Duplex and NACE MR 0175

[EuroWeld]

Hello all,

Currently we are designing a few hp heat exchangers including NACE MR 0175 requirements.
Materials of construction will be S31803/S32205 DSS, material thickness up to 100mm.

Most of the requirements that are included are understood and can be achieved but the maximal hardness raised some questions.
After studying the MR 0175 we noticed that the hardness requirements for DSS is no longer included in the latest edition(<28HRC previous version).
What would be the reason of this change? Can anybody help with important information that helps to ensure that also the welds meet the requirements of NACE.

Do we need to take into account a lower hardness value for base material (A182-F51)?
What should be our focus during welding (100 mm but welds) to comply with the requirements, this also includes tube-tube sheet welding?
Is it needed to perform a heat treatment (solution anneal and quenching) after welding?

We already have expierence with (welding) DSS, only this thickness including NACE requirements is new.
All help is welcome,

Thanks

 

[metengr]

I know that in the past there had been issues raised with not being able to achieve at or below 28 HRc in the duplex stainless steel weld deposit. Apparently, this requirement was relaxed because either more test data or industry experience surfaced which supported removal of the hardness restriction. This is a committee decision and they can revise the requirements at any time.

Heavy section duplex stainless steel welds can be difficult to weld because of restraint and heat input concerns. I would make sure that the heat input is carefully controlled, through rigorous monitoring of interpass temperature. Heat input needs to be adjusted for the heavy thickness.