1. Introduction
Installing underground composite piping systems at retail fuel stations is a precision job that directly affects long-term operational safety and maintenance costs. Unlike steel or fiberglass piping, HDPE+EVOH composite pipes have different handling, jointing, and backfill requirements. This article walks through the practical installation workflow for Luoyang Wohong Petrochemical’s Ai Yuan composite pipes, covering trench preparation, pipe laying, electrofusion jointing, pressure testing, and backfill procedures.
2. Pre-Installation Site Preparation
2.1 Trench Design and Dimensions
Before any pipe leaves the crate, the trench layout must be verified against the station’s piping and instrumentation diagram. For Ai Yuan composite pipes, minimum trench width should be pipe outer diameter plus 400 mm on each side to allow room for jointing work. Trench depth depends on frost line and vehicular load — typically 750–900 mm from finished grade to pipe crown for service station driveways.
2.2 Bedding Material
The pipe must rest on a 100–150 mm compacted sand or fine gravel bed with a maximum particle size of 10 mm. Sharp rocks or construction debris in the bedding layer cause localized stress points that can, over years of thermal cycling and ground movement, compromise the pipe wall. The bedding material should be compacted to at least 90% Standard Proctor density before pipe laying begins.
3. Handling and Storing Ai Yuan Composite Pipes
3.1 Straight Pipe (6 m Lengths)
Model 125/110, 110, 90, and 75/63 straight pipes come in 6-meter sections. They should be stored on flat ground with wooden blocks spaced at 1.5-meter intervals to prevent sagging. When lifting, use fabric slings — chains or wire ropes will gouge the HDPE outer layer. For the 125/110 double-layer composite pipe, extra care is needed at the ends where the EVOH barrier layer is exposed.
3.2 Coiled Pipe (50–100 m Coils)
Models 75/63 and 65/54 come as coiled pipe for flexible routing. Coils should be stored upright and unrolled using a coil trailer or turntable. Never drag a coil across asphalt or concrete — the abrasive surface will score the pipe wall. The minimum bend radius for Ai Yuan coiled pipes during installation is 20 times the outer diameter, so for 75/63 pipe this works out to about 1.5 meters. Sharper bends risk kinking the EVOH barrier layer.
4. Electrofusion Jointing Procedure
4.1 Preparation of Joint Area
All Ai Yuan pipe fittings are electrofusion fittings made from imported PE raw material. The jointing process starts with pipe end preparation:
- Cut the pipe end square using a wheel-type pipe cutter — never use a saw, which leaves burrs that interfere with fusion
- Scrape off the oxidized surface layer from the pipe using a manual scraping tool, removing 0.2–0.3 mm of material over the full fusion zone length
- Clean the scraped area and the inside of the electrofusion fitting with isopropyl alcohol and a lint-free cloth
- Mark the insertion depth on the pipe with a permanent marker
4.2 Clamping and Alignment
Insert the pipe into the electrofusion fitting up to the depth mark, ensuring the pipe bottoms fully against the internal stop in the fitting. Use the alignment clamp (centralizer) to hold both pipe and fitting concentric. Misalignment is the single most common cause of fusion failure — the gap between pipe and fitting should be uniform all around. Check ovality: if the pipe is out of round by more than 1.5%, use a rounding clamp before inserting.
4.3 Fusion Cycle Parameters
Connect the electrofusion welding machine leads to the fitting terminals. For Ai Yuan fittings, the standard parameters are:
- Input voltage: 39.5 V ± 0.5 V
- Fusion time: varies by fitting size (typically 90–180 seconds as marked on the fitting barcode)
- Cooling time: do not move or pressure-test the joint during the cooling period (typically 10–20 minutes depending on ambient temperature)
The welding machine reads the barcode on each fitting and automatically sets the correct time and voltage. Do not override these parameters unless the manufacturer explicitly directs otherwise. During fusion, a small bead of molten PE should appear at the indicator ports — this confirms proper melt flow.
4.4 Cooling and Visual Inspection
After the fusion cycle completes, allow the joint to cool without any external force or movement. The cooling time printed on the fitting label is the minimum. In cold weather (below 5 °C), double the cooling time. After cooling, inspect:
- Indicator pins at the fitting ports should be flush or slightly protruding
- No visible gaps between pipe and fitting
- No leakage, discoloration, or burn marks on the fusion zone
5. Backfill and Compaction
5.1 Initial Backfill (Pipe Zone)
The backfill material in the pipe zone — from trench bottom to 300 mm above the pipe crown — must be the same quality as the bedding material: sand or fine gravel, maximum particle size 10 mm, no sharp edges. Place backfill in 150 mm lifts and compact each lift with a hand tamper or plate compactor. Never operate heavy compaction equipment directly over the pipe until at least 600 mm of cover is in place.
5.2 Warning Tape and Final Backfill
Lay detectable warning tape 300 mm above the pipe crown. For Ai Yuan composite pipes, which are non-metallic, detectable tape with an embedded aluminum foil layer is essential for future locateability. The final backfill (above the pipe zone) can use native excavated soil provided it is free of rocks larger than 50 mm and organic material. Compact to 95% Standard Proctor density for paved areas.
6. Pressure Testing the Completed System
6.1 Test Procedure
After all joints are cooled and at least 24 hours post-installation, conduct a hydrostatic pressure test:
- Fill the system with water and vent all air at high points
- Pressurize to 1.5 times the maximum working pressure (typically 4.5 bar for station piping)
- Hold the test pressure for 2 hours, monitoring with a calibrated pressure gauge
- Pressure drop should not exceed 0.2 bar during the test period
6.2 What to Check After Testing
After pressure testing, walk the entire trench and inspect all exposed joints. Any sign of moisture or seepage means a joint needs to be cut out and re-fused with a new fitting — never attempt to patch a failed electrofusion joint. Label each successfully tested section with the date and test pressure for the installation record.
7. Common Installation Mistakes to Avoid
Based on field experience with Ai Yuan composite pipe installations across service station projects, these are the most frequent errors:
- Skipping surface scraping — the oxide layer on HDPE prevents fusion bonding. Even on a new pipe, scraping is mandatory.
- Insufficient cooling time — some crews rush the cooling process and move the pipe or pressurize the system. This creates a cold joint that looks fused but will separate under pressure.
- Poor trench drainage — if groundwater collects in the trench during installation, it can float the pipe or wash away bedding material. Keep sump pumps ready.
- Over-compaction directly on pipe — a vibrating plate compactor run directly on the pipe wall can cause denting and ovality that leads to joint misalignment.
- Mixing pipe brands in one run — different manufacturers have different fusion parameters even when the material says HDPE. Stick with one brand (Ai Yuan) throughout the project.
8. Conclusion
Proper installation of underground composite pipe systems is the difference between a maintenance-free fuel station piping network and one that develops leaks within the first few years. For Luoyang Wohong Petrochemical’s Ai Yuan HDPE+EVOH composite pipes, the critical steps are correct bedding material, thorough electrofusion jointing procedure, adequate cooling, and careful backfill. Following these practical guidelines ensures the piping system delivers its intended service life of 30+ years under fuel station operating conditions.