Local stress analysis for pressure vessel nozzles, lugs and supports. FEXLA is a set of tools for pressure vessel engineers: each one checks one kind of job, shows its working, and gives you a report you can file.
Under FEXLA
Free during early accessComplex tools, by invitation
What you can use today
Pipe, flange, fitting and gasket dimensions from the standard tables, with pressure ratings. Open it and look things up.
Open Pipe AtlasLocal stress where a nozzle or clip is welded to a shell. Every coefficient is shown, so a reviewer can follow the number.
Open the calculatorCheck a lifting lug, a trunnion or a tailing lug for a vertical or a horizontal vessel: the lug, its weld, the shackle, the shell under it, and a report with a checklist.
Open the lug calculatorWhere the standard method stops, the same case opens as a model of the shell. Priced separately, and open to invited engineers while we verify the results.
Ask about accessTry it
This runs the same WRC 537 calculation as the calculator, in your browser. Change a number and the checks move.
Result
PASS
WRC 537 local stress at the nozzle and pad edges, against the ASME VIII-2 limits. 2 engine notes are in the full report. A quick check, not a design record.
The report
Every check ends in a report that shows its working, so the next engineer can check it without asking you. Slide through a sample.
Sample report, page 1 of 6. Invented data, to show the layout of a report. Not a real vessel.
Nozzle N3 on shell V-101
Local stress at a round nozzle with a reinforcing pad, by WRC 537.
Result
PASS
All checks are within their limits. The highest ratio is 0.45, local primary membrane stress at the nozzle edge.
| Method | WRC Bulletin 537 |
| Acceptance | ASME VIII-2 Part 5 limits |
| Units | SI (mm, MPa, N) |
| Material, shell and pad | SA-516 Gr 70 |
| Shell inside diameter | 1800 mm |
| Shell thickness | 22 mm |
| Corrosion allowance | 3 mm |
| Allowable stress, S | 138 MPa |
| Design pressure | 1.2 MPa |
| Design temperature | 150 °C |
| Nozzle outside diameter | 273.1 mm |
| Nozzle wall thickness | 12.7 mm |
| Pad outside diameter | 420 mm |
| Pad thickness | 16 mm |
External loads at the junction
| Radial load, P | 2000 N |
| Shear, VL and VC | 1500 N, 1500 N |
| Moments, ML, MC, MT | 2, 1.5, 1 kN·m |
The bulletin works from the shell mean radius, the thickness at the nozzle edge and the size of the attachment.
Pressure stress in the shell: hoop 57.03 MPa, longitudinal 28.52 MPa.
MPa. A to D are the four points round the nozzle; u is the outer surface, L the inner.
| Point | σφ | σx | τ | Combined |
|---|---|---|---|---|
| A outer | 85.3 | 20.6 | 0.36 | 85.3 |
| A inner | 94.7 | 35.0 | 0.36 | 94.7 |
| B outer | 95.9 | 33.6 | 0.15 | 96.0 |
| B inner | 89.9 | 24.1 | 0.15 | 89.9 |
| C outer | 49.3 | 40.9 | 0.15 | 49.3 |
| C inner | 63.6 | 49.2 | 0.15 | 63.6 |
| D outer | 62.0 | 48.6 | 0.36 | 62.0 |
| D inner | 52.4 | 43.6 | 0.36 | 52.5 |
Highest combined stress 95.95 MPa at point B, outer surface. The pad edge is lower, at 67.7 MPa.
After Run Analysis the calculator draws the case to scale: the shell, the nozzle in green and the loads where they act. The same figure is placed in the report. This one is an example from the calculator, not this sample case.
Where it applies
Wherever something is welded to a shell and its load has to go into the wall.
FEXLA model
FEXLA model
Learn
Written from what the programs actually compute, with the equations and a worked number.
Questions
Checking the local stress where something is welded to a pressure vessel: nozzles and clips by WRC 537 and by a finite-element shell model, lifting and tailing lugs, agitator nozzles, skirt openings and API 661 air-cooler headers to ASME VIII-1 Appendix 13.
