Unraveling the local stress corrosion cracking behavior of Alloy 690 plug in a high-temperature concentrated alkaline solution

Abstract

The stress corrosion cracking (SCC) performance of the sealed Alloy 690 plugs was investigated in 350 °C deoxygenated concentrated alkaline solution. Sealing was used to expose only the inner surface of the plug, preventing direct contact between the tube sheet and the concentrated alkaline solution. After exposure for 1000 h, several intergranular cracks were observed on the inner wall of the plugs. Stress corrosion cracks primarily appear in some regions on the inner wall, which are highly deformed and advanced along the random grain boundary. The internal oxide layer formed in the high-temperature alkaline solution was not dense; it comprised a composite oxide with multiple layers. The outermost layer consisted of Fe-Cr-Ni oxide particles, and beneath it was an uneven Ni-rich layer, followed by a thin Cr-rich layer closest to the matrix. High kernel average misorientation in the heavily deformed region and a lack of chromium carbide contributed to crack initiation and propagation of Alloy 690 plug in hot concentrated alkaline solutions.