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44 Spring 2019 outer cladding, or condensation formed during the refining or purifying process. As this moisture accumulates beneath the insulation, the water does not have the opportunity to evaporate and so settles on the metal surfaces in the space between the insulation and the equipment substrate, subsequently leading to corrosion. This type of corrosion is difficult to detect and test for without interrupting the day-to-day operation of midstream and downstream assets and will inevitably manifest in serious maintenance and safety issues. Although CUI is difficult to predict, it is possible to manage. Ineffective processes can potentially limit the lifecycle of the extremely expensive tanks, terminals and refining infrastructure that are essential to the global energy supply chain. Recognising and understanding what the triggers of CUI are helps to create precautionary measures to reduce the chances of it developing by putting suitable protective solutions in place. Prevention, as with all unseen threats, is the most suitable defence. This is where protective paints and coatings come in. Understanding CUI Operators in the process industries are aware of the potential damage that can occur in high heat and CUI environments. However, as an 'out-of-sight, out-of-mind' issue, CUI is often left unattended or unaddressed for too long, or in some instances, the wrong type of coating is selected in the first place or inadequately applied. It is therefore important for owners and operators of refining and storage assets to properly understand the influencing factors that contribute to CUI. They ought to work with their coatings manufacturer to explore the suitable products, review the testing and inspection procedures available to them, and develop a plan for ensuring cost-effective and timely routine maintenance. While CUI generally occurs in the temperature range between 50 – 175˚C, in high humidity and cryogenic environments corrosion can occur below this temperature – the so-called 'sweating pipe' syndrome. However, temperatures vary considerably across the constituent parts of each refinery, or adjoining processing and distribution infrastructure, and must be accounted for separately. This makes preventing CUI across an asset, and specifying a coatings solution to meet the precise needs of each piece of equipment, a challenging process. Furthermore, when specifying coating systems for new construction projects, protecting against CUI is just one of many coating considerations which require individual review. Assessing the treatment options When it comes to preventing CUI in oil, gas and petrochemical processing and storage facilities, there are three coating systems that are commonly used. These are epoxy/epoxy phenolic, thin film silicones and zinc silicates. Each has its own benefits, but there are also some limitations. Firstly, it is important to consider the relevant influencing chemical, environmental or operational factors that have the greatest impact on the effectiveness of coatings in tackling CUI. Epoxy/epoxy phenolic coating systems offer excellent performance when operating in the CUI temperature range, generally defined as being between 50 – 175˚C. However, when temperatures exceed this range, the coating is more likely to crack. This means water and moisture can get below the coating and directly onto the surface material, which is then susceptible to corrosion. Thin film silicone paints are based on silicone resins and are ideally suited to hot and dry conditions (up to 540˚C). Beyond these specific environmental conditions, such as during process cycling, the ability of thin film silicone paints to protect against corrosion is limited. Zinc silicate systems can also resist a wide temperature range – up to 400˚C. However, the drawback with this solution is that zinc silicates are 'sacrificial' in their defensive approach, and degrade rapidly when exposed to hot, wet CUI environments. Developing the right antidote These coatings – dependent upon the asset in question – are still suitable options for some equipment or installations. Following a rigorous R&D process, a new solution has been developed that should be considered. Versiline CUI 56990 has been specifically formulated to deliver optimal protection without the drawbacks and it is designed to provide better immunity under all environmental, operational and atmospheric conditions. The technology is a fibre-reinforced, single component, inert modified inorganic copolymer. It has been developed to provide better resistance to CUI as well as a unique resistance to micro-cracking, meaning less maintenance is required and assets are protected for longer and in a wider range of both Figure 1. Preventing CUI across an asset and specifying the right coating solution to meet the exact needs of each piece of equipment is a challenging process.

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