Abstract: Aiming at the failure case of stress corrosion cracking of steel No. 20 welded with over-matching J507 electrode under wet H₂S condition in petrochemical plant, this paper carried out the sensitivity test of the cracking of steel No. 20 welded with different matching electrodes in hydrogen sulfide corrosion medium. And it studied and analyzed the cracking causes from such aspects as the chemical composition of weld material, the strength, hardness and microstructure and so forth. The paper identified the reasons why the joints welded with over-matching J507 welding electrode for steel No. 20 are more prone to SSCC than those welded with equal matching J427 (or J422) welding electrode. In order to avoid the above problems, the paper puts forward relevant suggestions on equal matching base metal and welding material.

Key words: wet hydrogen sulfide steel No. 20, over-matching welded joint, sulfide stress corrosion cracking/SSC