How to evaluate the microstructure of duplex stainless steels welding for NACE MR0175?
NACE MR0175, DNV-RP-F112, Norsok M630 and BS4515-2 are just some of the design codes and standards that require exhaustive examination of the microstructure of duplex and superduplex stainless steels. At Oil & Gas Corrosion we can help you navigate through these requirements to make sure your equipment and materials are fit for purpose.
If you want to learn more about duplex microstructure you can read one of our articles Duplex and SuperDuplex Stainless Steels, why is everyone so picky? the answer is HISC
ISO 15156-3, A.7.3–Regarding metallographic examination of the microstructure: a) Do closely spaced spheroidal precipitates such as grain boundary carbides constitute continuous precipitates? b) At what spacing would closely spaced spheroidal precipitates be considered continuous? c) Are the quantification of precipitates (intermetallic phases, nitrides, carbides) to be evaluated as a volume fraction relative to the bulk sample? d) In cases where only grain boundary precipitates are observed, is the quantification to be made as a volume fraction relative to the bulk sample or as a lineal fraction relative to grain boundary length? e) In the absence of intermetallic phases and nitrides, does 1 vol.% represent the maximum allowable carbide precipitate content? f) What is a suitable recommended practice or standard by which to perform this quantification?
a), b), e) For NACE MR0175/ISO 15156-3, A.7.3 it is the responsibility of the equipment user and the manufacturer to set the quantitative standard they wish to follow when this goes beyond the guidance given.
c), d), f) It is the responsibility of the equipment user and the manufacturer to agree on the method and acceptance criteria for the measurement of precipitates.
This is in relation to NACE MR0175/ISO 15156-3 A.7.3
Reference: ISO 15156 Maintenance Panel Inquiry #2005-28