O-lets in ASME VIII wall thickness calculation! 1

[gbratis]

Hi folks,
Here's a quicky for you pressure vessel guys!!!.
Is there any reference in the ASME VIII div.1 that states that the use of o-lets as nozzles does not require any reinforcement calculation. For example in a high pressure vessel with a design pressure of 70 Barg shell OD 24" there is a 4" opening for which a weldoflange is used. Instead of using this configuration a did my calcs using a typical 4" pipe-nozzle(set-in same schedule) that led to the conclusion that a reinforcing pad is mandatory.Why this ambiguity?
Thanks in advance!!!

 

[johnnymist2003]

Hi gbratis,
1) No, ASME does not exempt reinforcement calculations for o-let nozzles, except if they fall into the exemption categories as specified in UG-36 (c)(3).
2) In my experience, the weldoflanges, etc. are normally forged. Did you use the allowable stress values for the forging material of the weldoflange vs a pipe material ?
3) From the ones that I have seen, the weldoflanges typically have a thicker section at the base where they attach on to the vessel. This would mean that the pipe schedule would not be applicable because some (maybe all, depending on the reinforcement limits) of this thicker section on the weldoflange could be used as reinforcement.This would mean that effectively the area in your pipe neck within reinforcing limits could be much smaller than the weldoflange arrangement. This could necessitate that for the pipe neck, a reinforcing pad is required, as your calculations pointed out.
4) If you have problems with reinforcing using the pipe (which is a more conservative approach), then I'd recommend that you use the actual weldoflange dimensions. This, in itself, may be a problem unless you can get the dimensions from the manufacturer, as typically the dimensions of the thickened section at the base are not given in the catalogs.
5) You could use another alternative, possibly a long weld neck flange, in lieu of the weldoflange. In my experience the use of long weld necks normally negates the requirement for the fitment of a pad, again, because the long weld necks are thicker than the pipe schedules, and are forged.
Hope this helps.

 

[twistobar]

Take a look at UG-11 of ASME VIII-1 (A05).
It allows, under certain conditions, the use of standard parts having a Manufacturer's standard pressure-temperature rating.
Follow this link to get to the Manufactuter's Standard:

http://www.bonneyforge.com/OletCat.PDF

Hope it helps.

... a man's got to do what a man's got to do...

 

[GenB]

eld'olets and thread'olets are qualified and are called self reinforcing,
qualification as the required ASME ANSI std is required
per the pressure and temp design.
genb