Safety Relief Valves

If thats what a client wants, give it to him. If want to know why, ask the client. You can just weld a ANSI 150 to an ANSI 300 with ou a piece of line. If's to hard to weld, you can put a 6" piece of pipe between them. To meet API 520, I'd keep the pipe between the two flanges to under 5 pipe diameters. Or use the calculations in API 520 to calculate maximum lenght of pipe.

No problem, the piping and vessel engineers were used to face this problem many times. And for this reason, the vessel designers take this note into consideration during the 1^st stage of vessel design.

1. If it is possible to reweld a flange with rating 300# into the nozzle of vessel, it will be good, may be you need to repeat the hydraulic test.

2. If the vessel is Code stamped, and no way to reweld, you can use a spool of pipe with 2 flanges, one rated 300# and other 150#.

3. The 3^rd solution, may be you ask for a new PSV with inlet rated 150#.

Some people have had problems sealing 150# flanges especially if there are temperature excursions so some companies just make it an arbitrary policy, which is their option. 300# rated flanges are heavier and seal better because they are stiffer and have better bolting so many process people require them even if isn't required by the process pressure & temperature. If your ASME Code vessel already has a 150# rated flange on it and the data report describes the nozzle as having a 150# flange, you're pretty much stuck with a 150#-300# adapter. Your customer probably won't be happy because you're only moving the problem from one place to another. If the data report does not identify the flange on the nozzle, then the flange can be replaced. The data report defines the limits of the vessel and the vessel actually stops after the first weld connecting the nozzle to the vessel. If the flange is a studding flange or a weld neck welded directly to the vessel wall, your sunk. If the nozzle is a pipe welded to the vessel and the flange welded to the pipe, the flange can be replaced without affecting the "codeness" of the vessel.

HI Morgan,

Your info is very useful. I will come back to you after I solve this problem with min damage.

Thanks a lot,

natarajan

I can echo from personal experience the superiority of class 300 Vs class 150 flanges for leak avoidance, even when not required by code.

Can you direct me to the paragraph or section in the ASME code defining when the flange on a nozzle can be replaced without considering it part of the vessel.

Maybe it was the conservative nature of the organization I worked in, but several years ago when I had to replace a nozzle flange meeting the description you provided (flange welded to a pipe nozzle and not the pressure membrane of the vessel itself), the mechanical engineers told me it was part of the vessel and required a code weld, repair stamp, all that stuff. What an effort that was when a pipefitter/welder was objectively capable of doing the job just like he could if it were any other pipe weld.

I'm not sure there is such a paragraph. The designer establishes the boundaries of the vessel but as far as the code is concerned, the last weld to the vessel ( shell, head nozzle etc) is the only weld that is required to be considered a vessel weld.

That is to say, for any nozzel that is welded to what is considered a part of the vessel itself, that weld is a code weld. Anything beyond that, a flange for instance welded to the nozzle end, is not code unless the manufacturer designates it as a vessel weld by describing it on the Data Report.

Therefore, if you put the flange on the data report, YOU have made it a part of the vessel and you're stuck with that decision once the vessel has been hydro tested and stamped. If the vessel is not complete and has not stamped or inspected you can write a deviation, make an engineering change or replace the flange. If you describe the vessel as having, for instance a 2" sch 40 nozzle and do not describe it as flanged, even though you have put a flange on the nozzle for hydro testing, you may cut it off and replace it even if the vessel is complete and stamped.

If, on the other hand, you have an "R" stamp, have described the nozzle as having a flange on your Data Report you can change the flange and make it a repair under your "R" stamp.

Thank you Morgan 23. I think you've clarified the situation.

Cloaked in darkness and feeling an alien presence I turned on the light. There he was, my arch-nemesis, staring back from the mirror.