Insulation protects WWT plant from weather extreme

Fortrose, UK – The Scottish Highlands are no stranger to cold weather but the winters of 2010 and 2011 were severe even for this part of the world, with temperatures regularly reaching -15 ºC. The costal town of Fortrose on the Moray Firth, about 10 km north east of Inverness, was no exception, being exposed to all the elements the cold North Sea has to throw at it.

So when Inverness based mechanical and electrical engineers Commissioning Solutions Scotland were appointed to replace failed process pumps for the local waste water treatment facility, careful consideration had to be given to the insulation material used to protect the equipment and process flows from freezing.

For this exposed environment David Hawthorn of Commissioning Solutions Scotland, working in conjunction with thermal insulation contractors McDonald & Co, specified Armacell’s Class O Armaflex nitrile rubber insulation material instead of the conventional glass fibre insulation material which had previously been used and failed on site.

Glass fibre or mineral wool insulation is reliant on an easily punctured external foil vapour barrier to prevent moisture ingress. If this barrier is compromised, the result is wet insulation that causes Corrosion Under Insulation (CUI) and loss of thermal performance, especially in tough conditions such as those encountered at the Fortrose waste water treatment works.

The closed cell foam material provides an integral vapour barrier against water ingress and condensation, with no additional water vapour barrier required. The material has a moisture resistance factor of >7,000 µ so even if the material becomes damaged in some places, it will still provide protection against condensation and water ingress as the closed cell structure is built-up throughout the material’s thickness.

The thermal conductivity of nitrile foam is 0.034 W/(m - K) at 0 ºC meaning, at outdoor temperatures of -15 ºC and initial line temperatures of 7 ºC, a 25mm layer will provide over 40 hours of frost protection on an 89 mm diameter steel pipe or 52 hours on a 114 mm diameter pipe when containing static fluids.

Local water supply regulations specify 12 hours protection at ambient temperatures of -6ºC, so the 25mm nitrile rubber product exceeds these minimum requirements.

Due to its flexible foam structure, the sheet can be cut and fabricated to cover fittings, pumps and valves. For outdoor use a UV protective paint is required, though a UV-resistant EPDM rubber material can be used without the need for additional painting.

For additional protection against mechanical impact (or even seagulls and rodents using the material for nesting) a special flexible covering or, as was the case at Fortrose, metallic cladding can be used.