Most of the joints on a composite fuel pipe project are electrofusion, and most of the leaks that appear later trace back to one of three things done carelessly: surface preparation, insertion depth or cooling. The machines are simple; the discipline is what varies from crew to crew.
Surface Preparation Before Welding
The pipe outer wall oxidizes while in storage, and that oxide layer sits between the heating coil and the pipe during fusion. Scrape the full insertion length with a purpose-made scraper until clean material shows, then keep hands and dirt off the fresh surface. Scrape and weld the same day; a prepared end left overnight has started oxidizing again.
Insertion Depth and Marking
Measure the insertion depth for the fitting in use and mark it on the pipe end with a full-circle line. When the pipe is inserted, the line should sit just at the coupler mouth. Push in square to the axis, slowly; a skewed insertion drags debris in and can score the coil. Depth matters in both directions: short insertion leaves fusion zones partly unfused, while bottoming out leaves melted material nowhere to flow.
Cooling Without Disturbance
Strength in an electrofusion joint forms during cooling, not during welding. The interval while the joint is still soft is exactly when a hurried crew moves pipe, backfills or steps on it. Hold the joint still for the cooling time stated for the fitting, and let the ambient temperature version of that time apply, which in cold weather is longer than the number crews remember from summer.
Inspecting the Finished Joint
A sound joint shows uniform witness indicators raised and a small, even melt bead at both coupler ends. No witness movement, a one-sided bead or a visibly distorted coupler gets recorded for review, not buried and forgotten. Number every joint on the drawing; when a pressure test flags a drop, an as-built joint log turns a day of digging into an hour.
| Stage | Practice | Common error |
|---|---|---|
| Surface prep | Scrape to clean material | Recontamination before insertion |
| Insertion | Mark depth, square push-in | Short insert or bottoming out |
| Cooling | Full time, no movement | Early backfill or handling |
| Inspection | Witness and bead check, joint log | Anomalies left unrecorded |
Frequently Asked Questions
Where do fusion parameters come from?
Follow the pipe manufacturer’s stated voltage and time for the size and ambient conditions, and do not mix parameters between brands of pipe and fittings.
Can a scraped end sit overnight?
No. Re-scrape before welding; oxide regrows on exposed surfaces and blocks fusion.
What changes in cold weather?
Cooling times extend and cold fittings store better in a warm space before use. Slower work in winter prevents most cold-season joint problems.
Does VOHON support electrofusion practice on its composite pipe?
Yes. VOHON supplies composite fuel pipe with jointing and installation guidance, and answers field questions by email at lixiang@vohon.cn.