Installing underground composite pipes at fuel stations is a precision job where small mistakes become buried, hard-to-reach failures. This guide covers the practical workflow for double-layer HDPE/EVOH composite pipes, the pipe and fitting range from Luoyang Wohong Petrochemical (Ai Yuan brand), and the field checks that separate a 30-year installation from a re-dig.
Why the Double-Layer Structure Matters Underground
The Ai Yuan double-layer composite pipe is produced by co-extruding HDPE with an EVOH barrier layer, conductive masterbatch, and imported adhesive through a single extruder. Each layer has a specific job:
- HDPE outer and inner layers provide mechanical strength, chemical resistance, and long-term structural integrity against soil loads and settling.
- EVOH barrier layer dramatically reduces hydrocarbon permeation, which is the leading cause of slow fuel migration through conventional single-layer PE pipe walls.
- Conductive masterbatch keeps the pipe wall static-dissipative, so fuel flowing through the line does not build a static charge that could arc to ground inside a tank pit.
- Imported adhesive bonds the layers so they act as one wall instead of delaminating under temperature cycling and flexural stress.
Every Ai Yuan fitting — elbow, tee, reducer, and transition fitting — is produced from imported PE feedstock and belongs to the electrofusion (EF) family. This matters because it lets you fuse pipe to fitting with the same electrofusion technique for every joint on the run.
Understanding the Product Range Before You Lay Out
Choose the pipe configuration from the actual line geometry, not just the nominal diameter:
- 125/110 double-layer composite pipe — rigid 6 m straight lengths for main distribution runs that need high flow and low pressure drop.
- 110 and 90 single-layer composite pipe — 6 m straight lengths for secondary lines where the EVOH barrier is built into the fitting or where permeation risk is lower.
- 75/63 double-layer composite pipe — supplied as coil (100 m, 75 m, or 50 m per coil) for long sweeping trench runs with few joints, and as straight 6 m lengths for short, rigid sections.
- 63 single-layer composite pipe — available as both coil and straight for service lines and vent lines.
- 65/54 double-layer composite pipe — coil form (100 m or 50 m per coil) for routing around tank pits and tight basement corners.
Coil product (75/63, 65/54) reduces joint count on long runs — fewer electrofusion welds means fewer places for leaks to start. Straight product (125/110, 110, 90) gives you rigid, predictable alignment for header and manifold sections where you want the line to hold a fixed gradient.
Pre-Installation Checks That Save the Job
Do these before a single trench is dug:
1. Verify Pipe and Fitting Compatibility
Confirm every fitting is an electrofusion type designed for the same PE material class as the pipe you are fusing. Mixing dissimilar PE grades on one EF joint is a common buried failure. All Ai Yuan fittings are EF and made from imported PE, so the whole run fuses consistently.
2. Inspect for Transport Damage
Check coil and straight pipe for ovality, deep scores, or creases at the bundle straps. An ovalized pipe will not seat evenly in the EF coupler, and that uneven gap is where weld quality fails.
3. Confirm the Trench Profile
The trench must be deep enough to place the pipe below frost line and above any utilities, with a graded sand bed to support the pipe along its full length. Never let the pipe bridge over rocks or hard spots — point loading causes stress cracking over years of soil movement.
4. Sweep the Pipe for Debris
Blow through each coil and length before installation and cap the ends. A single piece of gravel or a bird’s nest inside the line becomes a flow restriction and a maintenance call you cannot reach without excavation.
The Electrofusion Joint Procedure (Step by Step)
Electrofusion gives repeatable, verifiable joints if the procedure is followed exactly. The common field mistakes are haste and contamination, not the equipment.
- Clean and clamp — Remove any cutting burrs. Clean the fusion zone with the correct PE cleaner using lint-free wipes, and do not touch the cleaned surface with bare hands.
- Insert to the stop — Mark the insertion depth, push the pipe fully into the coupler until it seats, and clamp the fitting with the alignment clamps provided. The pipe ends must meet in the middle of the coil; a gap in the middle is a weld failure point.
- Connect and scan — Attach the EF machine leads to the terminal contacts and scan the barcode. The barcode carries the exact fusion time and energy for that fitting, so do not override it with a manual cycle unless you know why.
- Fuse without coolant — Once fusion starts, do not pour water or coolant on the joint. Cooling must be natural and undisturbed for the full cooling time printed on the fitting.
- Record the joint — Log every joint’s location, date, machine serial, and fusion data. This records becomes the inspection trail that commissioning engineers ask for.
For coiled runs, allow the coil to relax on the sand bed before fusing the final connections. A coil that is held under tension will try to straighten after the trench is backfilled, dragging the electrofusion joints and creating shear stress inside the coupler.
Gradient, Support, and Backfill
Underground pipe behaves like a beam. It needs continuous support, not point supports.
- Lay the pipe on a minimum of 100 mm of compacted, stone-free sand base.
- Maintain the design gradient toward the tank sump or collection point so condensed fuel and water drain by gravity; flat spots trap product and make leak detection slower.
- Backfill around the pipe with sand or fine aggregate in layers, compacting each layer evenly. Do not drop heavy stones or wheel a compactor directly over the pipe before at least 300 mm of compacted bedding protects it.
- At every change of direction, tuck the fitting into a slightly enlarged pocket in the trench floor so the fitting body is not the point of highest load.
Handling Thermal Movement
PE-based pipe expands and contracts more than steel. In a buried and backfilled line, the soil friction restrains most movement, but at expansion transitions and where the pipe leaves the trench to enter a tank pit, leave slack or an engineered expansion loop so seasonal temperature swings do not strain the joints.
Commissioning and Documentation
Before backfilling the last section, do a full air or hydrostatic pressure test on the assembled run in accordance with the project specification. Hold pressure for the required period, walk the whole run to check for audible leaks, and watch the pressure gauge for decay. After a successful test:
- Photograph every joint location and key the photos to the joint log.
- Apply the as-built drawing overlay showing pipe route, gradients, fitting locations, and depth.
- Hand over the electrofusion records to the station owner for the operating file.
A documented run is much easier to maintain, extend, or repair later — and it protects your company on warranty questions years down the line.
Maintenance and Inspection in Service
Once buried, the composite pipe needs little physical maintenance, but the system needs monitoring:
- Check the leak-detection and vapor-recovery system regularly; a properly installed double-layer EVOH line gives contaminant migration almost nothing to detect, so a sensor trip means a real event, not background permeation.
- Inspect sump and transition fittings on an annual basis for fuel odor, liquid, or condensate.
- Keep tank pit and sump sensors clean and calibrated so they maintain their sensitivity.
The double-layer EVOH design does not remove the need for leak detection — it removes the false positives and the slow background permeation that erode tank-warranty confidence. That is the practical difference a buyer notices over a five- to ten-year operating window.
Summary
Getting an Ai Yuan underground composite pipe run right is about preparation and discipline: matching EF fittings to the pipe, cleaning fusion zones, recording every joint, grading the trench, and supporting the pipe continuously. Do that, and the Luoyang Wohong Petrochemical double-layer HDPE/EVOH pipe delivers a long, low-maintenance service life buried under the forecourt.