Nozzle Reinforcement to counteract Pipe Loads
Nozzle Reinforcement to counteract Pipe Loads
(OP)
I have a vessel which, due to location and service has very high nozzle loadings, particluarly moment loading, presenting problems with allowable stresses being exceeded.
We are limited in the space available to include repads and do not want to increase the shell/nozzle thicknesses - I understand that webs betwen the shell & nozzle can be used to isolate the bending moments but ASME VIII Para UG37 only covers pad reinforcment - how can the stresses be calculated and proven?





RE: Nozzle Reinforcement to counteract Pipe Loads
I presume you have performed a Pipe stress analysis on the attached piping to come up with the nozzle loads? If so was the shell flexibility of the vessel included in the analysis. If not then this could reduce the actual loads significantly.
RE: Nozzle Reinforcement to counteract Pipe Loads
I really support DSB123, The shell flexibility of the vessel should be included in the pipe stress analysis.
However, the best solution for your problem is to reduce the nozzle loading by implement some modification on the piping system itself not to increase the shell / nozzle thickness or to reinforce the nozzle.
RE: Nozzle Reinforcement to counteract Pipe Loads
The old WRC 107 method (Bijlaard), which is incorporated in various computer programs such as CAESAR and CodeCalc.
FEA from scratch.
FEA using programs such as FEPipe that incorporate automatic mesh generation.
Other methods, such as the simplified approach provided in Bednar's book, Pressure Vessel Design Handbook.
Don't forget to include the pressure thrust load as part of the loads acting on the nozzle.
RE: Nozzle Reinforcement to counteract Pipe Loads
Part of the issue is a relatively large diameter, yet short length of pipe, giving a limited degree of flexibility. It appears that this will have to be modified.
My main questions was as to whether webs can be used in place of, or additional to, repads to compensate, aleviate or distribute stresses due to nozzle moment loads. FEA would provide a perfect analysis, but can the effects of the web be calculated by hand in a similar method to the pressure area method for pressure reinforcement be used (as outlined in UG37)?
My suspicions are that they cannot, as the load is still applied to the shell and if present, reinforcement, which must still be thick enough to hold the load.
RE: Nozzle Reinforcement to counteract Pipe Loads
I concur with other responders: if you can't really take those loads with a repad, you should have either the piping modified or a more in depth analysis made.
prex
http://www.xcalcs.com
Online tools for structural design
RE: Nozzle Reinforcement to counteract Pipe Loads
Steve Braune
Tank Industry Consultants
www.tankindustry.com
RE: Nozzle Reinforcement to counteract Pipe Loads
The problem is always a bit of chicken and egg - since your customer doesn't have details on the shell flexibility to start with, he has to assume a rigid connection, which in turn leads to larger anchor loads.
Edward L. Klein
Pipe Stress Engineer
Houston, Texas
"All the world is a Spring"
All opinions expressed here are my own and not my company's.
RE: Nozzle Reinforcement to counteract Pipe Loads
If you have the opportunity to modify the vessel nozzle, a thicker "nozzle reinforced" connection with a full pen weld and appropirate vessel membrane flexibility may indicate teh existing piping and supports are OK.