P91 to Cs (Temporary Caps)

[Percosta]

I need to Weld some temporay cap`s in Cs to P)1, just for Hydro Test purpose. I known that the temperatura of PWHT of the two materials are different and it´s not recommended this type of joint, but since it´s a temporary Weld that will be cut there are any suggestions?

Thanks in advance

 

[metengr]

The problem is that Grade 91 base material is very susceptible to stress corrosion cracking in the hardened condition from welding and exposure to moisture, which will be the case for your application for a hydrostatic test. If you cannot locally PWHT the temporary attachment weld I would look at mechanical plugs, in lieu of welded plugs, for hydrostatic testing.

 

[racookpe1978]

Concur with above.

See, you are trying to verify absolutely to the certifying agency and to the owner that ALL of the metal is strong enough to hold 1.5 the maximum working pressure during the hydro, right? So you are going to do that certification by damaging the metal that you are trying to certify?

(The permanent damage by the welding to the permanent steel won't be removed when the temporary weld is ground off, and that "temporary" bad weld WILL still be holding the 1.5 MAWP pressure during the hydro, so it has to be even stronger than the permanent steel.)

Do you think you will completely remove the bad weld, surrounding bad (damaged steel), after the hydro? If so, what will complete the pressure vessel boundary later? Another weld joint to the permanent cover or fitting? That would require another 1.5 MAWP hydro!

 

[weldstan]

We always PWHT the subject temporary weld. We also try to avoid using C.S. pipe caps and use WP11 or WP22.

 

[Percosta]

After i remove the cap`s, my intention it´s cut off the HAZ of the P91 base metal, re-weld for the final components, PWHT and perform a hardness test. These welds will be Golden welds. My question is: following this procedure which will be the better choice for the welding material: P91, P22 or CS?

If i choose the P91, and PWHT i will be behind the Tcrit. of the CS, and my affraid it´s the damage that i can input to the CS Cap, and have problems when i expose that material to 2500psig(Hidro test Pressure).

If i choose CS welding material and PWHT with the temperatur of the CS, i will have the P91 side with a value of hardness for outside the máximum admisible value.

Your comments it will highly appreciated.

Thanks

 

[metengr]

As weldstan mentioned above, use WP11 or WP22 caps in lieu of CS caps. Do it right.

 

[pandithan]

we use P22 materials only