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
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)