Dear All:

Current pipe in pipe or multilayer pipe solutions for heat transport consist (from inside to outside) of metal inner pipe, Polyurethane isolation foam and a PE (Polyethylene) outer pipe.

My questions concern the following:

- Does diffusion of water and other molecules in ground water through Polyethylene influence the service life of these hot water pipelines, more specifically: does the metal inner pipe corrode by diffused water?

- What is the influence of joints and muffs on the water diffusion characteristics of these buried pipe in pipe solutions? How do welds influence the ageing and chemical degradation of these systems?

- What is the loss of thermal resistance if water diffuses into the PUR and CO2 is desorbed from the PUR foam as a function of time?

- If we would add an aluminium layer on the inside of the Polyethylene, would this give rise to blister growth in normal operating conditions (say temperature range -20 to 40 degr Celsius, atmospheric pressure and 100% water load on the PE)?

Thanks and looking forward to hearing from you,

Simon