Duplex stainless steel expansion coefficient value

The co-efficient of expansion in the CAESAR database for duplex stainless steel
(A790 S31803, 22Cr-5 Ni-3Mo) is the same as for austenitic stainless steel.

Per ASME BOILER AND PRESSURE VESSEL CODE, section II part D, table TE-1, for DSS
(group 2 material) this value is lesser than austenitic SS.

Does anyone have further understanding on this.

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