Crack tip opening displacement (CTOD, δ) tests were carried out in buffer solutions, sand and clay to evaluate initiation of hydrogen stress cracking (HSC) at surface defects in buried pipelines under cathodic protection. Four series of line pipe steels and seam welds showed a similar tendency in cathodic current density (i) versus the critical CTOD (δC) curves, irrespective of types, pH and water content of the soils; δC showed a minimum (δHSC) when i>ith (ith≒1 mA/cm2) in all the testing conditions. The critical CTOD with cathodic protection, δHSC„ increased with increasing the critical CTOD in air, δC. HSC could initiate at surface defects in pipelines only when i>ith and δ ≧ δHSC.

Subject
Ambient conditions, Test methods, Water, Materials, Piping, Surface defects, Crack initiation, Pipelines, Acidity, Overprotection, Base metals, Stress, Steel
Keywords:
cathodic protection, crack tip opening displacement, fracture mechanics, hydrogen stress cracking, line pipe, maximum allowable defect size, pipeline, seam weld
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2000
Association for Materials Protection and Performance (AMPP)
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