Working pipe + rigid polyurethane foam + HDPE casing, plus steel-jacket steam pipe and overhead mineral-wool composite for higher temperatures. Structures selected by medium temperature, not by habit.
Spiral, ERW or seamless, hydro-tested before foaming. Wall thickness set by design pressure, not by the foam.
Density ≥ 60 kg/m³, closed-cell ≥ 88%, poured in the cavity and bonded to both walls so the three layers act as one.
Waterproof and abrasion-resistant; the only barrier between the foam and groundwater. Damaged casing equals wet foam equals no insulation.
Optional but strongly advised: a wire run inside the foam turns an invisible leak into a located point on a monitor.
Cut a sample and look at three things: foam cells — fine and uniform means the pour was right; foam-to-steel bond — it should tear, not peel off clean; casing wall — even thickness all round, no ovality from storage.
We pour on a tilting platform so the foam fills the annulus evenly along the whole length — the end where the pipe was standing still is where bad insulation shows up first.
Indicative figures for a buried hot-water line (soil 5 °C, 90 °C medium). Actual results depend on burial depth, soil moisture and joint quality — we calculate per project on request.
| Nominal dia. | Bare pipe loss (W/m) | With 50 mm PU (W/m) | Reduction | Temperature drop per km |
|---|---|---|---|---|
| DN200 | ≈ 210 | ≈ 19 | ≈ 91% | 0.6 – 0.9 °C |
| DN500 | ≈ 290 | ≈ 24 | ≈ 92% | 0.3 – 0.5 °C |
| DN800 | ≈ 360 | ≈ 29 | ≈ 92% | 0.15 – 0.25 °C |
| DN1200 | ≈ 430 | ≈ 34 | ≈ 92% | 0.08 – 0.15 °C |
Rule of thumb: the larger the diameter, the less each kilometre costs you in temperature — and the more the joints matter.
HDPE casing + rigid foam + carrier. Stored outdoors, laid straight into the trench.
Outer steel jacket carries the load and the expansion; inner supports keep the carrier centred.
Layered wool or aluminium silicate with cladding — repairable, for steam mains and plant racks.
Large-diameter insulated pipe uses the spray-and-wrap process: the steel pipe rotates while polyurethane is sprayed on layer by layer, then the jacket is wound on continuously — no pre-made casing, insulation and jacket formed as one piece. Skip a step here and it shows up years later as a cracked jacket, water ingress and rising heat loss.
Heat number and mill certificate checked first, NDT re-verified, then full shot blasting. A poor surface means the foam will not bond — and you get voids later.
The pipe rotates at constant speed while mixed polyurethane is sprayed on pass after pass. Layer thickness and density are controlled online with no delamination; insulation thickness is freely adjustable, not limited by any casing size.
While the foam is still fresh, PE (or FRP) tape is heated and spiral-wound over the insulation, laps fusion-bonded into a continuous seamless jacket locked to the insulation layer.
Waterproof caps or heat-shrink sleeves on both ends, sealant on the end face. Open ends are what kills pipes in storage and sea freight.
Holiday test on the casing, dimensional re-check, continuity test on the detection wire; specification and heat number marked on the pipe.
Casing cut square, foam removed to the exact welding length, end faces dry and dust-free.
Carrier welded to the qualified WPS, NDT on the joint, pressure test before anything is closed up.
Same chemical system as the plant, injected in one shot, density and fill checked at the joint.
Heat-shrink sleeve or electrofusion band, overlap to spec, then a holiday test on the finished joint.
We would rather tell you this plainly: a 10 km line has 800–900 joints, and every one of them is a hole waiting to happen if the procedure is skipped. That is why we supply the joint kit, the procedure card and — if you want — the crew.
Two tinned copper wires run the whole length inside the foam. Water reaching them changes the loop resistance; the monitor converts that into a distance reading, so the repair crew opens one pit instead of ten.
Recommended for trunk mains, river and road crossings, and any section where excavation is expensive. Wire type, loop layout and monitor brand are agreed at design stage.
| Standards | GB/T 29047 · CJJ/T 81 · GB/T 28638 · SY/T 0415 · GB 50264 |
| Structures | Direct-buried PU · steel-jacket steam · overhead mineral wool / aluminium silicate |
| Diameter | Carrier DN15 – DN1400 · casing up to Φ1500 |
| Foam | Rigid PU, density ≥ 60 kg/m³, closed cell ≥ 88%, compressive strength ≥ 0.3 MPa |
| Casing | HDPE PE80 / PE100, wall thickness to GB/T 29047 |
| Service temperature | PU ≤ 120 °C · steel jacket 120–350 °C · mineral wool ≥ 350 °C (overhead) |
| Joints | Field pour + heat-shrink sleeve / electrofusion band / welded steel jacket |
| Options | Leak-detection wire · warning tape · end seals · prefabricated bends and tees |
| Inspection | Foam density and closed cell · bond strength · casing thickness · hydrostatic test on carrier |
Direct burial saves the trench civil works, is faster and takes less land — the mainstream for district heating. A trench is easier to inspect but costs more and needs drainage. Use a trench where the water table is high, the soil is soft, or frequent access is required; direct-bury the rest.
For trunk mains, crossings and access-restricted sections, yes — it turns an invisible leak into a located point. For short internal runs where excavation is cheap, it can be skipped.
Best: our crew, or yours following our procedure card with our kit. The joint is the weakest link — wrong foam ratio or a sleeve overlap 20 mm short is enough to flood a whole section.
Technical proposal and quotation within one working day.
