Dear Zamani, Please take this note that MR-175 is the material requirements, which defines condition fo rthe material selection for the wet H2S corrosion. There are additional requirements which are also been adopted. TM-0284 is the testing method which describes the test method for HIC suitability and the acceptance criteria. The listed below are the conditions which are taken into account while designing the materials for the vessels under wet H2S corrosion ( for the carbon steel materials) 1. Tensile strength < 590 Mpa ( SA-516 Grade-65 is preferred) 2. Hardness of the material < 18 HRC 3. S<0.003% 4. P<0.015% 5. Carbon equivalnce < 0.38 6. Steel making practice - Si killed steel 7. HIC testing as per TM-0284 and acceptance criteria ( this is applicable when the H2S content is more than 50 ppm) 8. UT - Lamellar testing of the rolled products(plates) as per the SA-578 with zero defect. 9. PWHT 10. Ni content of consumable < 1% Let me have your feed back if you need further clarifications. Regards, Shabbar Hussain Refinery Corrosion Engineer