P91 TO SS 304 WELDING

[qualitypro]

What are the constraints while welding P91 to stainless steel small bore pipes? What should be the minimum preheat, maximum interpass temp and post weld heattreat temperature? Is an Inconel wire/ rod appropriate for producing a quality weld?

 

[davefitz]

You use a safe-end and have to avoid sensitizing the 304H by ensuring the P91-P91 PWHT zone is far from the 304H-incolnel HAZ.

According to Mannesman-Vallourec :

" the best way to realize a transition from T/P91 and an austenitic steel is by making a transition joint ( safe end) at the shop. First nickel-base weld metal is deposited on one side of a t/P91 piece followed by an NT treatment similar to T/P91 base metal. This transitio piece can tehn be welded on site to T/P91 and to the austenitic steel . The T.P91 side is a regular similar weld with matching consumables and local PWHT ( without heating and sensitizing the 304H), whereas the austenic side is welded to the nickle base weld deposit by using a nickel base consumable without PWHT. "