PU Lining Systems
PU (Polyurethane) linings are designed to improve flow characteristics of the host pipe and protect against or prevent further corrosion.
When applied to a cleaned and prepared pipe, PU linings can eliminate or prevent further corrosion by forming an impermeable barrier between the flow within the pipe and the inner pipe surface. If thicker coatings are applied to a pipe they may offer a measure of leak protection and semi-structural integrity, similar to other coating applications. For small diameter pipes (non-man-entry), a thin layer of PU material is sprayed on using a high speed rotating nozzle. Usually, resin and hardener components are fed through separate hoses and mixed by a static mixer just before application to minimise potential for early hardening within the feed pipes. The speed of the head through the pipe and the liner material flow rate control the thickness of the coating. PU coatings normally cure after approximately 2 hours, but thicker coatings may take longer. PU coatings are also available for pipe rehabilitation and corrosion protection of large man-entry tunnels, water, and wastewater infrastructure. In these cases, coatings are applied manually using hand-held spray guns and, as with smaller diameters, a thicker application may offer a degree of leak protection and structural benefits. There is however a question over the status of this type of renovation as a structural option. In the USA in 2016 AWWA revised its M28 Water main rehabilitation manual and changed the landscape with a very clear statement much as follows: “To meet AWWA Class IV structural criteria, polymeric material must have the ability to essentially replace the host pipe in the event of a structural failure, and continue to perform on a long-term basis. Should the host pipe fracture, a Class IV spray-applied lining must separate from the host pipe much as Class III materials but have sufficient structural strength to function as an independent pipe under load and full working pressures. At the time of publication, there are no conclusive tests that demonstrate this ability for a commercially available spray applied lining.” This does not apply in Europe and the UK where there is no particular standard requiring this type of lining to perform in this way and to be considered structural.