Purpose

This paper aims to make clear the sensitive zone of subsea pipeline to stress corrosion cracking (SCC) under a disbonded coating.

Design/methodology/approach

The change of microenvironment under a disbonded coating in artificial seawater was analyzed by using a rectangular crevice cell. The SCC behavior of subsea pipeline was studied by slow strain rate tensile tests.

Findings

The microenvironment at the crevice bottom exhibits obvious acidification, Cl- aggregation and cathodic protection potential (CP) rise. Accordingly, the susceptibility of X70 steels to SCC is high due to the intensive anodic dissolution effect. At the opening, hydrogen atom can access into the steel and induce hydrogen embrittlement effect on account of the applied over-protected CP potential, resulting in a relatively high susceptibility to SCC. The corrosiveness of the microenvironment at crevice middle, however, is mild with proper CP potential; thus, the susceptibility of X70 steel to SCC here is lower than that obtained at the opening and the crevice bottom.

Originality/value

A rectangular crevice cell is built to survey the microenvironment evolution under a disbonded coating in situ. The sensitive zone of subsea pipeline to SCC under a disbonded coating is clarified.

中文翻译：

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阴极保护下海水环境下剥离涂层缝隙中海底管道的微环境演变和SCC行为

目的

本文旨在弄清海底管道对剥离涂层下应力腐蚀开裂（SCC）的敏感区域。

设计/方法/方法

使用矩形缝隙池分析了人工海水中剥离涂层下的微环境变化。通过慢应变速率拉伸试验研究了海底管道的SCC行为。

发现

缝隙底部的微环境表现出明显的酸化，Cl-聚集和阴极保护电位（CP）升高。因此，由于强烈的阳极溶解作用，X70钢对SCC的敏感性很高。在开孔处，氢原子可进入钢中并由于施加的过保护的CP电位而引起氢脆效应，从而导致对SCC的敏感性较高。然而，缝隙中部的微环境腐蚀程度较轻，具有适当的阴极电位。因此，这里的X70钢对SCC的敏感性低于在开口和缝隙底部获得的敏感性。

创意/价值

建立一个矩形缝隙池，以观察原位剥离涂层下的微环境演变。明确了海底管道在剥离涂层下对SCC的敏感区域。