The insulation structure of steel‑jacketed prefabricated direct‑buried steam insulation pipes is divided into inner‑sliding type and outer‑sliding type according to different sliding modes.
Inner‑sliding type (from inside to outside): The insulation structure consists of working steel pipe, drag‑reducing layer, aluminium silicate layer, microporous calcium silicate layer, stainless steel fastening band, aluminium foil reflective layer, polyurethane insulation layer, outer steel pipe and outer anti‑corrosion layer. (This type is basically obsolete at present.)
Outer‑sliding type (from inside to outside): The insulation structure is composed of working pipe, glass wool thermal‑insulation layer, aluminium foil reflective layer, stainless steel fastening band, sliding guide support, air insulation layer, outer‑jacket steel pipe and outer anti‑corrosion layer.
Super‑fine glass wool is generally adopted for the insulation layer. Aluminium silicate needle‑punched blanket can be used for higher‑temperature working conditions. The insulation layers are wrapped with staggered‑lap joints to achieve low heat dissipation and favourable air permeability. If the insulation layer gets water‑ingress during construction, moisture can be exhausted and the layer can be dried out gradually by raising steam temperature step‑by‑step. After drying, the shape and thermal‑insulation performance remain in good condition.
The guide support structure features low rolling friction, which facilitates the free expansion and contraction of the working steel pipe inside the outer‑jacket steel pipe. It reduces stress on fixed supports and greatly improves pipeline stability and safety. Thermal‑insulating material is applied between guide supports and the working steel pipe, which effectively solves the thermal‑bridge problem in the pipeline. Meanwhile, it prevents local corrosion damage to the anti‑corrosion coating of the outer‑jacket steel pipe.
Execution Standard: CJ/T 246‑2018, Prefabricated Direct‑buried Steam Insulation Pipes and Fittings for Urban Heating.