The WRC 537 calculator is complete and shows every coefficient and code paragraph. The finite-element modules are in early access for invited engineers and are under independent verification; until that is finished their results are not a source of design values.
WRC Bulletin 537, ASME VIII-1 (UG-27 and Appendix 13), ASME VIII-2 Part 5 (stress categories, 5.2.3 limit-load, 5.4.2 buckling, 4.5.17.3), Moss procedures 10-3 to 10-8, and ASME BTH-1 and B30.26 for lifting lugs.
No. Shell thickness and opening reinforcement for pressure are sized in your vessel program. FEXLA checks what is attached to the shell and the loads it brings.
On a cylinder: a round nozzle, radial or hillside, or a rectangular clip. On a cone: a round nozzle. On a formed head: a round nozzle in the spherical region. A reinforcing pad is optional on each.
Yes. Rectangular clips and the brackets that carry platforms, pipe supports and ladders are checked with the clip calculator, by WRC 537. Structural sections and clips close to a seam or another attachment go to the finite-element shell model.
Yes. It steps the lift through its angles, finds the load at each lug, checks the plate to Moss and AISC and to BTH-1, checks the shackle fit, and then builds a shell model of the governing lug. Trunnions, a tail beam and two offset lugs are covered; a base ring is checked by hand.
Yes. A nozzle on a top head carrying an agitator, under its weight, thrust, torque and rotating bending moment, with the fatigue cycles worked out from speed, running hours and the number of starts.
Yes, plug headers and welded rectangular boxes to ASME VIII-1 Appendix 13: the stress at each location, the tube-hole ligaments, end plates and stays, the required thickness, the MAWP and the test condition. Nozzle and support loads on the header are not covered; check a header nozzle as an attachment.
Yes. A tombstone, obround or round access opening in a support skirt, with its sleeve and an optional pad, under weight and wind or seismic moment, with the ASME VIII-2 4.5.17.3 hand checks beside the shell model. The base ring, gussets and anchor chairs are not modelled.
All six components of the bulletin: a radial load, two shear forces, two bending moments and a torsional moment. You can give them at the shell junction or at the end of the nozzle, and the calculator carries them to the junction. Pressure is added to the local stresses.
When the bulletin stops: a case outside its charted range, an attachment close to a head, a cone junction, a seam or another attachment, a large opening for the shell, a tilted or tangential nozzle, an obround opening, or stresses wanted in the nozzle or the pad. The calculator tells you when a case falls outside the bulletin and offers to carry it across.
Eigenvalue buckling to VIII-2 5.4.2 and an elastic-perfectly plastic limit-load check to 5.2.3. Large-displacement analysis, local strain limits and elastic-plastic ratcheting are not done yet.
A list of common ASME II-D materials with the allowable stress taken at your design temperature, or your own material and allowable stress. Metric and U.S. units both work, and you can switch between them.
The stresses at every evaluation point, the pass or fail against 1.5S and 3S, a 3D model of the case and a calculation report. You can save the case to your history and download the report as a PDF.
Yes. Pipe Atlas, with ASME B36.10M and B36.19M pipe, B16.5 and B16.47 flanges, B16.9 fittings, ratings and gaskets, needs no sign-in.
Pipe Atlas is free and needs no sign-in. The WRC 537 calculator and the lifting and tailing lug calculator are free during early access, and every new account is reviewed before it is opened. The finite-element tools are not free: they are priced separately and open to invited engineers, so ask us about access.
The WRC 537 calculator, the lifting and tailing lug calculator and Pipe Atlas are free during early access. The finite-element tools are not free.
WRC 537 calculator, lifting and tailing lug calculator, Pipe Atlas and your own history. Every new account is reviewed before it is opened.
Free during early access
Request accessLugs, headers, agitators, skirts, buckling and limit-load. Early access, for invited engineers.
Priced separately
Ask about access
Local stress at nozzles and clips, lifting and tailing lugs, skirt openings, air-cooler headers. Enter the vessel and the loads; the stresses, the pass or fail and a report ready for the file come back together.