Table UW-12 ( Single V and Double V clarifications)

Osama · **Joined:** Thu Apr 02, 2009 9:38 am **Posts:** 59

We are designing heat exchanger of shell of thickness = 30 mm and there are various circumferential and longitudinal joints.

My understanding according to code and Table UW-12 is

Type No 3 says: " Circumferential butt joints only, not over 16 mm thick and not over 600 mm outside diameter for single welded butt joint without use of backing strip"

According to above clause, i am sure that over 16 mm shell thickness and over 600 mm shell outside diameter we cannot use single welded butt joint (i.e. single V type joint) and therefore we have to use double-welding (i.e. double V type joint).

Please verify.

Please help me my friend.

Best regards
Osama

akonrad · **Posted:** Thu Apr 16, 2009 11:16 am

Osama,
You are going a bit too far with your interpretation. All it means is that you can't use Type 3. You can use Type 1 or 2. Type 2 has further limitations, but Type 1 doesn't have to be double welded- it just has to be accessible for visual inspection to demonstrale compliance with UW-35. Depending on your material of construction, all you have to do is choose a welding technique for root pass that will give you a nice root surface (GTAW preferable for most of steels), and here you go: your design engineer will be happy with his E increased from .6 to .7, your AI will be happy with extended scope of inspection (higher safety!), your client will be happy with possibly lighter vessel, your boss will be happy with decreased costs...

Osama · **Joined:** Thu Apr 02, 2009 9:38 am **Posts:** 59

Dear Sir,

What i understand from your email,

" We can also apply Type 1 (i.e. Single Welded Butt Joint Configuration or Single V) on our exchanger circumferential joints conforming UW-35 requirement"

Shell plate material is A 387Gr 11 CL-2 (1.25Cr 0.5Mo)

Please confirm
Osama

akonrad · **Posted:** Fri Apr 17, 2009 1:29 pm

Sorry, I have no experience with this material. The bottomline is you have to visually inspect root surface of the weld from inside of the vessel. This means you need a manhole or other ways to do it (with boroscope if your AI is happy with it).
What is your intended welding technique to make the root pass?

Osama · **Joined:** Thu Apr 02, 2009 9:38 am **Posts:** 59

Sir,

We will use TIG for root pass.

Actually we are fabricating this heat exchanger at our facility (in-house project). Also as a designer, I believe that with single welded butt joints , thickness = 30 mm (SA 387 Gr 11 Cl-2) and conforming requirement of UW-35, the inspection scope will be extended and therefore difficult to satisfy.
_______________________________________________________________________________

Ref: Type-1 (Table UW-12), the code doesn't say anything clearly about Single Welded Butt Joints.

The code says:
“By other means which will obtain the same quality…………..”
_______________________________________________________________________________

From Code, I understand that if thickness is > 30 mm and shell ID > 600 mm, the weld doesn’t have to be compulsorily double welded (You also agreed) and therefore the option left is single welded circumferential joints as discussed above. Please confirm.

Regards
Osama

akonrad · **Posted:** Tue Apr 21, 2009 10:57 pm

Yes, Osama, that's how I understand it: Table UW-12 allows you to make a sigle welded butt joint of Type 1. But do contact your AI, it's his opinion that counts here. And, of course the strength of your arguments :-)

Osama · **Joined:** Thu Apr 02, 2009 9:38 am **Posts:** 59

Dear Sir.

I am satisfied. Thanks once again.

Dr. Koelbl · **Posted:** Sat Apr 25, 2009 8:05 am

Osama,

with the material and thickness you are using, FULL RT is mandatory anyway. That will make your weld a Type 1 by definition. On the film you can verify that the UW-35 requirements are met. Problem solved.

DK

akonrad · **Posted:** Sat Apr 25, 2009 9:58 am

Dirk, spot on! A perfect point. In SecVIII's logic, RT demonstrates fulfillment of geometrical requirements. Go figure!

Osama · **Joined:** Thu Apr 02, 2009 9:38 am **Posts:** 59

Dear Sir,

Last question plz.

Our design and fabrication team has now decided to apply single butt welded joints (Type-1 i.e. RT 100 % and compliance to UW-35).

One small thing to confirm, is there any relief in meeting conditions of UW-35 and doing single butt welding at all circumferential joints other than RT issue. Sir can you state some reference regarding any concession in meeting requirements of UW-35 when single welded butt joints are produced.

Table UW-12 ( Single V and Double V clarifications)

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