Laboratory Testing in Leachate Environments to Understand Stress Corrosion Cracking on an Insulated Above Ground Pipeline

A comprehensive metallurgical investigation of multiple externally-initiated in-service leaks on an above-ground insulated oil emulsion pipeline concluded that the likely crack-initiating mechanism was stress corrosion cracking (SCC). However the SCC investigated herein occurred on an above-ground pipeline which necessitated a closer evaluation of the mechanisms and assumptions that are commonly associated with classically identified pipeline SCC. As such it was not clear to what extent the classic mechanistic principles of SCC identified on below ground pipelines were applicable to the current instance of SCC if at all. A root cause analysis (RCA) was used to identify the likely contributors to the SCC from stress environment and materials perspectives as it pertains to this carbon steel pipeline. As part of the RCA testing and chemical analyses were performed to reproduce the cracking in a laboratory environment. The purpose of the laboratory testing was to (1) reproduce the external cracking found in the pipeline and (2) evaluate the effects of insulation source electrolyte concentration and temperature on the SCC behavior of pipe steel in laboratory-produced leachates. Testing primarily consisted of cyclic potentiodynamic polarization (CPP) tests and slow-strain rate (SSR) testing using leachates solutions made from pipe insulation. This paper outlines key findings from the laboratory testing and a current understanding of the primary environmental contributors given that SCC on above-ground insulated pipelines is not commonly identified.

Product Number: 51319-13438-SG
Author: Kevin Ralston
Publication Date: 2019
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