Why Layered Pipe Construction Matters Underground
Underground fuel piping is the quiet workhorse of any service station. It never gets photographed, never makes the front page, yet it carries the lifeblood of the operation day after day, year after year. The material choice made at installation decides whether a station delivers fuel reliably for two decades or starts leaking in five. This article looks at the layered composite pipe systems used by customers of Luoyang Wohong Petrochemical — sold under the Ai Yuan brand — and how their construction translates into real-world behaviour in the ground.
A Pipe Is Not Just a Pipe
The pipes offered in this range are not simple single-wall products. They are co-extruded multilayer structures built from HDPE (high-density polyethylene), an EVOH barrier layer, a conductive masterbatch, and imported adhesive resin. The materials are fed into an extruder and fused into a single continuous composite wall. Each layer exists for a reason.
The HDPE forms the structural body — it gives the pipe its rigidity, its resistance to impact, and its ability to handle soil loads and thermal movement. The EVOH layer is the barrier: it is the part that dramatically slows the permeation of hydrocarbons and vapours through the wall, which matters in stations where groundwater protection is a design requirement. The conductive masterbatch ensures the pipe surface can be bonded to a grounding system, keeping static charge from building up as fuel flows through. The imported adhesive ties all these layers together into one seamless wall, so the pipe does not delaminate over time.
Reading the Model Numbers
The Ai Yuan range is laid out so the model number tells you what you are handling. A common format is two numbers separated by a slash, such as 125/110. This signifies a dual-layer composite pipe where the inner diameter relates to the first figure and the outer build to the second. A single number, such as 110 or 90, denotes the single-layer construction.
Straight Pipes, Six Metres Each
- 125/110 – double-layer composite, straight pipe, 6 m per stick
- 110 – single-layer composite, straight pipe, 6 m per stick
- 90 – single-layer composite, straight pipe, 6 m per stick
- 75/63 – double-layer composite, available as straight pipe at 6 m per stick
Coiled Pipes for Long Runs
- 75/63 – double-layer, coiled at 100 m, 75 m and 50 m per coil
- 65/54 – double-layer, coiled at 100 m and 50 m per coil
- 63 – single-layer, supplied in both coiled and straight form
Coiled product matters for a simple reason: fewer joints. Each joint in an underground fuel line is a potential weak point, no matter how well it is fused. A 100-metre coil lets a long fill line or vent run be pulled through a trench as one continuous piece, cutting the number of electrofusion joints to a minimum.
Electrofusion Fittings: One Family, One Method
All fittings in this range — every coupler, tee, elbow, and reducer — are electrofusion fittings, and they are manufactured from imported PE raw material. That single choice of material has a practical consequence for the installer: the fusion temperature profile and melt behaviour of the fittings are compatible with the pipe body.
Electrofusion works by heating a resistive wire coil embedded in the fitting. The fitting is slipped over the pipe ends, the coil is energised for a set time at a set voltage, and the heat melts both the inner surface of the fitting and the outer surface of the pipe. The two fuse into a homogenous joint. Because the wire trace can be read with a scanning device afterwards, electrofusion joints can be inspected and documented — a real advantage when a station needs records of its underground work.
Jointing Procedure, Step by Step
Getting a reliable electrofusion joint is not complicated, but it rewards discipline. The sequence below is the practice the authors recommend to installation crews working with single- and double-layer Ai Yuan pipe.
- Clean the surface. Wipe the pipe end with a clean, lint-free cloth to remove dirt, oil, and moisture. Contamination is the single most common cause of a failed fusion.
- Scrape the oxidation layer. Use the scraper supplied with the fitting to remove the outer skin of the pipe at the fusion zone. This exposes fresh PE for the melt. Skipping this step produces a joint that looks fine but may not be sealed.
- Mark and align. Mark the insertion depth on the pipe so the fitting seats fully and both pipe ends stay aligned. A misaligned joint stresses the fusion zone.
- Hold steady. The fitting must not move while it is heating. Use the alignment clamps to hold the joint rigid during and after the weld.
- Run the fusion cycle. Connect the fusion machine, set the parameters from the fitting’s data sheet or barcode, and start the cycle. Do not interrupt it.
- Cool, untouched. Leave the joint to cool for the time specified in the fitting instructions. Moving or loading a hot joint can pull it apart internally even when it looks fine from outside.
Working With Coiled Pipe
Coiled product needs a little more care during installation than straight sticks. The coil should be rolled out, not pulled roughly across the ground, to avoid kinking. As the pipe straightens, allow it to lie flat in the trench for a period before jointing so it relaxes into position. Trying to force a coiled section into a perfectly straight line while it is still springy will fight against you at every joint.
In a double-layer coiled pipe, be careful not to cut through both layers when trimming the end to length. A clean square cut is essential because a bevel or a ragged edge seats poorly inside an electrofusion fitting and can compromise the seal.
Backfill and Bedding
Even the best pipe fails if the trench is handled badly. The pipe should sit on a bed of clean, compacted sand or fine granular material free of sharp stones. Backfill around the pipe should be placed in thin layers and compacted evenly, never dumped in a single heavy lift that can crush or shift the pipe. Sharp rocks and debris in the backfill are a common cause of external damage that is only discovered years later.
For double-layer pipe, the conductive masterbatch in the wall means the outer surface can be earthed to the station grounding network. Confirm the grounding connection is made before backfilling, because it is far easier to attach a clamp to an exposed pipe than to one buried under a metre of soil.
Pressure Testing Before Burial
No matter how carefully the joints are fused, the entire run should be pressure-tested before the trench is backfilled. An air or hydrostatic test at the pressures recommended for the pipe size will reveal a bad joint while it is still cheap to fix. Mark the test results and keep them on file. The records become part of the station’s maintenance history and make future inspections easier.
Choosing Between Single and Double Layer
The practical question most buyers ask is when single-layer is enough and when they should specify the double-layer build. The answer is driven by the duty and the environment.
Single-layer 110, 90, and 63 pipe is well suited to applications where vapour permeation is less critical and cost per metre is the deciding factor. Double-layer 125/110, 75/63, and 65/54 adds the EVOH barrier, which is specified when the station sits above sensitive groundwater or when local practice requires a low-permeation system for liquid and vapour lines.
The double-layer product also tends to be chosen for the main product lines where vapour recovery is a design goal, because the barrier layer limits fugitive emissions over the life of the pipe. When in doubt about a specific project, the engineering team should review the local requirements and choose the layer construction that matches the risk profile of the site rather than defaulting to the cheapest option.
Conductivity and Grounding
Fuel flowing through a plastic pipe generates static charge on the interior wall. In an all-metal system that charge dissipates to earth through the metal. In a plastic system it has nowhere to go unless the pipe is designed to be conductive. The conductive masterbatch in the outer layer gives the Ai Yuan range that path, but only if it is connected. Every station should verify that the conductive layer is bonded to the grounding electrode system and tested at regular intervals.
Planning for the Long Service Life
An underground fuel system is installed once and expected to outlast several refits of the pumps and tanks above it. The practical decisions — which layer construction, straight or coiled, how the joints are fused, how the trench is bedded, whether grounding is attached before burial — are what determine whether that expectation is met.
Luoyang Wohong Petrochemical supplies the Ai Yuan range of HDPE/EVOH composite pipes, electrofusion fittings, and coiled product for stations that want the details handled properly. The product information in this article is offered for the guidance of engineers, purchasers, and installation contractors planning their next underground piping project.
For specific sizing, jointing parameters, or project guidance, contact WoHong Petrochemical International Department.