Non-metallic Pipe

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

 

Non-metallic Pipe 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.

 

Non-metallic Pipe 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.

 

Non-metallic Pipe 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)