Quick reference
The formulas, limits and codes behind the FEXLA calculators, on one page. Each links to the note that explains it.
Formulas
| What | Formula | Note |
|---|---|---|
| Hoop stress, thin cylinder | σθ = PD / 2t | D diameter, t wall thickness |
| Longitudinal stress | σx = PD / 4t | Half the hoop stress |
| Shell thickness, ASME VIII-1 UG-27 | t = PR / (SE − 0.6P) | Valid for t ≤ R/2 and P ≤ 0.385SE; S allowable, E joint efficiency |
| Local stress at an attachment | σ = Kn·N/T ± Kb·6M/T² | N force and M moment per unit length; Kn, Kb optional stress concentration factors |
| Decay length | λ = √(Rm·T) | Local bending dies out over about this length |
Where these come from: attachment method notes
Stress categories and limits
| Category | Meaning | Limit |
|---|---|---|
| Pm | General primary membrane, away from the attachment | S |
| PL | Local primary membrane at the attachment | 1.5S |
| PL + Pb + Q | Primary plus secondary, checked together | 3S |
| F | Peak, at the weld toe | Fatigue only; a shell model does not resolve it |
Which standard, for which module
| FEXLA module | Checks | Standards | Notes |
|---|---|---|---|
| Junctra | Attachment analysis | WRC 537 (and 107); ASME VIII-2 Part 5 | Read |
| Liftrix | Rigging and lugs | Moss procedures 10-3 to 10-8; ASME BTH-1; ASME B30.26 | Read |
| Plenara | API 661 air-cooler headers | ASME VIII-1 Appendix 13, UG-34 | Read |
| Corix | Specialty analyses | ASME VIII-2 4.5.17.3, 5.2.3 and 5.4.2 | Read |
| Pipe Atlas | Pipe, flange, fitting and gasket tables | ASME B36.10M, B36.19M, B16.5, B16.47, B16.9, B16.20, B16.21 | Open |
A summary for orientation, not a substitute for the code. Check the current edition of each standard before design use. The finite-element modules are in early access and under independent verification.