PWHT or not.

Date 03-20-2008 04:12

Greetings all,
Need some advice to see if we can get out of a very costly stuff up.
We had 4 LPG Bullets fabricated in India a few years ago. They are 33 metres long, 8 metres in diameter and they are 49 mm thick. Material is A516 Gr 60 and they are designed to ASME VIII Div 1 and have had PWHT.
Stiffening rings are also 49 mm plate with a 20 mm leg length fillet and they have approx 3" mouse holes cut in them. The very bottom ones are for drainage and the other 3 on each ring are where the stiffener crosses the longitudinal weld. There are approx 320 of them in total.
The weld symbol shown was to weld all around and some have been welded around the corner and others have stopped between 1 and 1 1/2" from the mousehole. Our engineering department has instructed us that we have to weld them all and locally stress relieve all of them. As you can imagine this will be charged back to the manufacturer but it will impact hugely on our schedule.
If we put a 6-8 mm fillet sealing run with an E7018 electrode would we have to stress relieve everything again based on ASME VII Table UCS-56 ?
If we do have to stress relieve do we have to have access to both sides of the shell ( These Bullets are buried up to halfway with backfill) or can we PWHT from inside only ?
Any help would be greatly appreciated,
Regards,
Shane

By new tito (***)

Date 03-20-2008 12:59

Shane,
If these were built by another manufacturer and you will be doing the repair work, I have a few comments - apparently these are ASME stamped, so I'm guessing the work you will be doing will be considered a "repair" and would/could fall under the NBIC and the "R" stamp. If this is the case, you can follow section RD of the NBIC and use the alternatives to PWHT. There are 5 "welding methods" that can be used in lieu of PWHT'ing the entire vessel. These 5 "methods" all have different stipulations, so you'd need to see which one suits your application. There is also para. RD-1100 that adresses local PWHT'ing using inductance or electric resistance heaters.

In any case, if you are a holder of the R stamp, i'm sure you know, but you would need to run all of this by your Authorized Inspector.

If this would fall under (I don't see how) ASME "U" stamp, then I think you would have to PWHT the entire vessel. The only way I can think of for you or your company to fall under ASME "U" stamp would be to have the original MFG consider the vessels a "PART" provided with applicable documentation, and then your company complete the work. Which then of course would make the entire vessel fall under your "U" stamp.

By jon20013 (*****)

Date 03-20-2008 15:20

Shane, unfortunately, I dont have access to my ASME VIII since I'm writing from home but speaking strictly off the top of my head, I would have thought that a 6 - 8mm fillet weld (functioning as a seal weld) should be exempted for this material, especially if a 200 or 250F preheat is applied. Please correct me if I've missed some point? As I mention, I'm speaking strictly from memory, which is not so good in older ages, lol!

EDIT: New tito brings some excellent points re NBIC.

By Shane Feder (****)

Date 03-20-2008 20:09

New Tito and Jon,
Thank you for your assistance.
Fingers crossed we can get it past our Engineering Department.
Have a great Easter everyone,
Regards,
Shane

By jon20013 (*****)

Date 03-20-2008 20:46

Shane, just a word of caution to your engineer's, and it relates to what new tito said; if your engineer's "force" you to weld on the vessel and it's a stamped vessel, the stamp will be void. You would need to coordinate with AI and do welding under a repair certificate. After your engineer's consider the possibilities, it might well be that they "see the light" and understand there are other ways to seal for corrosion purposes as the welds you mention would have no structural affect.