Material requirements in acidic environments (humidity H2S)
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In NACE MR 0175, why should the yield strength of materials exposed to acidic environments (with H2S present) not exceed 620 N/mm2, and why should the hardness not exceed Rc22? What’s the reason?
Because the hydrogen atoms in H2S can enter the interstitial spaces, microcracks are formed under the stress of pressure. If the hardness is higher than HRC22, microcracks will propagate, causing brittle fracture of the material. If the hardness is less than HRC22, the material undergoes plastic deformation and microcracks do not propagate.
The foam is excellent and covers all aspects; then why can’t the yield strength exceed 620?
It’s all to avoid stress corrosion cracking