ASME B16.9 Welded vs Semless Cap

[Headache2013]

Dears;

As per my humble experience in righting piping spécifications, when a big size is selected to be welded type (not seamless), the fittings (elbow, tees, reducers) shall be also welded type (not seamless).
However the cap to select shall be seamless.
Does some know the reason of this exception: why caps can't be welded type? and why the standard ASME B16.9 doesn't give any indication about this subject.

Best Regards

 

[Surachai]

In my opinion,ASME B 16.9 products can be either seamless or welded and are typically made of pipe or plate therefore the fittings will include the seam or seamless as their origin product form. Cap is seamless because it made of plate. Caps (ASME B 16.9) used for a Code pressure vessel can't be welded since the head (cap) contained with the welded joint must be manufacturered by a Certificate Holder, eg. with U designator.

 

[Headache2013]

Sirs;

My pipe specification is as follows:

Pipe 18" to 36": API 5L Grade B SAW
Elbow, Tee, Reducer: ASTM A234 Grade WPB-W Weld ASME B16.9 BW
Cap: ASTM A234 Grade WPB ASME B16.9 BW

My question is: why the cap material is A234 WPB and not A234 WPB-W?


Best Regards.

 

[Surachai]

If the cap is seamless construction, it's marking shall be WPB otherwise WPBW which is welded construction.

 

[Headache2013]

my question is: why among all fittings , only the cap is seamless. Why it is not welded?

 

[XL83NL]

Not sure if its only available as seamless, but think about the manufacturing process of several types of fittings for a second.
Then ask yourself the same question again.

I could only think of very huge (maybe 60" and beyond) B16.9 caps being made of two plates welded together and hen formed. But then Again, such specials might be outside the scope of B16.9 and made according other industry practices.

 

[OSIRIS7]

They will probably be pressed in a die out of a plate. When the size of the cap becomes that large that plates have to be welded together before pressing in the die, it will be welded. However, those sizes will probably be called a head then.

 

[XL83NL]

@OSIRIS7; same as I said, different wording.

 

[OSIRIS7]

I know. Some people just need a different approach to get the picture. (No offence to anyone).

 

[racp12]

Dear Colleagues,
According to ASME B16.9, para. 1.3, there is no any objection for longitudinal seam fabricated fittings, moreover, there is no limit for quantity of seams.
My concern is about testing, taking into account that tests mentioned under sections 9 DESIGN PROOF TEST and 10 PRODUCTION TESTS, make no mention to weld quality