51314-4289-Stress Corrosion Cracking Assessment of a Quenched and Tempered HSLA Steel in Two Alkaline Environments

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Product Number: 51314-4289-SG

ISBN: 4289 2014 CP

Author: Ali AlShawaf

Publication Date: 2014

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The heat exchangers (coolers) made of Quenched and Tempered High Strength Low Alloy ( Q&T HSLA) Steel developed multiple cracks emanating from the circumferential weld in the shell after a short time of service. Some of the cracks had grown through the thickness and thus started leaking. The failure has been diagnosed as Environmentally Assisted Cracking which is a general term for brittle mechanical failures that result from a combination between residual tensile stress susceptible microstructure and corrosive environment. EAC includes stress corrosion cracking (SCC) and hydrogen induced cracking (HIC). Slow Strain Rate Tests (SSRT) machine which is in connection with a high temperature/high pressure autoclave has been carried out using a Constant Extension Rate Test (CERT) machine. Stress corrosion crack testing of this quenched and tempered HSLA steel has been carried out from 50 to 180 °C at constant strain value in two basic environments at temperature ranging with the monitoring of the oxygen level. After the fracture of the specimen both stereoscopic optical microscope and Scanning Electron Microscope (SEM) were used to study the cracking morphology as a function of applied strain. To calculate the SCC susceptibility the plastic strain-to-failure (EP) and reduction in area (RA) were calculated from the stress-strain curve and the fracture surface of the broken specimens respectively. Results indicated that SCC susceptibility increased with increasing temperature increasing oxygen level and the percentage of salt in the solution. Better understanding of the SCC behavior of HSLA steels at higher temperatures and in basic environments allowed for the specification of application ranges that will avoid failures in future.