Underground fuel lines carry a serious responsibility. Buried beneath service station forecourts, they must keep gasoline and diesel contained for decades without leaking into soil or groundwater. The material choice for these lines is therefore one of the most important engineering decisions a station owner or contractor makes. Double-wall composite pipe with an EVOH inner lining has emerged as a practical, field-proven answer to this challenge.
What Makes Double-Wall Composite Pipe Different
A double-wall composite pipe is not a single plastic tube. It is a layered system. The inner pipe, which carries the fuel, is lined with EVOH resin. This lining gives the pipe its strong permeation resistance, which is the property that matters most when gasoline sits in contact with the pipe wall for years. The outer wall is built from imported HDPE, which provides mechanical strength, impact resistance, and protection against the surrounding soil and traffic loads above.
Between the two walls there is a detectable interstitial space. In a properly installed system, this annular space is connected to monitoring points, so a leak in either wall can be detected and located before fuel reaches the environment. This monitoring capability is a core reason why regulators and engineers favor double-wall designs for high-risk fuel applications.
The EVOH Lining and Why It Matters
Hydrocarbon liquids, especially oxygenated fuels, can slowly permeate through ordinary polyethylene. Over decades, even small permeation losses add up. EVOH (ethylene vinyl alcohol) has one of the lowest permeation rates among common thermoplastics, which is why it is used as the inner barrier layer in composite fuel piping. The EVOH lining in Vohon Aiyuan double-wall pipes is applied as a continuous layer inside the inner tube, giving the fuel a stable, low-permeation surface for the full length of the run.
The same inner pipe also carries an antistatic layer with a surface resistance below 10 to the power of 6 ohms. Static electricity is a real hazard around flammable liquids. The antistatic layer helps dissipate charge safely, reducing the risk of static ignition during fuel flow and transfer operations.
Working Pressure and Temperature Range
Vohon Aiyuan double-wall composite pipes are rated for a working pressure of 1 MPa, which comfortably covers the operating conditions of gravity-fed and pressure-fed fuel delivery systems at service stations. The nominal operating temperature range is minus 40 to plus 50 degrees Celsius, so the pipe performs reliably across hot desert climates and cold northern winters. Both self-priming and pressure-type systems can be used with this pipe, which gives designers flexibility when laying out the station.
Electrofusion Jointing: Fast and Flame-Free
Jointing is where many underground piping projects go wrong. Poor joints are the most common source of leaks. The Aiyuan system uses electrofusion welding, a method in which an electric current heats a built-in heating coil inside the fitting, melting the pipe surface and the fitting together into a single homogeneous joint.
Electrofusion has two practical advantages on site. First, there is no open flame, which is a significant safety benefit in a fuel handling environment. Second, the welding process is controlled by the fusion unit rather than by operator skill, so joint quality is consistent and repeatable. Installation is fast: joints cool in minutes, and the trench can be backfilled without long waiting periods.
A Complete Fittings Range for Real Projects
A piping system is only as good as its fittings. Vohon Aiyuan supplies a full range of electrofusion fittings for double-wall pipe, including 90-degree elbows, tees, couplings, reducers with and without test terminals, copper threaded terminals, and steel flange terminals. For single-layer lines, the range covers 90-degree and 45-degree elbows, tees, couplings, flange terminals, non-welded reducer joints, and antistatic plug-in connectors.
Pipe is available in standard sizes to match the fitting range. Double-wall models include AY-01-65/54 (54 mm), AY-01-75/63 (63 mm), and AY-01-125/110 (110 mm), with lengths from 1 m up to 100 m depending on model. Single-layer models cover 63 mm, 90 mm, and 110 mm diameters. Because the fittings and pipe come from the same manufacturer, dimensional matching is guaranteed, and fewer adapters are needed on site.
Installation Considerations for Contractors
Correct installation starts before the pipe enters the trench. Bedding should be clean sand or fine gravel, free of sharp stones that could damage the outer wall. Pipe should be laid with gentle bends rather than forced curves, and the annular monitoring space should be connected according to the system layout drawing. After jointing, a pressure test should be carried out before backfilling, and the test record kept with the station documentation.
For stations being upgraded from single-wall to double-wall systems, the change is straightforward because the same electrofusion jointing method is used. Site crews familiar with HDPE fusion work can be trained on the double-wall procedure in a short time.
Long-Term Cost Picture
Double-wall composite pipe costs more per meter than ordinary single-wall pipe, but the total cost of ownership tells a different story. The monitoring capability reduces the risk of undetected leaks, which protects against remediation costs, regulatory penalties, and reputational damage. The EVOH lining preserves product quality by preventing permeation losses. And because the pipe is supplied with matching fittings from a single source, procurement is simpler and installation is faster, which lowers labor cost on site.
For underground fuel piping projects where environmental protection, operational safety, and long service life are priorities, double-wall composite pipe with EVOH lining is a well-proven choice. It combines the strength of HDPE with the barrier performance of EVOH, and it brings detection capability that single-wall systems simply cannot offer.