minimum nozzle length

[DaveMECHeng]

I am trying to determine the minimum nozzle length per ASME BPVC Section X for an FRP nozzle to shell attachment.

RD-620.1 states a minimum length of 6 inches unless otherwise stated in Procedure specification and Design Report.
Using the ASME design calculations for minimum nozzle length, RD-1174.2 Lb (overlay length) requires a minimum 3 inches.
Table RD-620.1 requires L=4FT, length is 4 times thickness of flange.

Due to nature of the item we want to make nozzle lengths just a few inches from the shell, and violate the above mentioned minimum lengths. This is accomplished by trimming down the nozzle. It seems to me the shorter length would be better (less moment arm). Do I have to follow RD-1174.2 and Table RD-620.1 to maintain minimum length of nozzle? The reason I ask is the above mentioned calculated lengths are for the minimum overlay length. I'm looking for some ASME legal language to justify my decision.

Thanks in advance

 

[pennpiper]

Have you considered:
- Bolt removal?
- Wrench clearance?
- Gloved Hand and finger clearance?
- Insulation (if any) clearance?
- How the FRP Nozzle is created in the first place?
- Structural integrity of the finished Nozzle?
- Why the rush to such a short Nozzle Projection?

Sometimes its possible to do all the right things and still get bad results

 

[racookpe1978]

Perversely, the long FRP nozzle length is more important that the same "nozzle length" is for a fillet welded steel nozzle.

The steel is welded with a fillet around the circumference of the pipe, right?

The FRP needs room to wrap and smooth down and layer-up the MANY layers of impregnated plastic wrapping around the primary nozzle shape and the exterior wall and face of the vessel.

So you need room for hands and gloves (as above) during wrapping and fabrication, and for the bolts to attach the future next assembly during assembly, but for the grip area of the wrapped plastic belts to overlap each other, overlap the vessel face, and to wrap around the nozzle itself.

 

[DaveMECHeng]

Thanks for the replies. The current design is being constructed and passes hydrostatic testing. We are trying to certify it for AMSE approval. It is physically possible for us to construct.