PWHT requirement of shell plate buttweld for API 650 tanks if simulated PWHT required for plates

[Muza33]

Dear Experts


we are constructing crude oil storage tanks as per API 650, Now as per my understanding PWHT is only applicable for nozzle openings as per API 650,not shell buttweld, but now in drawing it is mentioned supplementary requirement for simulated PWHT of mechanical test coupons for our pate grade ASTMA 537 CLASS 2,MY concern is that since mechanical properties are to be checked on simulated PWHT coupons ,does it mean all my shell buttweld also need to be PWHT done?

kindly share your expert views and expertise

 

[Dhurjati Sen]

The tank does not have clean-out doors? Those are the only locations where you need to carry out PWHT.

DHURJATI SEN
Kolkata, India

 

[Muza33]

yes it have clean out doors, and same will be done PWHT as per API 650 requirements as well as if any nozzles applicable as per API 650 requirements ,


my concern was why Simulated PWHT is done in test coupons and mechanical properties evaluated ,if we are only going to do PWHT only in nozzles and not in shell welds(long seam and circumferential seams)

just had a internal discussion in department, and conclusion was simulated heat treatment was done to ensure mechanical properties during PWHT OF clean out doors or other nozzles as per API 650 requirements and not considering shell welds(long seam and circumferential seams).

Thanks for reply

 

[Geoff13]

I would order a standard set of test coupons to represent the majority of the shell that is not PWHT'd.

I would order a second set of test coupons with simulated PWHT to represent the plates used in the FTCO that are PWHT'd and the plates with large nozzles that are PWHT'd.

Thus many of the upper rings will only have standard test coupons without simulated PWHT.

In addition, for the A537 Class 2 plates that will be PWHT'd I would specify a minimum tempering temperature above the top of your PWHT range to avoid losing the temper during PWHT.

Since you've mentioned it a couple of times, API 650 does not require PWHT of the shell vertical or circumferential welds. It only asks for PWHT of the FTCO and nozzle assemblies.

 

[Muza33]

Thanks for explanation,


can i assume FTCO is abbreviation for clean out doors.

 

[Geoff13]

FTCO = Flush Type Clean Out

Been using it so long at work didn't realize it wasn't a standard acronym.

 

[IFRs]

A537 Class 2 is an API Group VI material. If your shell is over 1/2" thick than all nozzles over 2" need to be in PWHT assemblies prior to being welded into the tank. I'm sure you knew that but just wanted to be sure.