EVOH composite pipes for Stage III vapor recovery stop fuel vapor permeation and corrosion under canopies and join by electrofusion.
Why Fuel Stations Need Barrier Composite Piping
Underground fuel lines must satisfy two conflicting requirements at the same time. They have to resist chemical attack from aggressive fuel blends, and they have to stop hydrocarbon vapor from leaking out through the pipe wall itself. Conventional smooth-wall HDPE pipe holds up well against corrosion, but thin-wall single-layer pipe still permits measurable permeation of gasoline-range hydrocarbons over the life of the installation.
An EVOH barrier layer directly addresses this. The ethylene vinyl alcohol film inside the Ai Yuan composite pipe acts as a gas barrier that sharply reduces permeation of gasoline and ethanol vapors, while the outer HDPE layer provides mechanical strength, UV resistance after backfill, and resistance to soil chemicals. Two otherwise identical-looking pipes can therefore behave very differently in service.
Material Structure of the Ai Yuan Composite Pipe
The Ai Yuan double-layer composite pipe is produced at Luoyang Wohong Petrochemical by co-extruding several materials through a single compounding line:
- Outer HDPE layer gives stiffness, handling toughness, and resistance to external loads.
- EVOH barrier layer sits inside and limits fuel vapor permeation.
- Conductive masterbatch is dispersed through the wall so the pipe can be electrically bonded and grounded, which is important in explosive-risk zones.
- Import-grade adhesive layers bond the EVOH film to the HDPE shells so the layers do not delaminate under bending or thermal cycling.
All Ai Yuan fittings are produced from imported PE raw material, and every electrical fusion fitting is a purpose-built electrofusion unit. This matters during installation because fitting compatibility is not optional with barrier pipe, it is the difference between a sealed joint and a slow leak.
Available Sizes and Their Typical Use
The range covers both straight lengths and coil forms so the correct pipe can be selected without unnecessary field joints:
- 125/110 and 110 sizes – double-layer and single-layer straight pipe, 6 m per length, used for main delivery headers and larger suction runs.
- 90 size – single-layer straight pipe, 6 m per length, used for branch runs.
- 75/63 double-layer – supplied as coil (100 m, 75 m, or 50 m per coil) and as 6 m straight lengths, giving flexibility for long trenchless or trenched runs.
- 63 single-layer – coil and straight options for smaller dispensing lines.
- 65/54 double-layer – coil (100 m or 50 m per coil), typically selected where tight routing under the dispenser island is needed.
When vapor-recovery return lines run parallel to the fuel supply line, using the same material grade for both avoids galvanic or chemical incompatibility and simplifies joint planning.
How Electrofusion Joining Works
Unlike solvent-welded or threaded steel systems, Ai Yuan composite pipes are joined with electrofusion fittings. A fitting containing an embedded heating coil is slipped over the prepared pipe ends, and a fusion machine drives a controlled current through the coil. The heat melts an interface zone, and as the material cools it forms an integral, pressure-rated joint.
The practical consequences for the installer are straightforward:
- Pipe ends must be cut square with a proper pipe cutter, not a hacksaw that leaves burrs.
- The fusion zone must be clean and dry. Water, dust, or grease in the joint area causes voids that may not show until pressure testing.
- The fusion machine must be matched to the fitting, and the recorded weld time and temperature data retained for traceability.
- Never fuse across a wet or cold pipe. In cold weather the fusion parameters need compensating, and the pipe should be warmed to the specified range before welding.
Because the fittings use imported PE material and are designed specifically for electrofusion, mixing them with generic couplings is strongly discouraged.
Integration with Stage III Vapor Recovery Piping
A Stage III system returns fuel vapors displaced at the dispenser nozzle back to the tank. The vapor line carries a saturated hydrocarbon-air mixture, so it benefits even more from a low-permeation pipe than the liquid line. Running both the liquid fill line and the vapor return line with EVOH barrier pipe keeps the two circuits consistent and minimizes the total vapor load reaching any monitoring or recovery equipment.
Key points for the contractor balancing these two circuits:
- Keep liquid and vapor line gradients positive so condensate drains toward the tank rather than pooling in low spots.
- Place joints where they remain accessible during the life of the station, even though electrofusion joints are permanent.
- Install the pipe in sand bedding with no sharp stones that could nick the outer layer.
- Ground the conductive masterbatch layer through the fitting system so static charge cannot build on exterior surfaces.
Pressure Testing and Leak Checks
Before backfilling, a composite fuel system must be verified under test pressure held for a defined period. The exact figure is set by project specification, but the discipline is the same everywhere:
- Pressure the entire liquid and vapor network to the test value.
- Hold the pressure and watch for decay beyond the allowable limit, not just for a wet joint.
- Isolate the tank side if it is not rated for the test pressure, and test the piping separately.
- Record the test result and the serial numbers of the electrofusion fittings used.
Because the system is designed as a sealed network, any joint that fails the test should be cut out cleanly and replaced with a fresh fitting, rather than patched or wrapped.
Handling, Storage, and Site Care
Barrier pipe is more than simple plastic because of its layered wall, and site handling reflects this:
- Store coils on a flat surface away from direct sunlight and sharp edges that can crease the wall.
- Never drag pipe over concrete or gravel during installation; use rollers or a pipe skid.
- Protect exposed ends with caps so dirt and moisture do not enter the bore before fusion.
- Mark the trench route and depth, and photograph joints before backfill for the as-built record.
Choosing Between Double-Layer and Single-Layer Pipe
The selection is a functional choice, not a cost-only one. Double-layer EVOH pipe is the rational choice for lines where vapor permeation and long service life matter most, namely the fuel supply and vapor return runs inside a dispenser canopy. Single-layer pipe remains a practical option for shorter, lower-risk branch connections where the added barrier is not required by the station design.
For a new retail fuel station, the cleaner engineering decision is usually to standardize on the barrier pipe across the whole network. It reduces the number of different materials on site, simplifies spares, and gives the station owner a single, consistent permeation specification from tank to dispenser.
Summary of Site Rules That Get Results
- Cut square, clean the fusion zone, and keep joint surfaces dry.
- Use the matching electrofusion fitting and the correct fusion machine settings.
- Bed the pipe in sand, expose no sharp stones against the wall.
- Ground the conductive layer and keep liquid and vapor gradients positive.
- Pressure-test the completed network, then record the results and fitting serials.
Follow these rules and an EVOH composite fuel system will deliver a tight, low-permeation, corrosion-resistant network that supports Stage III vapor recovery for the working life of the station. For site-specific sizes, coil lengths, and fitting selection, consult the Ai Yuan technical team at Luoyang Wohong Petrochemical before ordering so the pipe, fittings, and fusion equipment are matched to the project.