B31.3 Nozzle Calculations through B16.9 Pipe Cap

[kjf1]

I am doing a design which requires a 3" Sch 40 nozzle to extend through (along the axis)of an 8" Sch 40 B16.9 Pipe Cap. I understand the branch calculations in B31.3 for run pipe, but how do I apply them to a pipe cap? Also, I want to install a 1/4" coupling as a drain in the pipe cap beside the 3" pipe. How do I calculate that, and how close can I place the drain to the 3" pipe.

 

Hello,

I would encourage you to remove the cap and use reducers to get the result you are trying to attain.

Since I will assime you will not do that, I would encourage you to very closely study B31.3, Paragraph 304.4.2, "Openings in Closures", as well as that paragraph's references to the ASME B&PV Code. The drain should be placed on the NPS 8 pipe - it would be bad practice to do otherwise. However, if the coupling is installed in the cap, it should be outside the "reinforcing zone" around the opening made for the NPS 3 pipe.

There are complications when making openings in B16.9 fittings that may not be apparent. The fittings are subjected to stresses other than the circumferential stresses that pipe (cylinder) wall thickness minimums are designed for. That is to say the cap may need more thickness than the pipe for a given pressure. So when applying the area replacement rules the MEASURED thickness of the cap (it is not a "standardized dimension in B16.9) should be used to calculate the amount of metal area (if any) that needs to be replaced.

Best regards, John.

 

[ralphsare]

suggestion.
remove the cap and install a weld neck flange and blind (you'll have to figure out the rating and im assuming its not 600# either and the matl is not exotic). drill the blind and stick a 3nps weldolet where u connect your 3 nps spool.

if youre worried that the hole may reduce the flange rating, u may caheck out the stress using the roark handbook (donut plate).

 

[reichertc]

Always fun trying to modify a fitting, because you have no idea what the manufacturer is actually going to send you. Up here in Canada, we have something called a CRN, which stands for "Canadian Registration Number". In general, all fittings used in piping systems in Canada require a CRN. To get a CRN, manufacturers need to provide the regulatory authorities with either detailed calculations showing the fitting is "strong" enough (ie. FEA), or they have to perform a proof test. A fitting that is modified will require a new CRN. Esentially, we need to comply with ASME B31.3 Para 304.7.2 for unlisted fittings. If you absolutely need to build this the way you describe, either do the FEA or the proof test.

The advantage of the FEA is that you can take actual wall thickness and geometry measurements to perform the calculations. The proof test may be easier, but you will need to locate a cap with the same fabrication dimensions(preferably from the same manufacturer) in order to perform the test.

 

[ralphsare]

the mods is being done at the user facility not by the fitting manufacturer, so crn dont apply. the end user is prepared to qualify it thrugh calc (not necessarily a fea) then it presupposes that quality inspection is going to beperformned hence a hydro would had been part of the exercise (weld are of course to meeting asme reqt). normally a 2inch hole does not impact much on the strenght reduction of the pressure cylinder (self reinforcing i guess was the term used by asme user) so a 3in hole on a 8in thick flange using a rated component wont present much complication. the very act that a qualification is being planned prior to implementation speaks of the attitude of the palnt personnel toward ensuring that changes are done tocomply with code reqt. fea and proof test in this instance is a bit of an overkill. API has recognize that piping in their life is subject to alteration and reduction in strenght and has published Piping Nspection Code. Will one perform a proof test everytime a change, alteration, repaired or rearating has to be performaned for piping already in-service? i very much doubt it. it has a big impact not only in the way business is being managed but possibly increases the exposure of plant personnel to risk.