Insulate against corrosion with Corrosion Under Insulation Coatings
Corrosion Under Insulation (CUI) is the insidious problem causing billions of Rand in damage and loss every single year. It is of grave concern to facility owners, plant operators, engineers, and workers across industry, from oil and gas to chemical and other process industries. It is estimated that up to 60% of pipe failures are caused by CUI, and without maintenance and vigilance the problem will lead to shutdowns, repairs, accidents, downtime production loss, environmental damage, and more. The causes behind CUI are well documented and understood, but preventing it has proved a more difficult task.
In this article we explore the causes of CUI and one of the most effective ways to prevent it with insulation coatings. We also look at the top insulation coating products and manufacturers in South Africa.
The causes of corrosion under insulation
Corrosion under insulation is the name given to any type of corrosion (galvanic, acidic, alkaline, or chloride) that occurs when moisture builds up on the external surface of insulated equipment such as pipework but also vessels and tanks. The water could be rain, leakage, sweating, or another water source but the end result is the same – the trapped moisture causes rapid corrosion and costly problems. Some of the most common contributing factors to CUI are:
The environment and climate can affect CUI in a number of ways. Breaks in the weatherproofing or leaks are more dangerous in areas with higher rainfall, and high humidity can lead to condensation (the ‘sweating’ pipe syndrome). The ambient temperature is especially important where temperatures cycle above and below the dew point. This causes a wet and cold/dry and hot cycle where condensation forms and is then baked off. The interim period of warm and damp leads to high corrosion rates. Then of course there are the added dangers of marine environments for salt contamination. And it isn’t just the weather that can break in – steam, spillage, sprinklers, wash cycles, all of these can penetrate the insulation barrier.
- Service temperature
The temperature susceptibility range for CUI is between -4°C and 149°C, and this range increases or changes depending on the substrate. Though continuous operating temperatures above or below this range may appear to place surfaces out of risk, other factors can still lead to the development of CUI. Thermal cycling is a particular risk for CUI as it forms condensation.
- Insulation type
CUI of carbon steel is possible under all types of insulation but in some cases the insulation itself can accelerate or even contribute to the problem. Some insulation materials contain salts or compounds which corrode or create a corrosive environment in the presence of water. If the insulation retains water, or allows it to permeate the material, this can also create corrosive conditions.
Insulation coatings are only as good as their application
However carefully insulation may be installed, the risk of CUI is still present. Using thermal insulation coatings or CUI coatings as a preventative measure has emerged as one of the best methods of combating CUI, in combination with a thorough maintenance programme. The highly adhesive and resistant nature of these coatings provides an added barrier to moisture and corrosive compounds and protects the substrate moisture buildup and leaks.
There are a range of chemistries used as CUI coatings, including epoxy phenolic, epoxy novolac, silicone hybrids, inert multipolymeric matrix coatings (IMM coatings or inorganic ceramic coatings), and inorganic zinc. The choice of coating is not, however, a simple case of choosing ‘the best’ CUI coating. All the relevant factors and conditions need to be taken into account to find the right CUI coating for the specific application. Temperature ranges, thermal cycling, environment, climate, downtime, substrate type and more need to be factored in.
Modified epoxies to IMM coatings – A guide to CUI coatings
Given the broad range of conditions and environments under which CUI occurs, there is also a wide range of CUI coatings. When choosing a CUI coating it is important to ensure that it:
- Is compatible with the substrate and is highly adhesive
- Is compatible with maintenance and application requirements
- Withstands process temperatures, particularly the corrosion danger zones for the substrate
- Withstands the exposure scenario – immersion, thermal shock, cyclic, steam-out etc.
