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51313-02120-Unusual Corrosion and Stress Corrosion Cracking on a Pipeline

Product Number: 51313-02120-SG
ISBN: 02120 2013 CP
Author: Jeffrey Xie
Publication Date: 2013
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$20.00
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An in-line inspection run uncovered a large number of anomalies in one joint of a pipeline. A subsequent dig revealed external corrosion resembling flower/fish-bone type morphologies. Grinding of the corrosion exposed crack-like damage to the pipe. The concerned pipes were cut and replaced. An investigation was conducted to understand the nature and mechanism of the corrosion/cracks on this concerned pipeline. Detailed investigation included metallurgical analysis of the concerned pipe segments identification of the corrosion products and characterization of the surrounding soils.

Corrosion on the surface was revealed to be cracks in the bulk of the pipe once the steel was polished to remove the surface. Cracks/corrosion on this pipelines demonstrated fish-bone type morphologies. Primary cracks aligned in the axial direction and secondary cracks aligned in the circumferential direction of the pipes. The cracks on the cross-sections were relatively wide and blunt very shallow and microscopically transgranular.

MnS inclusions with fish bone type morphologies were found in the pipe steel associated with the corrosion/cracks. In addition the inclusions were also enriched with Si and Al.

The unusual corrosion on this pipeline was thus determined to be corrosion and subsequently stress corrosion cracking (in the form of near neutral pH SCC) developed along the MnS inclusions which had fish bone type morphologies. Therefore this resulted in an unusual flower/fish bone type appearance of corrosion on the surface.
 

An in-line inspection run uncovered a large number of anomalies in one joint of a pipeline. A subsequent dig revealed external corrosion resembling flower/fish-bone type morphologies. Grinding of the corrosion exposed crack-like damage to the pipe. The concerned pipes were cut and replaced. An investigation was conducted to understand the nature and mechanism of the corrosion/cracks on this concerned pipeline. Detailed investigation included metallurgical analysis of the concerned pipe segments identification of the corrosion products and characterization of the surrounding soils.

Corrosion on the surface was revealed to be cracks in the bulk of the pipe once the steel was polished to remove the surface. Cracks/corrosion on this pipelines demonstrated fish-bone type morphologies. Primary cracks aligned in the axial direction and secondary cracks aligned in the circumferential direction of the pipes. The cracks on the cross-sections were relatively wide and blunt very shallow and microscopically transgranular.

MnS inclusions with fish bone type morphologies were found in the pipe steel associated with the corrosion/cracks. In addition the inclusions were also enriched with Si and Al.

The unusual corrosion on this pipeline was thus determined to be corrosion and subsequently stress corrosion cracking (in the form of near neutral pH SCC) developed along the MnS inclusions which had fish bone type morphologies. Therefore this resulted in an unusual flower/fish bone type appearance of corrosion on the surface.
 

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