The Susceptibility of Process Equipment and Steels to Cracking in Aqueous Hydrogen Charging Environments
March 27, 2019
R. Kane, Ph.D., M. Prager, Ph.D.
Number of Pages
WRC Bulletin 569 addresses several activities that have been initiated to better understand cracking due to hydrogen charging associated with corrosion of refinery process equipment. Included in this WRC Bulletin are results of a survey by NACE, details of an API/MPC program on Monitoring and Modeling of the cracking in a pressure vessel and results of a systematic laboratory study of test methods which might be used to determine the effects of variables on susceptibility of steels and welded process equipment. In the course of the latter program, test methods were examined and the influence of welding variables, steelmaking practices and microstructure were explored.
The MPC program covered various forms of hydrogen cracking ( , etc.). The program was needed because there was no consensus regarding the suitability of test methods for rating or ranking steels in terms of their suitability for specific applications. Likewise, industry did not have enough guidance as to the significance of welding heat input, microstructure, applied stresses and other variables so that materials selection, purchasing, design, fabrication and inspection of equipment could be optimized. The program was given increased impetus by the emergence of advanced (low and ultra-low sulfur) steels for these applications. There was urgency because of the need to inspect, repair or replace the growing list of equipment which had cracked or blistered unacceptably.
As a result of the program:
1) test methods have been improved and made more reproducible or relevant,
2) a practical test procedure which can be varied in terms of severity has been demonstrated,
3) the strategy for inspection can be improved,
4) the relative susceptibilities of steels may be determined,
5) cautions or concerns regarding the suitability of advanced steels for severe service have been identified,
6) the effects of design and fabrication variables are better understood,
7) the roles of microstructural variables on performance are clearer.
While additional refinement of the test methods used in MPC's program is in order, it is now possible to tailor testing of materials to specific process demands or fabrication plans.