Underground pipeline steels have been proved susceptible to Transgranular Stress Corrosion Cracking (TGSCC) in diluted solutions of near neutral pH. Hydrogen embrittlement due to the diffusion of atomic hydrogen produced in the cathodic reaction at the crack tip has been proposed in literature as the active cracking mechanism. To reproduce cracking morphology observed in field, tests under load control have been performed and compared with Slow Strain Rate tests under displacement control. Three high strength pipeline steels of new production were examined (X65, X80, X100) and were found susceptible to TGSCC in a range of mechanical/chemical conditions. Their behaviour however was comparable with no clear dependence from the mechanical strength. The observed loss of ductility in environment is noticeably lower than the value in air. These results do confirm the presence of cracking mechanism due to hydrogen embrittlement. Both loss of ductility and crack velocity are dependent on opening velocity; the susceptibility to TGSCC was higher at opening rates lower than 5.10-6 mm/s. The SCC component of crack growth rate was an order of magnitude higher than the mechanical component (10-7mm/s) at the lowest opening rate investigated (10-6mm/s), in agreement with literature results.
Comparison of new high resistance pipeline steels with respect to TGSCC susceptibility
Vergleich neuer hochwiderstandsfähiger Pipelinestähle in Bezug auf TGSCC Suszeptibilität
2001
10 Seiten, 10 Bilder, 5 Tabellen, 11 Quellen
Conference paper
Storage medium
English
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