Most rejected vessel packages fail on the same handful of UG-37 details. Here is what reviewers look for first.
Why nozzle details decide the review
Shell and head thickness calculations are usually correct, because they are simple and everybody checks them. Nozzle reinforcement is where assumptions accumulate: corrosion allowance handling, limits of reinforcement, weld strength paths and material substitution all interact, and a single wrong input changes whether a repad is needed at all.
When a fabricator's package is rejected late, the cost is rarely the calculation. It is the plate already cut, the sequence already planned and the schedule already committed.
The five recurring errors
Across design reviews in Malaysian and regional fabrication yards, the same issues appear again and again:
- Corrosion allowance omitted from the nozzle neck while it is applied to the shell
- Limits of reinforcement taken beyond what UG-40 permits, so available area is overstated
- Reinforcement area credited from weld metal without checking weld strength paths
- Nozzle in a head treated as a nozzle in a shell, with the wrong required thickness basis
- Material substitution accepted without re-checking allowable stress at design temperature
A practical review sequence
Work the calculation in the order a reviewer will: confirm the design basis and corrosion allowance, recompute required thickness at the opening, establish the limits of reinforcement, then total available area and only then decide on a repad. Document each input with its source — that is what makes the package defensible in front of a third-party inspector or DOSH.