The short answer is: generally, no, plastic gas pipes are not permitted to be used unprotected above ground for natural gas or propane distribution due to significant safety concerns and regulatory restrictions. While plastic, specifically polyethylene (PE) or sometimes specialized PVC, is the preferred material for buried gas lines because of its corrosion resistance, its vulnerability to mechanical damage, fire, and ultraviolet (UV) degradation makes it unsafe for exposed applications. In most jurisdictions and codes, plastic is limited to underground installation, with specific provisions for transitioning back to metal at the surface.
Regulatory Prohibition and the Need for Protection
Most international and national fuel gas codes, such as those referenced in the NFPA (National Fire Protection Association), explicitly state that plastic pipe must be installed underground only. The primary reason is physical protection. Above-ground plastic pipe is highly susceptible to external rupture from vehicles, tools, and everyday impacts. If an above-ground pipe were to break, it would immediately release flammable gas, creating an explosive hazard. Therefore, any portion of a plastic gas line that must rise above grade, such as a connection point, is typically required to transition to a metallic pipe, like steel, or be enclosed in a protective metal conduit or anodeless riser.
Why PVC is Unsuitable for Gas Lines
The common plastic known as PVC (Polyvinyl Chloride), which is often used for non-pressurized drainage and in specialized agricultural systems like irrigation piping, is typically prohibited for conveying fuel gas altogether in many codes. While specialized high-impact PVC (PVC-HI) has been used in some older, low-pressure gas grids overseas, standard PVC pipe and PVC pipe fittings are considered unsuitable for high-pressure gas service due to several factors:
Low Heat Distortion: PVC softens at relatively low temperatures, posing a fire risk.
UV Degradation: PVC, like most plastics, degrades quickly when exposed to direct sunlight, leading to embrittlement and cracking.
Low Pressure Limits: PVC is typically limited to low-pressure applications, far below the requirements for most residential and commercial gas transport.
For safety, installers must avoid using water-grade PVC pipe and PVC pipe fittings for gas service under all circumstances.
The Problem of UV Exposure in Plastic Pipes
Even polyethylene (PE) pipes, which are the standard for underground gas distribution, face issues when exposed to sunlight. Polyethylene is susceptible to degradation from UV radiation, which causes photo-oxidation, leading to surface cracking and embrittlement over time. Manufacturers mitigate this risk by incorporating carbon black (usually 2.0% to 2.5%) into the plastic compound, which acts as a UV shield. While black PE pipe is more UV-resistant than white PVC, codes still prohibit its long-term use in exposed gas applications where failure could be catastrophic. The connection points and specialized PVC pipe fittings used in similar plastic systems must also be rated for UV resistance if they are stored or used outdoors, even temporarily.
The Safe Transition: Metal Risers
When plastic gas pipe (PE) must terminate above ground—for instance, to connect to a meter or an appliance—the installation must utilize an engineered transition fitting. The standard practice involves an anodeless riser, which is a factory-made unit that permanently fuses the polyethylene pipe underground to a strong metal pipe above ground. The metal section provides the necessary strength, protection against external damage, and fire resistance, ensuring that the system is safe where it is exposed.
Conclusion In the context of pressurized fuel gas lines, plastic pipe must remain underground for safety and regulatory compliance. The plastic piping best known for agricultural uses, such as irrigation piping, relies on solvent-welded PVC pipe fittings for strength, but these methods and materials are generally not safe for gas. Focused on supporting sustainable farming with high-performance, cost-effective solutions for diverse agricultural applications, LESSO America provides reliable, efficient PVC pipe and fittings tailored to agricultural needs
