Key Considerations for Underground Composite Pipe Installation at Fuel Dispensing Stations

Key Considerations for Underground Composite Pipe Installation at Fuel Dispensing Stations

Proper installation of underground piping systems is critical to the long-term safety and reliability of any fuel dispensing station. Unlike above-ground plumbing, buried fuel lines face continuous soil pressure, groundwater exposure, temperature fluctuation, and potential traffic loads. This article covers the practical technical aspects of installing HDPE-based composite pipes for underground fuel transport, drawing from field experience with the Ai Yuan brand composite piping systems manufactured by Luoyang Wohong Petrochemical.

Site Preparation and Trench Specifications

Before any pipe is laid, the trench must be prepared to specification. The trench width should be at least 40 cm wider than the pipe diameter on each side to allow proper bedding and backfill compaction. For Ai Yuan 110 mm and 125 mm straight pipes, this means a minimum trench width of approximately 50–55 cm. The trench depth must account for frost line depth in colder regions, typically 60–90 cm minimum cover over the pipe crown.

The trench bottom must be leveled and free of sharp rocks, debris, or uneven surfaces. A 10 cm layer of fine sand or pea gravel bedding material should be spread and compacted before pipe laying. This bedding layer provides uniform support and prevents point loading that could damage the pipe over time.

Handling and Storage of Composite Pipes Before Installation

Ai Yuan composite pipes come in both straight 6-meter sections and coiled forms depending on the diameter. The 75/63 and 65/54 mm flexible double-layer composite pipes are supplied in coils of 100 m, 75 m, or 50 m, while 125/110, 110, and 90 mm pipes are straight sections.

Coiled pipes should be stored on a flat surface and unrolled carefully without kinking. For straight pipes, support them along their full length to prevent sagging and deformation. All pipe ends should remain capped during storage to keep out dirt and moisture. Direct sunlight exposure should be minimized — while HDPE has UV resistance, prolonged storage under direct sun is not recommended.

Pipe Jointing Procedures for Ai Yuan Electrofusion Fittings

All Ai Yuan pipe fittings are electrofusion fittings made from imported PE raw material. The electrofusion process creates a homogeneous, leak-proof joint that is as strong as the pipe itself. Follow these steps carefully:

Step 1: Surface Preparation

Clean the pipe end thoroughly using a clean, lint-free cloth. Remove all dirt, grease, moisture, and oxidation. Use a pipe scraper or peeling tool to remove the outer oxide layer from the pipe surface where the fitting will sit. This scraping depth is typically 0.2–0.3 mm and should extend 5–10 mm beyond the fitting length. For Ai Yuan double-layer pipes (125/110, 75/63, 65/54), the outer layer is HDPE but the preparation method is the same — the fusion joint is made on the outer HDPE surface.

Step 2: Alignment and Clamping

Insert the prepared pipe end into the electrofusion fitting until it reaches the internal stop. Ensure the pipe is straight and the fitting is square. Use the appropriate clamping tool to hold the pipe and fitting in position during fusion. Ovality correction may be needed if the pipe has been stored in a coil — use an ovality correction tool or rounder to bring the pipe end back to round before insertion.

Step 3: Fusion Welding

Connect the electrofusion welder leads to the fitting terminals. Scan the barcode on the fitting or enter the fusion parameters manually — all Ai Yuan electrofusion fittings have embedded resistance wire patterns with specific voltage and time requirements. The welder will automatically control the fusion cycle. Typical fusion time ranges from 80 to 200 seconds depending on the fitting size.

During fusion, a small bead of molten material should appear at the indicator holes on the fitting — this is the visual confirmation that proper fusion has occurred. Do not disturb the joint during the cooling period, which is usually 10–20 minutes depending on ambient temperature.

Step 4: Cooling and Inspection

Allow the joint to cool naturally without forced cooling (no water, no compressed air). Forced cooling can create internal stresses and weak joints. After cooling, visually inspect the bead at the indicator holes and check for any visible gaps or misalignment. A properly made Ai Yuan electrofusion joint will have a uniform melt bead and no leakage path.

Trench Backfill and Compaction

After all joints are completed and inspected, the pipe is ready for backfill. The first layer should be 15–20 cm of fine granular material (sand or 5 mm minus gravel) placed and hand-compacted under and around the pipe. This initial cover protects the pipe from damage during the main backfill operation.

Continue backfill in 20–30 cm lifts, compacting each layer to at least 90% of standard Proctor density. Heavy compaction equipment should not come within 30 cm of the pipe until there is at least 30 cm of cover. For Ai Yuan 125/110 mm pipes under roadways or parking lots, consider concrete encasement or a reinforced concrete slab above the pipe zone for additional protection.

Leak Testing After Installation

Once the piping system is fully installed and backfilled, conduct a pressure test before putting it into service. Test the system at 150% of the maximum operating pressure (typically 50–60 psi for vapor recovery applications). Hold the test pressure for at least 30 minutes with no measurable drop. For Ai Yuan’s double-layer pipe systems (125/110, 75/63, 65/54), the interstitial space between the inner and outer layers provides an additional leak detection channel that can be monitored continuously in service.

Common Installation Mistakes to Avoid

Based on field experience with Ai Yuan composite pipe installations across multiple fuel stations, here are the most frequent problems encountered:

• Insufficient scraping — Not removing enough of the oxide layer leads to weak fusion joints. Always measure and verify the scraped length.
• Moisture contamination — Water on the pipe surface during electrofusion creates steam pockets that weaken the weld. Keep all components dry.
• Improper clamping — Loose clamping allows the pipe to push out during fusion, resulting in incomplete joint penetration.
• Skipping cooling time — Loading the joint before it has fully cooled causes residual stress and potential failure.
• Sharp bends on coiled pipes — The minimum bend radius for Ai Yuan 75/63 coil pipes is 20 times the pipe diameter. Tighter bends create stress points.

Long-Term Performance and Maintenance Considerations

Ai Yuan composite pipes use a multilayer structure: HDPE outer layer for mechanical strength and corrosion resistance, EVOH barrier layer for hydrocarbon permeation resistance, conductive inner layer for static dissipation, and imported adhesive bonding the layers together. This construction gives the pipe a design life well beyond 30 years when installed correctly.

Regular monitoring of the interstitial space vacuum or pressure in double-wall systems provides ongoing leak detection without excavation. For single-wall systems (110 and 63 mm), periodic line tightness testing every 3–5 years is recommended. Cathodic protection is not required for HDPE-based composite pipes since they do not corrode, which is a significant advantage over steel piping in underground fuel service.

Proper installation is the foundation of a long-lasting underground fuel piping system. Attention to joint quality, backfill procedures, and testing protocols will ensure that the Ai Yuan composite piping system delivers reliable service for decades.