Services · 03
Piping and fittings, calculated — and analysed where the code requires it.
We have developed our own Excel sheets for mechanical calculations on commonly used piping codes, and carry out flexibility and stress analysis in industry-trusted software where it governs.
The B31 series
Four codes, four different sets of rules
| ASME B31.1 | ASME B31.3 | ASME B31.5 | ASME B31.12 | |
|---|---|---|---|---|
| Application | Boiler external piping | Refineries, chemical, pharmaceutical, pulp and paper, semiconductor, cryogenic | Refrigeration and secondary coolant systems | Hydrogen piping and pipelines |
| Basic allowable | lesser of UTS/3.5 and 2/3 × Yield | lesser of UTS/3.0 and 2/3 × Yield | as B31.3 basis | B31.3 basis, reduced by a material performance factor |
| Service grading | None — single service | Category D, Normal, Category M, High Pressure, High Purity | Refrigerant service | Part IP industrial piping · Part PL pipelines |
| Examination | Largely fixed by pressure and temperature | Scales with fluid category — from spot checks to 100% | Prescriptive for refrigerant joints | More stringent than B31.3 throughout |
| Design responsibility | Operating company | Explicitly assigned to the Owner | Owner and installer | Owner |
Non-standard fittings
Designed to ASME code
Standard-compliant fittings are the straightforward case. Fittings such as valves, measurement devices — thermowells, Coriolis meters and various flow meters — Y strainers, sight glasses and expansion joints can be designed to the B31.3 or B31.1 code. We have developed Excel sheets and also use numerical methods to evaluate non-standard fittings, and can provide pressure–temperature ratings for your non-standard fitting catalogue — the basis of a Fitting CRN.
Why it is required
Pipe stress analysis
ASME B31.3 does not demand formal analysis of every system. Para. 319.4.1 exempts a system that duplicates or replaces without significant change a system with a successful service record, that can readily be judged adequate by comparison with previously analysed systems, or that is of uniform size, has no more than two points of fixation, no intermediate restraints, and falls within the limits of the empirical equation given in para. 319.4.
Anything outside those three cases requires formal analysis. In practice that captures most real systems — anything with intermediate supports, changing diameter, more than two anchors, or connections to sensitive equipment. The Code itself cautions that no general proof exists that the empirical equation always produces accurate or conservative results.
Where the analysis earns its keep
- Equipment nozzle loads
- Rotating equipment and air-cooled exchangers have tight allowables, and exceeding them causes misalignment and seal failure rather than pipe failure — the most common reason a system fails analysis.
- Flange leakage
- Joints that pass a stress check can still separate under combined moment and thermal load.
- Support and structure loads
- The analysis produces the reactions the structural design needs — without them, supports are sized by assumption.
- Spring hanger selection
- Sizing and travel for systems with significant vertical thermal movement.
- Skids and spools
- Compact routing produces stiff systems with little natural flexibility, so thermal growth has nowhere to go.
- High-temperature service
- Thermal expansion, creep range behaviour and cold spring where specified.
- Occasional loads
- Wind, seismic, relief valve reaction, water hammer and slug flow.
- Buried and jacketed piping
- Soil restraint or the jacket changes the restraint condition entirely.
- Troubleshooting
- Investigating vibration, support failures or cracking in systems already in service.