Seal Welded Seat Rings

[Meqdadkhan]

Dear all,

With reference to API 600 Standard for steel Gate Valves (Thirteen Edition, January 2015) clause 5.3.3.4: “Threaded seat rings shall be seal welded; tack welding or stitch welding is not permitted”.

My question is, what are the implications if the seat ring was tack welded and not seal welded?

The subject clause is in direct conflict with my company standards.

 

[Compositepro]

My guess would be to prevent crevice corrosion and potential leakage.

 

[HitokiriAoshi]

Tack welding fails in-line, causing failure of seat, and downstream equipment. tack welds are basically never of quality, and should be considered no better than a feel good weld. Furthermore, a gate valve's full pressure against a seat, combined with other body stresses, can easily crack a tack weld with some corrosion help..

finally, threaded connection are highly prone to failure, which is why we require seal welding. way too many steam failure are past threaded connection.