Hardness requirement in Sour service for (Duplex) Stainless steel

Section 7, Table 7-11 of DNV Standard OS-F101 October 2010 – Submarine pipeline systems – provides HV10 limits for weldments in 22Cr and 25Cr duplex stainless steels for line pipes. For 22Cr and 25Cr duplex, the hardness in the weld and HAZ shall not exceed 350HV10 and the base material shall not exceed 290HV10 for 22Cr, and 330HV10 for 25Cr. Section 6, paragraph B201 of DNV Standard OS-F101 October 2010 states that materials shall be selected for compliance with ISO 15156.

NORSOK Standard M-630 Rev.4 January 2004 – Material data sheets for piping – included material requirements in the form of a collection of material data sheets (MDS) for use in piping systems for the petroleum industry. These MDSs provided both HRC and HV10 limits for duplex and super duplex stainless steel. The limits for 22Cr duplex parent material, HAZ, weld metal were 28HRC or 271HB or 290HV10. The limits for 25Cr duplex were 32HRC or 301HB or 330HV10. However, this has now been superseded by NORSOK M-630 Edition 5 September 2010, which does not give hardness limits for duplex stainless steels, but refers the user to relevant standards. Similarly, NORSOK Standard M-601 Rev.3 January 2004 – Welding and inspection of piping – states in Table 2 that hardness of duplex stainless steel welds for sour service shall be below the following limits: 22Cr duplex 310HV10, 25Cr duplex 330HV10. However, the current M-601 Edition 5, 2008 has deleted maximum hardness limits for duplex and super duplex stainless steel.

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