Long underground runs are where composite fuel piping earns its keep — and where installation mistakes do the most damage. A gasoline station with wide tank-to-dispenser distances, several islands, and a long vapor return line will push pipe into the trench in coils rather than short pre-cut lengths. That saves joints and cost, but it also introduces a set of disciplines that a rigid-steel crew may not be used to: protecting the EVOH liner, pulling without kinking, laying out with the correct bend radius, and bedding the pipe so it is not crushed before it is even in service. This article walks through the practical rules for installing coiled double-layer and single-layer composite fuel pipe over long runs.
Why Coil Pipe Is the Right Choice for Long Runs
Composite fuel pipe is supplied in coils for several reasons. A continuous length of pipe removes most of the joints from a long run, which means fewer electrofusion welds to make, inspect, and document. Fewer joints also mean fewer potential leak points and a cleaner annular monitoring channel in double-wall systems. Coils deliver pipe that is easier to route around obstacles in the trench than rigid straight lengths, and the flexible material absorbs the small movements that soil settlement and temperature changes cause over time.
The trade-off is that the pipe arrives rolled up, and the rolled geometry has to be managed correctly during handling, payout, and installation. The EVOH inner liner and the antistatic layer that makes the pipe safe for fuel service are vulnerable to the kind of damage that careless uncoiling and dragging can cause. Protecting the pipe is the whole game in a long-run installation.
Handling and Storage: Protect the Pipe Before It Goes in the Ground
Coils should be stored flat, off the ground, and out of direct sun, protected from impacts and sharp objects. The pipe must never be dragged over curbs, gravel, or edges, because a cut or score on the outer surface can compromise the containment wall and a scratch through the liner can create a site for fuel permeation later. Use a payout stand or roll the coil off cleanly, keeping the pipe straight as it comes off the coil so it does not twist on itself.
Check every metre as the pipe is paid out. Look for flattened sections, cuts, gouges, or buckling. A pipe with visible damage should be cut out and jointed, never buried. In cold weather the pipe becomes stiffer and more prone to damage, so payout slowly and do not force tight bends while the material is cold.
Bend Radius: The Rule That Prevents Kinks
Every flexible composite pipe has a minimum bend radius that must not be exceeded. Forcing the pipe around a tighter curve than the material allows flattens the cross-section, pinches the liner, and can crimp the annular channel of a double-wall pipe. The practical habit is to sweep all changes of direction with long, gentle curves and to allow enough room at corners for the pipe to bend gradually.
Where a trench line must make a sharp turn, use a factory electrofusion elbow rather than trying to bend the pipe sharply on site. This is especially important in double-wall systems, where a kinked bend also breaks the continuity of the leak-detection annulus. If in doubt about a bend, make the radius larger — the only cost of a generous bend is a little more trench.
Laying Out the Run and Protecting the Liner
As the pipe is laid into the trench, keep a uniform slope along the run so liquid cannot pool in low spots. For a vapor recovery line, the slope should carry condensate back toward the tank rather than letting it sit in a sag. Support the pipe on a smooth, compacted bed so it is not resting on rocks or sharp material, and keep the pipe free of tension — a pipe that is pulled tight when it is trenched has no room to accommodate settling, and will be stressed the day it is buried.
The EVOH liner is what keeps fuel from permeating through the pipe wall, so protect it actively. Keep the open ends capped or covered while the pipe is in the trench so dirt, water, and debris cannot get inside. Do not step on the pipe and do not let heavy equipment cross it before it is bedded and covered.
Bedding and Backfill Around a Coiled Run
The bedding material around a composite pipe should be fine, free of sharp stones, and evenly placed. Place a smooth layer under the pipe, lay the pipe level on it, then add material around the sides and over the top in shallow lifts, compacting gently. Avoid dropping heavy or sharp backfill directly onto the pipe and avoid impact compaction directly above it. The goal is a pipe surrounded by uniform support, so it is not point-loaded by a single rock or a lump of clay.
For double-wall pipe, take care that bedding and compaction do not deform the pipe and pinch the annular channel. Compaction should firm the soil without crushing the pipe cross-section. Where the run approaches the tank or a dispenser, transition to the appropriate fittings, keeping the same care with alignment and support at every connection.
Verifying the Run Before It Disappears Underground
Before the trench is backfilled over the whole run, verify the work. Check that all bends are within radius, the slope is maintained, the pipe is not under tension, and the ends are clean and capped. For double-wall systems, confirm the annular channel is continuous with a blow-through or draw-wire test so you know the leak-detection probe can reach the far end. Photograph or record the exposed run so there is an as-built map of what is being buried. The more you verify while the pipe is still visible, the less you will excavate later to find a fault that could have been caught in minutes.
Coil pipe makes long underground fuel runs practical and economical, but the installation discipline has to match the material. Protect the EVOH liner from the moment the coil arrives, respect the bend radius, maintain the slope, and bed the pipe in clean, well-compacted material. Follow those rules and a long run will be as reliable as a short one — verified, documented, and ready to serve for decades.