FINISHED VESSEL- CAN I WELD ATTACHEMENTS ?

[DORU]

Dear Sirs,
I have the following problem:
My Client has just received a new pressure vessel (Instrument air receiver) with MAWP 8 bar. The manufacturer did not wanted to weld a few attachements for sustaining a ladder but we still need these.
The vessel is primed, has 10mm thickness and was tested in the manufacturer's yard. It was not heat treated of course.
Can I weld 4 attachements for sustaining a vertical ladder ?
Where in ASME 8 can I find the rules concerning welds on vessels after delivery ? Please, can you help ?

 

[deanc]

The simple answer is no. See UG-99a1. The attachments could be attached under the "R" stamp.

 

[DORU]

I was hoping for this answer. Thanks a lot.
The vessel is not ASME stamped. How is this affecting the last phrase you said ?

 

[Heyner]

Hey, if your vessel is not stamped, your vessel is not an ASME vessel, being strict.

Now, if you need to attach a ladder, a good practice may be trying to do it without welding any connection, may be you can perform some kind of steel belt around the manhole neck, or something like that... And if you finally decide to weld it, try to follow the indications of code, using the same type of material, putting the lugs on a pad, et cetera. Anyway, it is not and it won't be stamped, but you can update drawings and so on...
Remember: if it is your vessel, and it is not stamped, it is your responsibility.

 

[aybee]

From experience in refinery service welding onto vessels after they have been delivered and after years in service is commonplace. Vessels are often fitted with new internal support rings for liquid spill trays and have brackets fitted to the outside for new walkways. If its not a main weld as part of then pressure envelope then the vessel is not re-hydrotested but the welding is all fully NDTested. this only applies to carbon steel vessels which have not been PWHT.Welding which affects the shell integrity usually requires a re-hydro but an addition of a nozzle may not, it would be 100% NDT, UT/Radiography and Mag particle. Some vessels are in locations which can support the weight filled with water so full NDT is used in lieu..Aybee

 

[jte]

DORU-

My experience is similar to aybee's. Welding on stamped pressure vessels (especially when they're in service) is avoided when possible, but it is not unusual either. Prior to striking an arc on a vessel, though, get a verbal approval from your AI. NBIC '92 (the latest legal edition in CA) lists adding things like ladder clips as a "repair of a routine nature" which doesn't require an R stamp.

From a Section VIII Div. 1 perspective, you will not require PWHT (I presume your air receiver is CS, probably SA516 material). Refer to table UCS-56 for P-No. 1 material. Note (2) specifies that if the *weld joint* is thicker than 1½" you must PWHT. Now go to UW-40 (f)(3) and you'll see that "For fillet welds, the nominal thickness is the throat dimension..." If you put your clips on with a ¼" (or even much larger) fillet, you'll have no code mandated PWHT.

If the vessel is PWHT for service (not likely for an air receiver!), what we've done is discuss with the metallurgist what the consequences of welding are. Let's say we have a relatively thick shell and we're adding ladder clips with a ¼" fillet on both sides. If we control the heat input, the steel temperature on the inside of the shell may be low enough to not impact the metallurgy which needed to be PWHT for service. Again, this is a call you must make in conjunction with your metallurgist (not just some guy who just happens to know something about steel).

With or without a Code stamp, you should have the same concerns - keep the darn thing safe. Since we have stamped vessels we need to jump through a few additional hoops to do this type of work. In your case, with no stamp, you just have to be comfortable that you're not impacting the safety of your equipment.

Let us know what you wind up doing!

jt

 

[hockchong]

Heyner,
Just want to clarified with you. You mention vessel without code stamp can't be considered as ASME vessel (to be strict).

For example, if a client mention they want ASME vessel without mentioning code stamp, is that mean they want "U" stamp vessel.

I have a case here where my client argue that what they mean ASME vessel is with code stamp.

BTW and clause in the code explain about these?

Thanks.

 

[aobjr]

Doru,

Check UCS-56 if you can weld without mandatory PWHT.

AOBJR

 

[chicopee]

Surface welding on PV's may be acceptable as long as integrity of pressure vessel is not affected.

 

[BJaffa]

IN Alaska, any welding to a pressure part must be performed by a Code shop. All requirements of the NBIC or ASME Construction Code must be followed. After delivery use only the NBIC which in current rules considers ladder attachements as non load bearing routine repairs. It would be up to the AI as to the level of inspection required. Just what constitutes a load is an engineering question.

 

[70577]

70577(petroleum)

Answer is yes! Only on after stress relief are you not allowed to weld an attachment or anything else as allowed by ASME CODE.

 

[dig1]

It is not a blanket statement that you cannot weld after PWHT.

Just went through an experience where a PWHT vessel had to have two large (36" square) pads for pipe hanger trunions (with a fair amount of load) added two days after field hydro (and U-1 stamping). The piping designer forgot to show them on the drawings. This is a sitution where the vessel would have been PWHT for service even if not required by the code.

Worked with the AI and our internal and customer's materials people and used one of the procedures in NBIC (RD-3010 if I recall) to have the pads installed without PWHT. The vessel was then R stamped. It wasn't inexpensive considering they were 130' in the air.

Each situation is unique and requires cooperation between all parties.

Going to the original question, follow the NBIC even if it is not required in your area; unless other local regulations prevail.

 

[deanc]

Good advice dig1.