duplex ASME VIII div. 2 2

[marc1000]

Does anybody know why duplex stainless steels aren't allowed/mentioned in ASME VIII div. 2? Is there a specific technical reason for or hasn't anybody had the need for that?

 

[LSThill]

Do you Mean RE: 2205 Duplex SS (S31803), (UNS S31803)

 

[marc1000]

Isthill,

UNS31803 among all the others; in table AHA-1 there is not one duplex stainless steel mentioned. Only austenitic and some martensitic and ferritic stainless steels.

 

[metengr]

The duplex stainless steels are limited as to their service temperature range because they can form sigma phase or other intermetallic phases that can significantly reduce toughness.

The approximate useful service temperature range I have seen published for duplex stainless steels are -50 deg C to 280 deg C. If I had to guess, this is probably the reason for not endorsing these materials in Div 2 applications.

 

[marc1000]

metengr,

I know the limitations of duplex SS: low temperature toughness and possible embrittlement at long exposure time to temperatures around and above 475°C. But is this a reason not to incorporate this into ASME VIII div. 2? In Div. 1 f.e. the use of UNS 31803 is also limited to 600°F.

 

[metengr]

marc1000;
My reasoning for limiting the duplex ss is based on the statements in AG-100 (Scope) particularly paragraph e. Div 2 deals with vessel design related to high pressures and it may well be that a more conservative approach is being used to restrict materials, in comparison to Div 1 rules.