51316-7629-Effect of Iron Content on Corrosion Resistance of Ni-Cr-Mo Alloy Weld Overlays in Corrosive Environments

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Product Number: 51316-7629-SG

ISBN: 7629 2016 CP

Author: Qing Lu

Publication Date: 2016

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Corrosion-resistant weld overlays are often used to improve the service life of components made with an otherwise corrosion-prone material such as carbon or low alloy steels. A major concern for overlaying by arc welding techniques is iron content and the way it influences corrosion resistance.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 in H2S 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 the gas metal arc (GMA/MIG) welding and gas tungsten arc (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 (NaCl) solution containing H2S and CO2 (pH2S=14bara pCO2=28bara and CO2) at 177°C where FCGR tests in air and in 25%(w/v) NaCl solution saturated with a H2S/CO2 gas mixture (pH2S=0.4bara) at ambient temperature and pressure. The results indicated an opportunity for relaxing the current permissible limits (typically 5%) for iron in Ni-Cr-Mo alloy weld overlays.Key words: weld overlay iron content stress corrosion cracking (SCC) FCGR H2S environment.