Key Installation Steps for Underground Composite Pipes at Fuel Stations
Proper installation is the single most important factor in the long-term performance of underground composite fuel pipes. At Luoyang Wohong Petrochemical, we produce the Ai Yuan brand HDPE/EVOH composite pipes, and our engineers see the same installation mistakes repeated on job sites year after year. This article covers the practical, field-tested procedures that protect your pipelay from day one.
Why Installation Quality Matters for Composite Pipes
An underground pipe system has to survive decades of soil pressure, traffic loads, temperature swings and fuel contact without leaking. The composite pipe itself — our 125/110 double-layer, 110 single-layer, 90 single-layer, and the 75/63 and 65/54 coiled variants — is designed for this duty. But even the best pipe fails if it is bedded, joined or backfilled incorrectly. Installation is where the real service life is decided.
Site Preparation Before Any Pipe Goes in the Trench
Check the Trench Profile
The trench must be straight, with consistent depth and a clean, continuous bed. Remove all sharp stones, construction debris and organic material from the invert. A poorly prepared bed causes point loading, which concentrates stress on a small area of the pipe wall. Over a full service life this is the fastest route to a fatigue failure.
Bedding Material
Use a fine, well-graded sand or pea gravel with a maximum particle size of about 10 mm. The bedding should be laid and lightly compacted to a uniform layer of roughly 100 mm under the pipe. Never place the pipe directly on hard subgrade or on large stones. The goal is a smooth, even support along the entire length of the run.
Handling the Pipe: Straight vs. Coiled
Ai Yuan supplies straight pipes in 6-meter lengths (125/110, 110, 90, and the 75/63 double-layer) as well as coiled pipe on drums (75/63 and 65/54, in 100-meter, 75-meter and 50-meter packs). Handling is different for each.
Straight Pipes
Unload straight pipes carefully to avoid impact damage. Keep them capped until the moment of installation to stop dirt and water from entering. During installation, support the pipe along its length — never let it bend sharply at the ends or rest on a single hard point.
Coiled Pipes
Coiled pipe must be unrolled, never dragged across the ground which can score the outer layer. Let the coil pay off naturally from the drum and straighten the pipe in the trench with gentle, even tension. Avoid kinking — a kink creates a permanent weak point that can crack under internal pressure later. The tighter the coil (75/63 and 65/54 are the tighter radii), the more care is needed during payoff.
Electrofusion Joining: The Core of the System
All Ai Yuan pipe fittings are electrofusion fittings made from imported PE raw material. Electrofusion joining is the method that holds the entire underground network together, so it deserves the most attention on site.
Prepare the Surfaces
Cleanliness is non-negotiable. Scrape the oxide layer from the pipe surface with a purpose-made scraper over the full length of the fusion zone, then wipe with a clean, lint-free cloth and an approved solvent to remove all grease, dust and moisture. Any contamination in the fusion zone is a potential leak path.
Alignment and Marking
Insert the pipe fully into the electrofusion fitting until it bottoms out against the internal stop. Mark the insertion depth on the pipe surface before pulling back, so you can always confirm the pipe did not shift during the fusion cycle. The joint must be straight and square — an angled joint produces uneven fusion around the circumference.
Run the Fusion Cycle
Follow the fusion parameters exactly as specified for the fitting and pipe size. Do not interrupt the cycle, and do not move or tension the joint while it is cooling. Fusion cooling is part of the joint integrity — pulling on the pipe too early strains the still-molten interface and creates a weak, partially fused joint.
Record Every Joint
Log each joint: date, operator, pipe size, fitting type, and the fusion machine settings used. This traceability is invaluable for future inspection, testing and maintenance of the underground network.
Backfilling Without Damaging the Pipe
Backfill is where most hand-over damage happens. The pipe can pass every fusion test and still be ruined by careless backfilling.
First Backfill Layer
Place the initial backfill over the pipe using the same fine, stone-free material as the bedding. Compact it evenly around and over the pipe in thin layers — typically not more than 150 to 200 mm per lift — until there is at least 300 mm of cover above the crown. Hand compact beside the pipe first, then use mechanical compaction only above this protective layer.
Never Drop Rocks on the Pipe
Do not tip coarse fill or rocks directly onto the pipe. The impact of a single large stone during dumping can dent or crack the pipe wall, and a hairline crack in an underground pressurised line may not show up until months later. Protect the pipe zone, then bring in general fill above it.
Detectable Warning Tape
Lay detectable warning tape in the trench above the pipe, at a distance specified by local practice, so future excavation crews know there is a fuel line beneath. This small step prevents accidental third-party strikes — one of the most common causes of underground pipe damage.
Pressure Testing Before Backfill Completion
Testing should be done in stages. Perform an initial pressure test on the completed pipe network before the trench is fully backfilled, so any leak can be located and repaired while access is still easy. Use the correct test medium and pressure for fuel pipe systems, and hold the test long enough to confirm stability. Confirm all fusion joints and fittings hold pressure before signing off the section.
Common Installation Mistakes to Avoid
- Skipping surface scraping — the oxide layer prevents a proper fusion bond.
- Moving the joint before cooling finishes — strains the molten interface.
- Poor bedding — point loading leads to fatigue cracks over time.
- Dropping coarse fill on the pipe — impact damage that is hard to detect later.
- Kinking coiled pipe during payoff — permanent weak points in the wall.
- No test before full backfill — leaks become expensive to find.
Final Hand-Over Checks
Before the trench is closed out, verify the full pipe run is bedded and covered correctly, every electrofusion joint is recorded, the network has passed its pressure test, and warning tape is in place. Keeping a photographic and written record of each stage gives the station owner a maintenance baseline for the life of the system.
Getting the installation right is not difficult — it is a matter of discipline. Correct bedding, careful handling of straight and coiled pipe, proper electrofusion procedure, controlled backfill and staged testing are the actions that turn a good composite pipe into a fuel station system that stays leak-free for decades.