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 town of Fortrose located on the Moray Firth, about 10 km north east of Inverness, was certainly no exception as the small coastal burgh is 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 challenging and 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.
Armaflex offered a number of benefits for this application over 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.
As a closed cell foam material, Armaflex 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 Armaflex 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 of Armaflex 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 Armaflex well exceeds these minimum requirements.
Due to its flexible foam structure Armaflex sheet can be easily cut and fabricated to cover fittings, pumps and valves. For outdoor use Armafinish 99 paint is required to provide protection against UV degradation. Alternatively HT/Armaflex 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) Armacell’s flexible Arma-Chek R covering or as was the case at Fortrose, metallic cladding can be used.
Owner of McDonald & Co thermal insulation contractors, Frank Cameron, has been an advocate of Armaflex insulation for many years and even during the exceptionally cold winters has never had any failures of equipment with the nitrile rubber material. Frank explained “on the large number of water facilities projects I have worked on over the years, Armaflex has offered the most reliable performance in cold weather. Add to this the ease of installation and affordability of the material, it is the best choice for providing frost protection in extreme weather conditions.”
For colder processes such as cryogenic applications, Armacell has recently developed Armaflex LTD utilising a diene terpolymer with a much lower glass transition point. This is the point (-50°C), where the mechanical behaviour of conventional nitrile rubber materials change, with the rubber increasingly losing flexibility through hardening. However, the Armaflex LTD products maintain full strength and flexibility over the temperature range of -200°C to +125°C. This ensures that vibration and impacts can be absorbed, with the risk of cracking from extreme temperature cycling or mechanical strain considerably reduced. The closed cell material has a very low thermal conductivity and also a high resistance to water vapour transmission providing a ‘built-in’ vapour barrier. These characteristics reduce the risk of CUI, providing significant savings on installation, while the cryogenic foams, unlike rigid foams, also eliminate the need for expansion joints or additional vapour barriers to achieve even further installation savings.
Further information is available on request:
Armacell UK Ltd, Mars Street, Oldham, Lancashire OL9 6LY
Telephone: 0161 287 7040 Fax: 0161 633 2685