Hello,

I have a problem where a small elbow of pipe near a termination point fails due to thermal expansion and an over constrained pipe. I read up on nozzle flexibility however my process unit is nor suitable as the OD is too small for the relevant code.

Does anyone know of alternative methods for including nozzle flexibility as there is no room for an expansion loop in this section of pipe.

The "CODE" is a guideline especially for flexibility issues. Engineers can use "more applicable data" or alternate calculations as long as the technique is sound and can be documented. Just remember to always get the PRIMARY (SUS) design right. Provide a sketch and/or the OD and T of the items involved to illicit more advice.

Insufficient information. Manners of calculating flexibility of nozzles will vary based on what the nozzle is attached to.

Norton,

Suggestion: Try to employ an overall view of the Piping + Vessel + Steelwork System.

My understanding is you have over-stress issue on PIPING system (pipe spool and/or pipe elbow).

You say: "...my process unit is nor suitable as the OD is too small for the relevant code.".
This is definitely an unclear statement. Probably, by "Process Unit" you mean equipment/vessel, and "a too small OD" would mean that (OD)nozzle/(OD)vessel ratio is too high to yield to a relevant (read "low enough") stiffness of the "nozzle-shell" junction.
Have you tried to compute the stiffnesses by Finite Element Analysis (FEA), or you've used only Caesar II Built-in WRC297 Module? FEA approach is much more realistic and would provide realistic stiffness values.

Anyway, even if "nozzle-shell" junction stiffness is relatively high, you may approximate the actual stiffnesses of the pipe supports and/or of the terminal anchors (e.g. realistic boundary conditions). Please remember that pipe supports' actual stiffnesses are significantly lower than 10^12 order magnitude assumed by Caesar II software.

Finally, if your thermal expansion over-stress is not very high (i.e. less than 20%), you may use a realistic Fatigue Stress Reduction Factor "f" (e.g. f = 1.00 ... 1.20) to increase the Allowable Displacement Stress Range SA, according to ASME B31.3 provisions. Such approach may be employed, based on sound engineering judgement, if Loading-Unloading Thermal Cycles for the System Design Lifetime is lower than 7000.

To conclude, there are not "magic" formulas or "wizard" approaches to make a Piping-Vessel System to match Code compliance requirements. It's just a matter of Code requirements knowledge and sound engineering judgement.

If you are dealing with a newly-designed System, and you encounter such flexibility-lack problem, definitely RE-DESIGN is required. Either an expansion loop or an expansion joint...

Regards,