nozzle intersect circ weld question 1

[airtight]

We are looking at purchasing a vessel which has been constructed to an italian RINA code approx 20 years old.

We have found that it has a 2" nozzle which intersects the main circ weld from rolling to dished end.

Rina were not bothered but i am wondering where we would stand with ASME or even just good working practise ?

maybe someone can enlighten me? Thanks. Neville

 

[metengr]

airtight;
I don't see this as a problem of design. (see UW-14 in Section VIII, Div 1, Part UW of ASME B&PV code). If you have not considered this already, make sure you have performed your due diligence in terms of obtaining the prior operating history, maintenance and repair records of this vessel. In addition, you might want to perform your own RT, UT and MT inspections of the vessel welds and appurtances.

 

[jte]

airtight-

I agree with metengr. While it is desireable and good practice to avoid putting nozzles through welds, sometimes it has to be done. Provided that the due diligence is provided it shouldn't be an issue. With a used vessel, I'd consider calling for a few RT's of the area around the offending nozzle and use UW-14 as a guideline for an acceptance criteria. I'd be a bit more concerned if it was a longitudinal seam, but either way, the answer's the same.

jt

 

[chicopee]

You did not specify the type of rolled head. Any head with knuckle can not have an opening thru the knuckle. Thru circumferential weld only it is ok per UW-14.

 

[jte]

chicopee-

Care to let us know what part of VIII-1 or VIII-2 supports your statement about openings through the knuckle?

jt

 

[airtight]

Thanks for the remarks guys. It is not under asme juristiction but I was really keen to know what you would think about it. The nozzle does not need to be on the weld intersect, as there is plenty space elsewhere. Anyway we will do some ndt as there are a few other questions over the vessel. It is actually a large diving chamber / pvho so it will get a look over by a Lloyds and possible a DNV surveyor. Thanks for your help guys, another question comming soon ! Neville

 

[chicopee]

jte- I dont have the code with me, however, historically this has been the case-dont get in the knuckle. I have a little bit of time now,so, I'll research it and get you the references.

 

[chicopee]

JTE- perusing thru my archives (kicked my self for giving out most of my codes), I found an older ASME power code I: paragraph 29.11.1 will bear what I said above; obviously there is an exception with small piping connections. Altho this is not the reference you stated, from my past experiences with these codes (ASME I and VIII) I remember that there are very similar in content and format, therefore, under dished heads you may come across a statement "...by the corner radius..." which infers knuckle.

Knuckles under repeated cyclic loads are prone to cracks and various P.V. literatures recount leaks in these highly stressed areas. NBIC forbids repairs in knuckles but with trepidation allows such repair in well equipped shops.
With this background, this is the reason that I stated to stay awy from knuckles.