Effect of iron content on corrosion resistance of Ni-Cr-Mo alloy weld overlays in H_2S containing environments

摘要

Corrosion tests were carried out to determine the effect of iron content on localised corrosion and stress corrosion cracking (SCC) resistance of Ni-Cr-Mo alloy weld overlays (i.e. Alloy 625) in H_2S environments. In addition, the influence of iron content on the fatigue crack growth rate (FCGR) of the weld overlay in both air and a sour environment was investigated. Weld overlays with a range of iron contents (5-36%), were examined. These weld overlays were manufactured using gas metal arc/metal inert gas (GMA/MIG) welding and gas tungsten arc/tungsten inert gas (GTA/TIG) welding techniques and the required iron level in the weld overlay was achieved by changing the welding parameters. SCC tests were conducted in 25%w/v sodium chloride (NaCI) solution containing H_2S and CO_2 (pH_2S=14 bara, pCO_2=28 bara) at 177°C. FCGR tests were conducted in air and in 25%w/v NaCI solution saturated with an H_2S/CO_2 gas mixture (pH_2S=0.4 bara) at ambient temperature and pressure.