Experimental Characterization and Monitoring of Early Stage Corrosion Degradation of Pipeline Steels

Overview

Main Objective

Enhance pipeline safety through understanding the early corrosion mechanisms in high strength pipeline steels that lead to stress corrosion cracking with a focus on measurable degradation parameters that can guide the development of advanced NDE measurement procedures.

Public Abstract

The safety and reliability of gas and oil transportation pipelines requires fundamental scientific understating of the materials degradation processes, and technological development of detection and monitoring protocols and methodologies. One of these issues, relevant to materials reliability is the early stage detection of stress corrosion cracking (SCC) prior to rapid crack propagation, after which failure rapidly becomes imminent. For example 21 % of steel pipeline failures are attributable to SCC. During SCC, the majority of the life of a pipe remains within the nucleation stage wherein micro-damage is percolating very slowly and below detection thresholds for commonly deployable nondestructive evaluation techniques. An interdisciplinary team using a framework to understand the early corrosion mechanisms in high strength pipeline steels, leading to SCC under different hydrogen absorption levels with a focus on measurable degradation parameters that can assist in the development of new advanced NDE measurement procedures. The phenomenological understanding, and laboratory measurements of such degradation, will assist in the development of NDE and in situ measurement procedures for the detection and monitoring of the early stage of SCC. These insights will also enhance abilities to better predict remaining safe life, operating pressures and identify the need for mitigation measures to be taken, as highlighted in program area #5 "Design and Material". Among the many degradation mechanisms, corrosion reactions might produce atomic hydrogen that gets absorbed, diffused and entrapped within the metal. Defect generation near the corroding surface, whether related to hydrogen or the corrosion reaction itself, leads to increased internal residual stresses, localized plastic deformation and damage accumulation. These phenomena are all precursors to the initiation of SCC. An experimental protocol will be developed to characterize the residual stress buildup using in situ substrate curvature measurements. The accompanying material property changes (modulus and flow stress) of the near surface layer will be probed by nano-indentation and nano-scratch experiment after exposure. A 4-point AC/DC probe will be also incorporated to measure the changes in electrical resistance of near surface layer as a function of the corrosion environment and exposure history.

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