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ASME B31.3 is an internationally used code for process piping, particularly in the chemical and petrochemical industries.
ASME B31.3 is titled “Process Piping” and forms part of the ASME Code for Pressure Piping, B31. It applies to piping in refineries, chemical and pharmaceutical plants, the paper and semiconductor industries, cryogenic plants and related processing facilities. Power plant piping has its own code, ASME B31.1.
The code covers the whole life of a pipe up to commissioning: materials, design, fabrication, assembly, erection, examination and testing.
ASME B31.3 distinguishes piping by the fluid and its operating conditions, the fluid service. Material selection, permitted components and the extent of examination depend on this classification. It is not made by the designer: the code assigns it to the owner.
Anyone drawing up a piping class to ASME B31.3 therefore needs this decision first – it comes before any calculation.
The wall thickness of straight pipe follows from the pressure design equation of the code; allowable stresses are tabulated in Appendix A. Pressure and weight are the sustained loads: their longitudinal stress S_L must not exceed the allowable stress at operating temperature, S_h.
Thermal expansion is assessed separately. What governs is the displacement stress range S_E between operating conditions; it is limited to S_A = f · (1.25 · S_c + 0.25 · S_h), where S_c is the allowable stress in the cold condition and f a factor that drops below 1 for high numbers of cycles. For occasional loads such as wind or earthquake, the code permits 1.33 times S_h together with the sustained loads.
The extent of non-destructive examination depends on the fluid service. Before start-up the piping is leak tested under pressure: as a hydrostatic test at not less than 1.5 times the design pressure, adjusted by the ratio of allowable stresses at test and design temperature, or – with special safety precautions – as a pneumatic test at 1.1 times the design pressure.
Within the European Union, pressure equipment falls under the Pressure Equipment Directive 2014/68/EU. ASME B31.3 is not a harmonised standard; designing to it does not automatically give a presumption of conformity. It can be used, but the manufacturer must additionally demonstrate that the essential safety requirements of the directive are met – for example regarding materials, test pressure and conformity assessment.
The code is reissued at regular intervals. The edition that applies is the one agreed in the contract.
What Entracon offers here is on the matching page.
See what we offer| Category | Characteristic | Consequence |
|---|---|---|
| Category D | Non-hazardous fluid at low pressure and moderate temperature | Relaxed requirements for components and examination |
| Normal Fluid Service | Everything not assigned to another category | Standard requirements of the code |
| Category M | Fluid where even a very small leak can cause serious, irreversible harm to people | Stricter requirements for components and examination |
| High Pressure | High-pressure range designated by the owner | Separate chapter with its own design rules |
ASME B31.1 covers power piping, ASME B31.3 process plants. Both belong to the same code family but differ in allowable stresses, factors and extent of examination. Results cannot be carried over from one to the other.
Yes, provided compliance with the essential safety requirements of the Pressure Equipment Directive is demonstrated in addition. The code alone gives no presumption of conformity; the gaps to the directive have to be closed one by one.
Within a plant, yes; within one piping system, no. A design is carried out entirely to one code – with its material values, factors and examination rules.
The owner. The owner knows the fluid, the mode of operation and the hazard; the designer turns the classification into a piping class and an examination scope.
One short conversation usually settles more than three quotations. Call or write — you will reach an engineer directly.
Start typing – for example “balancer”, “SAP” or “pipe stress”.
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