A new understanding of intergranular stress corrosion cracking resistance of pipeline steel through grain boundary character and crystallographic texture studies

Mechanistic aspect of near-neutral pH stress corrosion cracking of pipelines under cathodic polarization

Hydrogen induced cracking (HIC) of API X80 and API X100 pipeline steels have been investigated in high pH carbonate–bicarbonate environment using slow strain rate testing (SSRT) method. It has been found that while both steels are highly susceptible to HIC, and diffusible hydrogen content is higher in API X80 than in API X100, the later steel is more vulnerable than the former at high (more negative) cathodic potential. This higher susceptibility can be primarily attributed to the combined effect of (1) separation of bainitic lath boundaries due to hydrogen trapping in these locations, (2) mobile hydrogen, and (3) stress. The charging–discharging experiments followed by SSRT experiments in air suggest that, the cracks that appeared due to lath boundary separation did not cause the reduction of ductility by themselves, rather it was the diffusible hydrogen that forced these cracks to propagate and, ruptured the steel with very low percent reduction of area (%RA). Despite the fact that the mobile hydrogen content plays a key role in causing the embrittlement, the large number of cracks in API X100 steel, resulting from the bainitic lath boundary separation at high cathodic potential, superseded the effect of higher diffusible hydrogen content in API X80 steel. The general conclusion is that bainitic lath type microstructure is more vulnerable to HIC at high cathodic potential than the ferritic/granular bainitic ones. It has been also found that applying cathodic protection can lead to excessive hydrogen embrittlement in both of the abovementioned steels in high pH carbonate–bicarbonate environment and, therefore, efforts need to be invested in developing nobler (more positive corrosion potential) and better HIC resistant steels.

Effect of bainitic microstructure on the susceptibility of pipeline steels to hydrogen induced cracking

Local additional potential model for effect of strain rate on SCC of pipeline steel in an acidic soil solution

This work investigated the effect of plastic deformation on the electrochemical and stress corrosion cracking (SCC) behavior of X70 steel in near-neutral pH environment. The deformation-induced increase in electrochemical activity, dislocation density and heterogeneity, and surface roughness accelerated the corrosion, especially the cathodic reactions. Hydrogen absorption and permeation into the steel is promoted by the plastic deformation, resulting in the high hydrogen content of the pre-deformed steels. Moreover, the SCC susceptibility increases with plastic elongation, which is attributed to the enhanced anodic dissolution and hydrogen absorption.

Effect of plastic deformation on the electrochemical and stress corrosion cracking behavior of X70 steel in near-neutral pH environment

This paper provides an overview of mechanisms for high-pH and near-neutral-pH stress corrosion cracking of underground pipelines. Characteristics and historical information on both forms of cracking are discussed. This information is then used to support proposed mechanisms for crack initiation and growth.Copyright © 1996 by ASME

Mechanisms of High-pH and Near-Neutral-pH SCC of Underground Pipelines

Mechanisms of high-pH and near-neutral-pH SCC of underground pipelines

External stress-corrosion cracking of pipelines is a serious problem for the gas transmission industry. Longitudinal cracks initiate on the outside surface of the pipe and link up to form flaws that, in some cases, can lead to pipe rupture. This paper presents a model that quantifies the effect of stress-corrosion cracking on pipe failure stress. The model is an extension of those that have been developed for oil and gas pipelines and considers both flow-stress and fracture-toughness dependent failure modes. A methodology also is presented to calculate the remaining life of a pipeline containing flaws of known size.

Brent A. Harle

Papers

Mechanisms of High-pH and Near-Neutral-pH SCC of Underground Pipelines

Mechanisms of high-pH and near-neutral-pH SCC of underground pipelines

Effect of stress corrosion cracking on integrity and remaining life of natural gas pipelines