The fluid transported in the pipeline should be categorised in one of the following four groups, depending on its hazard potential:
1. Category A: Non-flammable, stable and non-toxic fluids which are liquid at prevailing ambient temperature and atmospheric pressure plus 0.5 bar, i.e. the vapour pressure is lower than 1.5 bar (abs) at ambient Example: water, slurries.
2. Category B: Flammable, or unstable or toxic fluids which are liquid at prevailing ambient temperature and atmospheric pressure plus 0.5 bar, i.e. the vapour pressure is lower than 1.5 bar (abs) at ambient Example: stabilised crude, gasoil.
3. Category C: Non-flammable, stable and non-toxic fluids which are gases or a mixture of gas and liquid at prevailing ambient temperature and atmospheric pressure plus 0.5 bar, i.e. the vapour pressure is higher than 1.5 bar (abs) at ambient temperature. Example: nitrogen, carbon dioxide.
4. Category D: Flammable, or unstable or toxic fluids which are gases or a mixture of gas and liquid at prevailing ambient temperature and atmospheric pressure plus 0.5 bar, i.e. the vapour pressure is higher than 1.5 bar (abs) at ambient temperature. Example: natural gas, liquid petroleum gas, ammonia.
Pipelines carrying category A and B fluids should be designed and constructed in accordance with ANSI/ASME B31.4.
Pipelines carrying category C and D fluids should be designed and constructed in accordance with ANSI/ASME B31.8.
NOTE: Liquid petroleum gas and anhydrous ammonia, which are covered by ANSI/ASME B31.4, fall under category D. Pipelines transporting these products therefore should be designed to ANSI/ASME B31.8.
