PWHT SOAK TIME CALCULATION

[roca]

Pressure Vessel 100mm thick + 3mm thick SS cladding.

For calculation of the soak time does the 3mm thickness need to be taken into account?

e.g. calculate soak time on 100nmm or on 103mm?

 

[metengr]

You need to review UW-40, specifically UW-40 (f) in ASME Section VIII, Div 1.

 

[vesselguy]

roca,

please correct me if I'm wrong, but pwht is the heat treatment for the welds of the base metal. On this basis, code PWHT requirement, which exludes process consideration, is entirely on the thickness of the base metal joint for the type of metal in consideration. Hence, the soak time does not consider cladding thickness or W.O. thickness. That is my experience on the equipments I've done (including Cr-Mo thickwall vessels), so far. Others may know more.

 

[DVWE]

Can I just ask what difference it makes? 100mm = 3.93" and 103mm = 4.0", either way, 4" would be used, wouldn't it?

I believe if the vessel was designed with cladding strength calculated in the stess values, then it is part of the vessel thickness and must be accounted for. Most vessels are designed without doing this, so it is typically only the thickness of the base metal uncladded which is used.

 

[vesselguy]

DVWE,
cladding strength is never included in the base metal strength.

 

[DVWE]

vesselguy,
Have you read part UCL? Perhaps you can enlighten me...

 

[roca]

Thanks Guys

vesselguy - yes the SS is for corrsoion purposes only and the PWHT os for the welds. I have never before added the cladding thickness to calculate soak times, someone here in the office questioned it.

DVWE - I agree with vesselguy in that cladding strength is never included in the base metal strength and I have never worked for an end user who has wanted it any other way despite what part UCL states.

 

[DVWE]

Neither have I, but something to keep in mind.