Mohammad Ali Mohtadi Bonab

The microstructure of API X70 pipeline steel was modified by applying different heat treatments including water-quenched, water-sprayed, and water-quenched and tempered. Hydrogen induced cracking behavior was investigated on the X70 steel at these heat treatments. Two test methods, Japanese Industrial Standard (JIS) and vacuum thermal desorption, were used to release hydrogen from reversible and irreversible traps. The experimental results showed that the highest amount of discharged hydrogen in reversible and irreversible traps was related to the water-sprayed and as-received steels. The hydrogen discharged content from reversible traps reached to a saturation level after 8 h of charging, and it decreased considerably when the steels were charged for 15 h and 24 h. Hydrogen discharge tests proved that a higher amount of hydrogen inside steel is not a reliable measure for HIC evaluation. HIC test results also document that the waterquenched steel with agglomerated martensite particles had the highest susceptibility to HIC. Texture study results show that a low fraction of important texture components, such as {023}, {321} and {332}, cannot be reliably used to evaluate HIC. As a result, a novel method of manufacturing of pipeline steels with an optimized texture is required to increase safety and reliability of transportation of sour gas and oil.