ABSTRACT
For some years, conventional 2¼Cr1Mo grade is less and less used for the fabrication of heavy refining reactors and is progressively replaced by 2¼Cr1MoV grade which offers much better mechanical properties at high temperatures. This change also offers large benefits on hydrogen resistance due to large differences in hydrogen solubility, diffusion and trapping behaviour between the two grades.
Focusing more deeply on differences between the two previously cited grades, it appears that 2¼Cr1MoV offers an important gain in terms of hydrogen resistance but has also a very complex behaviour, strongly depending on charging method used to introduce hydrogen in material. Trapping and diffusion behaviours are particularly different when hydrogen is introduced using autoclave charging (gaseous hydrogen as in refining industry), using sour service environment (aqueous hydrogen sulphide as in gas treatment industry) or using cathodic charging.
This paper proposes to explain the differences between the two previously cited grades when facing gaseous and aqueous hydrogen and then the consequences on fracture performance. This demonstration is based on actual hydrogen diffusion and solubility laws measurements associated to different kinds of mechanical tests.
