14 Corrosion Under Insulation Defined simply, Corrosion Under Insulation (CUI) describes any type of corrosion that occurs due to moisture build up within the insulation system. CUI usually occurs between 0°C, and 120°C and is particularly critical above 60°C. CUI is hard to see without first removing the insulation, and facilities can have hundreds of kilometres of pipework that need to be manually inspected. It is also a serious problem that can shut plants down – often at a cost of millions per day. In extreme cases, corrosion has been known to trigger catastrophic safety incidents. The World Corrosion Organisation estimates that corrosion costs the global economy $2.2 trillion. Armacell offers insulation that satisfies the requirements of ASTM C692 – known as the ‘drip test procedure’ and offers low leachable chlorides when tested in accordance with ASTM C871 or EN 13468. Armacell’s insulation materials are also pH neutral. How does CUI occur? • Insulation covering is breached • Water ingress into the insulation • Water and oxygen reach the metal surface As well as CUI, water ingress can lead to system weight gain and a significant reduction in both thermal and acoustic performance. Insulation often requires replacement within a few years at high costs per linear metre. The highest incidence of leaks in the refining and chemical industries are due to CUI and between 40% and 60% of piping maintenance costs are CUI related. The problems caused by CUI have led to some industry sectors moving away from mineral wool insulation, since materials that are open cell have poor resistance to moisture. As a closed cell insulation, ArmaFlex drastically reduces the risk of CUI due to the insulation itself being a vapour barrier. The cost of replacing the pipework outweighs the cost of the insulation. So it is important to get the correct insulation specified to begin with. Stress Corrosion Cracking Austenitic Stainless Steel (types 304 & 316) can be sensitive to corrosive attack by soluble inorganic chlorides in the presence of oxygen and moisture, especially when, at the same time, the alloy is highly stressed. This is known as stress corrosion cracking (SCC). Chloride ions will always be present in the “normal building site environment” and may be deposited on the stainless steel surface during the handling and installation of all insulating materials. The presence of an insulation material, of any generic type, is more likely to concentrate chloride ions at the stainless steel surface. DIN 1988 limits the soluble chloride ion content of insulation products to 0.05% in order to protect against SCC. All ArmaFlex products meet the DIN 1988 requirements. The stress corrosion reaction is not usually significant at temperatures below about 50°C, but can be severe in the temperature range 50°C to 105°C. The most likely time that moisture may be present on the surface is when the plant is restarted after shut down. BS 5970 recommends that a barrier of aluminium foil, not less than 0.06mm thick, be applied to austentic stainless steel surfaces prior to the insulation. The standard also recommends, as an alternative to aluminium foil, that specially formulated anti-corrosive paints may be used for this type of application. However, the paint manufacturer’s instructions should be followed closely and the temperature limitations of the paint should not be exceeded. The Armacell recommendation is that where austenitic stainless steel is insulated then it is advisable to carry out the precautions outlined above irrespective of the operating temperature. The practical benefits of using Armaflex insulation: • Closed cell structure with a very high resistance to water vapour transmission • Ease of insullation so that all seems and joints may be sealed using ArmaFlex adhesive CORROSION