Fluid Service

Written by Matt Milbury. Posted in American Society of Mechanical Engineers

B31.1 Fluid Services

Applies to all fluids where steam vapor is generated at 15 psig or higher. Steam condensate (liquids) where water is 160 psig or temperatures exceed 250F.

B31.3 Fluid Services

Category D Fluid Service

  • Fluid is not flammable, not toxic or otherwise harmful to human tissues. Harmful means exposure that can harm skin, eyes or mucous membranes that irreversible damage may result unless immediate action is taken.
  • Design Gauge pressure is below 150 psi (1,035 kPa)
  • Design Temperature is between -20F to 366F (-29C to 186C)

An example of Category D fluid might be utility water in a plant or low pressure steam condensate.

Category M Fluid Service

Category M service is a fluid where the potential for personnel exposure is considered to be significant and where a single exposure to a very small amount can cause serious irreversible harm to people. This could be death, respiratory failure, blindness, etc. Design for Category M Fluid service should also meet the requirements of Chapter VIII of B31.3.

An example of Category M fluid could be Hydrogen Sulfide gas, high concentrations of HydroChloric Acid or high pressure steam.

High Pressure Fluid Service

High Pressure Fluid Service is one the pressures are in excess of ANSI Class 2500. It is important to note that B31.3 notes that there are no specified pressure limitations for the application of the High Pressure Piping Rules. Design for High Pressure Fluid service should also meet the requirements of Chapter IX of B31.3.

Normal Fluid Service

Fluid service that is covered by 31.3 but not subject to the rules for Category D, Category M or High Pressure Fluid definitions.