井下含硫環空液中P110油管鋼應力腐蝕開裂的電化學噪聲特征

井下含硫環空液中P110油管鋼應力腐蝕開裂的電化學噪聲特征Electrochemical noise of stress corrosion cracking of P110 tubing steel in Sulphur -containing downhole annular fluid

采用慢應變速率拉伸試驗(SSRT)，并結合電化學噪聲(ECN)、掃描電鏡(SEM)與電化學阻抗(EIS)等方法，研究了P110低合金油管鋼在模擬井下環空溶液中的應力腐蝕開裂(SCC)行為，并探討了S2-離子濃度對裂紋萌生和擴展過程的影響。結果表明：在P110鋼的彈性形變階段，環空溶液中低濃度S2-離子的加入加速了P110鋼拉伸試樣表面鈍化膜的破壞，導致ECN曲線上出現許多由亞穩態點蝕引起的短時電流噪聲峰。S2-離子的加入還顯著縮短了亞穩態點蝕向穩定點蝕轉變的時間，促使拉伸試樣表面出現較大尺寸的蝕坑，這些蝕坑在拉應力作用下可以轉變為裂紋萌生源。相比亞穩態點蝕，裂紋生長產生的噪聲峰平均壽命更長(~400s)，且噪聲幅值(~40μA)和積分電量(~4000μC)也更大。P110鋼的SCC以陽極溶解為主，且裂紋生長速率隨S2-濃度的增加而增大，但裂紋生長則是斷續而非連續進行的。

The stress corrosion cracking (SCC) behavior of P110 low alloy steel in simulating sulphur-containing annular fluid（SAF）and the effect of S2- concentration on the initiation and propagation of crack are investigated by slow stress rate test (SSRT), electrochemical noise (EN), scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS) techniques. The results show that, during the elastic stress stage, the addition of S2- accelerates the breakdown of passivation film on the surface of P110 steel tensile specimen. There are many short duration current transients caused by metastable pits on ECN curves. The transformation time of metastable to stable pits is shortened significantly by the addition of S2- ions, which not only promotes the growth of pits but the initiation of cracks from the stable pits under the action of tensile stress. Compared with the ECN spikes from metastable pits, the spikes associated to the advance of cracks are featured by longer average duration (~400s), stronger amplitude (40 μA), and higher charge (~4000 μC). The susceptibility of P110 steel to SCC increases with S2- concentration, and the propagation of SCC is dominated by anodic dissolution characteristic of discontinuous advance.

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