Pressure Vessel Code Boundry

[nichols7007]

How can I establish where the boundry is for welding on an ASME Pressure Vessel? One of our clients has asked us if we could seal weld a 3/4" SA-105 extended-body valve to the mating 3/4" coupling(sample point), which is welded to the vessel shell. The coupling is shown on the U-1 and Manufacturer's Drawing. As noted the valve is currently threaded to the coupling, so the proposed seal weld would be the second weld from the vessel. Is this a code weld?

Please reference in the Code (ASME or NBIC) where I could find this information. Is it possible that this is a Jurisdictional issue?

 

[rumandcola]

U-1(e)(1) outlines the scope of a section VIII-i vessel. In your case "the first threaded joint for screwed connections". Your threaded connection is providing the mechanical strength. I would discuss this with your AI and the jurisdiction where this is installed before welding to a code stamped vessel

 

[jte]

The code scope ends with the threads which provide not only mechanical strength, but (if piping threads) also the fluid sealing surface.

The seal weld is a piping weld, not a vessel weld. Not a bad idea to chat with an AI or your jurisdiction (in California they’re at

http://www.dir.ca.gov/dosh/pressure.html)

just to check. Before you call your AI or jurisdiction, read up a bit:

Interpretation VIII-1-89-27R indicates that the term “completed vessel” means vessels on which no further welding will be done after the final hydrostatic test.

Interpretation VIII-1-01-127 indicates that a pipe can be threaded into a threaded fitting and seal welded after the hydrotest with no additional hydrotesting.

These two Interpretations together imply that the weld is not considered part of Div. 1. This is consistent with other interpretations which indicate that for a nozzle consisting of only a pipe stub which will be welded to piping in the field, the field weld, including weld metal, is considered outside the scope of Div. 1, thus the weld belongs to piping.

jt

 

[nichols7007]

Thanks for all your insight. I will discuss this further with our AI.