Underground pipelines are exposed to extremely high mechanical stresses, both during laying and in operation. This is particularly the case for trenchless laying by
- horizontal directional drilling (HDD),
- pile-driving, or
- steel pipe plowing.
Dynamic stresses from traffic loads or weather-related subsidence in the region of the trench also play a role here. Stresses of this type necessarily result in point loads, which are a local hazard for the corrosion-protection encasement of the pipes. Standard encasements based on polyethylene must therefore be embedded in rock-free material.
For non-conventional laying methods, such as trenchless laying, laying without a sand bed, or pipe insertion, which require additional mechanical protection for the polyethylene encasement, appropriate special solutions have been developed. These include
- a combination of polyethylene and fiber cement mortar, and
- additional FRP sheathing.
- VESTAMID® offers a solution for the most demanding requirements.
Multi-layer encasements have been successfully tested in which the outer layer of polyamide 12 serves for mechanical protection of the steel pipe.
Polyamide 12 from Evonik is already being used as a coating powder named VESTOSINT® for coating and lining of steel pipes and fittings for underground and underwater pipelines (in conformity with EN 10310). It is now also used as a granulate for the extruded outer protective layer for gas and water supply lines made of steel. VESTAMID® is processed on conventional extruders, as are commonly used for polyolefins in such applications, but the processing temperatures in the present case are somewhat higher.
Thanks to its superior mechanical properties, particularly at low temperatures, polyamide 12 is an excellent alternative to polypropylene:
- The Shore hardness D is higher.
- It is impact resistant at low temperatures.
- The tensile stress at yield is higher than for PE and PP.
- The elongation performance persists at lower temperatures.
Preliminary trials and pilot projects have successfully shown that VESTAMID® encasement provides a flexible and mechanically robust protective system for steel supply piping, which conceptually combines the advantages of a polyethylene encasement and a cement mortar sheathing.