的，只是伸长率有所降低。同时，在冲击试样的结构和断裂面上，我们发现了大量具有腐蚀活性的铝酸钙型非金属夹杂物，这可能使局部腐蚀速率提高一个数量级。 ，促进管道内表面深坑的形成，起到腐蚀疲劳裂纹萌生部位的作用。这就是为什么我们假设裂纹萌生阶段，