The influence of external and internal factors on stress corrosion cracking of low-alloyed pipe steel
DOI:
https://doi.org/10.31471/2311-1399-2020-1(13)-8-15Keywords:
alternating wetting; cathodic polarization; low alloyed pipe steel; near-neutral environment; slow strain rate test; stress-corrosion cracking.Abstract
The article presents investigation results of the regularities of stress corrosion cracking (SCC) of controllable rolling X70 pipeline steel under the influence of various factors: corrosion-active environment, potential, pre-accumulated stresses, periodic wetting, etc. Factors, acting in the conditions of the gas pipe mains operation, were simulated in the laboratory conditions and their influence on the SCC susceptibility of X70 pipe steel was investigated. It was found that in NS4 solution, potential shifting to the cathode area promotes the increasing of the SCC susceptibility of X70 steel. Under cathodic protection at potential equal to -1.0 V, the fracture characteristics change, a brittle component appears in the fracture, and the coefficient KS increases compared to the breaking of samples without cathodic potential. Under such a potential there may appear some differences in the SCC susceptibility of X70 steel, which have a minor structural features: steel with less contamination of non-metallic inclusions is less susceptible to brittle cracking. Accumulated cyclic stresses, periodic wetting, the presence of coatings with different transient resistance and the stress concentrator promote the increase of the degree of SCC susceptibility of X70 pipeline steel at a potential of -1.0 V.
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