PWHT for API 650 Nozzles? 2

[ahp54]

As per API 650 requirements ,it is required to PWHT nozzles as the thickness of shell exceeds 1/2 inch and material group IV,my questions:

1 What is the idea behind prohibiting PWHT on tank after erection on tank?

2 Is it required to perform PWHT only in a furnace or we can perform it with PWHT machine in site before erection?

3. Is there any considerations that PWHT can be done after installation?

 

[fegenbush]

1. Field PWHT (even localized) is often cost prohibitive.

2. I suppose it is possible to PWHT in the field prior to installation, although I am not sure why you would want to do that.

3. Appendix D 650-I-01/00 is quite clear that PWHT must be performed prior to installation and that localized PWHT cannot be used. However, it is silent on the question if you were to PWHT the entire tank in the field. I can pursue this further, if you would like.

 

[IFRs]

PWHT in the field is prohibited as I understand it because there is restraint all around the nozzle assembly.

 

[ahp54]

fegenbush & IFRs, Thanks for the reply...the reason we want pwht to be done on site is that we already erected and welded the shell without the nozzles, we've done the erection to cope-up with the schedule but then we are having a huge problem. We are planning to cut again the shell but we need to submit proper procedure for cutting and re-installation. Do you have any suggestions for the procedure? This mistake was a big pain in the ass.

 

[IFRs]

Shop install the nozzles in a shell plate or thickened insert plate, PWHT and install the assembly in the tank. You'll have to cut larger holes in the shell plates but you'll be in compliance and more importantly you'll have a safe tank that does not increase the owner's risk. Schedule and cost is not a valid reason for not doing it right.

 

[fegenbush]

I agree with IFRs. If you don't have time to do it right, when are you going to have time to do it again?

 

[IFRs]

API 650 does condone thermal stress relief for the entire tank, so if this is an option for you, add it to your list of possibilities.