The effect of post weld heat treatment (PWHT) was studied on a variety of microstructures of the pressure vessel steel (ASTM A516) ranging from the ferrite/pearlite to the tempered bainite obtained by different cooling processes. The hydrogen trapping behavior in sour environment was investigated by means of the electrochemical permeation technique and the modified JIS Z3113 method. The ISO17081 standard was used to evaluate the hydrogen trapping in the electrochemical permeation experiment by measuring several hydrogen permeation parameters such as the apparent hydrogen diffusivity (Dapp), the permeability (JssL) and the apparent hydrogen solubility (Capp). As the microstructure changed from bainite to ferrite/pearlite and also after tempering and PWHT, the value of Dapp showed a continuous increase while the value of Capp showed a continuous decrease. The value of Dapp was maximum whereas the value of Capp was minimum for all the specimens after PWHT. It suggests that proper PWHT is essential to control the number of reversible trapping site of hydrogen by obtaining the microstructure and low interfacial area of the spheroidized carbide caused by the agglomeration and growth of the fine carbide particles.

Subject
Constituents, Steel surfaces, Hydrogen permeation, Carbides, Microstructure, Diffusion, Iron sulfides, Diffusible hydrogen, Steel, Ferrite, Tempering, Hydrogen, Oil
Keywords:
pressure vessel steel, sour environment, hydrogen trapping, electrochemical hydrogen permeation method, post weld heat treatment, diffusible hydrogen
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2011
Association for Materials Protection and Performance (AMPP)
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