TOPIC: Non-pressure Field Welds to C.S. Pressure Vessels

We're having a discussion as to whether or not a non-pressure attachment (pipe guide) can be welded to a carbon steel, unlined, non-PWHT pressure vessel. The answers range from "of course" to "never" to "only on the skirt". Please weigh in and provide reference specifications if you can.

Well the easy answer is YES ...and NO! "IF" this vessel is an ASME coded vessel, and after adding your modifications, your are NOT prepared to re-code the vessel (which cost some money) then the answer is NO! UNLESS you down grade that vessel to basically a zero-pressure container, which it remain in that classification the rest of it's life. Now I'm assuming that your adding a connection of some type ...Nozzel or coupling.
However if your adding some type of "support", as long as it's on the skirt area (or support leg) and not close enough to the main body (vessel containment) that the heat effected zone of the weld effectes that portion of the coded vessel, then YES. ...Clear as mud!??

Thanks! It's a pipe guide that we're thinking of adding.

Okay you are adding a Pipe Guide, but you do not say where you are adding it.
On the body of the vessel or on the non pressure Support (Skirt or Legs)?

Location was part of my original question. Some of our folks say only on the non pressure (skirt) portion of the vessel. Others say you can weld to the pressure vessel shell. This is the basis of my quandry.

You can put it anywhere you want, BUT there are "ramifications" to some locations ...as I indicated in my earlier reply about the ASME code issue. I personally had skirt vents added to and existing vessel they want to re-use in the oil fields. We were able to do this without re-coding the vessel because we didn't violate the coded main body of the vessel.
Now playing the devil's advocate and you wanted to added that pipe guide square in the middle side of the coded vessel, you can do that, BUT you'll have to do a PWHT to code, and maybe re-line the inside of the vessel if it had a lining. AND we're talking about alot of money to do it ...and I didn't even touch on the transportation cost.
You can do what you want, aslong as you got the money to cover the action. ...Just like every other thing in this world.