Non-metallic Pipe

Written by Matt Milbury on . Posted in Pipe

There are several advantages and limitations between using metallic or nonmetallic materials instead of using steel piping.

Advantages

  • Typically has a lower installed cost and lower total cost of ownership.
  • Will not corrode if the correct material is selected. This means:
    • No cathodic protection or corrosion monitoring
    • No chemical inhibitors are required.
    • Corrosion allowance is avoided (Note: if the service is an erosive service, an erosion allowance may be required)
  • Flow properties are superior to steel pipe
    • Lower pumping costs
    • Consistent friction factor through the life of the pipe
  • More flexible than steel pipe. This allows for some nonmetallic piping to be ordered in spools that are hundreds of feet long.

Disadvantages

  • Temperature limits are usually lower than steel pipe. As temperatures increase, the maximum pressure will decrease.
  • Maximum pressure is lower than steel pipe.
  • Material is very process dependent. That is, hydrocarbons cannot always flow through nonmetallic lines.
  • Non metallic lines will degrade in sunlight without a Ultraviolet inhibitor.
  • Very susceptible to mechanical damage.
  • More flexible than steel pipe. Requires more supporting than steel piping.

Standards

  • ASME Standards

Not all non-metallic piping can be used in all services. For example:

  • ASME B31.3 - Process Piping
    • Thermoplastics cannot be used when the service is a flammable service and when the piping is above ground. Thermoplastics also must be safeguarded when in all services (except in Category D fluids). While safeguarding is not defined, it could mean that additional pressure & temperature protection is required. It could also mean that physical barriers be installed to prevent unintentional rupture.
    • Thermosets can be installed if they are safeguarded when the service is flammable or toxic.
  • ASME B31.4 - Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids does not allow thermoplastics.
  • ASME B31.8 - Gas Transmission and Distribution Piping Systems allows for nonmetallic piping at low pressures (<100psi)