- Resists variable pH environments, chemical exposure, chlorides, halides, and sulfides
Below is a comparison of some of the most commonly used CUI coatings and the properties they exhibit (from NACE).
|Properties||IMM Coating||High Build Silicone||Aluminium-filled High Build Silicone||Inorganic Zinc||Novolac/ Phenolic Epoxy|
|Max. continuous operating temp.||540°C||540°C||400°C||400°C||200°C|
|Suitable for cyclic hot/cryogenic service||Yes||Yes||Yes||No||Yes|
|Can be applied to hot surface||Yes (up to 316°C)||Yes (up to 232°C)||Yes (up to 120°C)||No||Yes (up to 150°C)|
|Recoatable with self||Yes||Yes||Yes||No||Yes|
|Max. DFT per coat||125-150 microns (2 coats)||100-125 microns (2 coats)||200 microns||75 microns||125-200 microns (2 coats)|
|Air dries to hard film||No||No||No||Yes||Yes|
|Suitable for Stainless Steel||Yes||Yes||Yes||No||No|
CUI coating manufacturers and products in South Africa
There are a number of CUI coatings manufacturers operating in South Africa, including AkzoNobel, PPG, Hempel, Jotun, and more. Below we look at the CUI coatings they produce and the benefits and applications of each. No matter the requirements, there is a coating to suit your needs. AkzoNobel in particular have produced the “Universal Pipe Coatings” (Interbond 2340UPC and Interbond 1202UPC), designed specifically for simplifying process pipework and OEM coatings specifications. They standardise and simplify coating specifications by providing a single coating for a range of end uses. Coating manufacturers are dedicating themselves to solving corrosion under insulation.
The best coating applications are part of a system, and CUI coatings are no different. If you are having difficulties with corrosion under insulation, or would like to set up your facility with the best protection possible, get in touch! Our experts are here to help. We will connect you and your project with the right coating specialist and product to meet your specifications. Simply click the “Request a Quote” link beneath this article and tell us about your project and its requirements to get started.
|CUI Coating||Coating Type||Desciption||Suitable End Uses|
|Interbond 2340UPC||Two component epoxy phenolic coating for high temperatures||Delivers corrosion under insulation protection for temperatures from -196°C to 230°C. It has excellent tolerance to over-application and forms a hard, damage resistant film. It cures in low temperatures down to -5°C with short minimum overcoating intervals.||Carbon steel, stainless steel, insulated equipment, uninsulated equipment|
|Interbond 1202UPC||Two component, ambient cure, inert multipolymeric matrix coating||Delivers corrosion under insulation protection for temperatures from -196ºC up to 650ºC. It is compliant with the performance criteria of the ISO12944-9 standard, without a primer. It has short minimum overcoating intervals and is crack resistant during transit.||Carbon steel, stainless steel, insulated equipment, uninsulated equipment|
|Jotatemp 1000 Ceramic||Two component titanium catalyzed inorganic ceramic copolymer||Resistant to continuous temperatures down to -196°C and up to 1000°C. On carbon steel substrates it can be used at up to 650°C continuously and 750°C peak. It can be applied on hot substrates up to 250°C. Ambient cure.||Carbon steel, ceramic substrates, insulated and non-insulated surfaces|
|PPG Hi-Temp 900||Two-component, ambient cured multi-polymeric heat resistant primer/coat||Cyclic temperature resistance from -196°C to 320°C and continuous dry temperature resistance from -196°C to 482°C. Resistant to thermal shock / cycling and intermittent immersion and boiling water. Scratch and mar resistant coating for ease of transport. Formulated to prevent chloride induced stress corrosion cracking of austenitic and duplex stainless steel. Good UV resistance.||Carbon steel and stainless steel in new build applications|
|PPG Hi-Temp 1027||One component, high build, heat resistant, inert multipolymeric matrix / inorganic ceramic coating||Continuous temperature resistance to 650°C with intermittent temp. resistance to 760°C. Cyclic temp. resistance from -196°C to 540°C. Ideal for hot and cryogenic service. Can be applied directly to hot surfaces (up to 316°C). Prevents chloride-induced external stress corrosion cracking of insulated austenitic stainless steel. UV stable.||Carbon steel, stainless steel, insulated equipment, uninsulated equipment|