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Selection of Coating Systems for CUI Service Christian Zupicich, Technical Service, christianz@hitempcoatings.com Michael F. MeLampy, Vice President, mmelampy@hitempcoatings.com Hi-Temp Coatings Technology, Inc., P. O. Box 2347, Acton, MA, 01720, USA ABSTRACT This paper will discuss issues related to corrosion protection of high temperature carbon steel substrates which are insulated to preserve energy, provide process control and to keep workers safe from burn injuries. Corrosion under insulat
    Selection of Coating Systems for CUI Service Christian Zupicich, Technical Service, christianz@hitempcoatings.com Michael F. MeLampy, Vice President, mmelampy@hitempcoatings.com Hi-Temp Coatings Technology, Inc., P. O. Box 2347, Acton, MA, 01720, USA  ABSTRACT This paper will discuss issues related to corrosion protection of high temperature carbon steel substrates which are insulated to preserve energy, provide process control and to keep workers safe from burn injuries. Corrosion under insulation (CUI) is a serious problem for many owners who have insulated service, where severe corrosion often occurs which can cause plant or process shutdowns, environmental damages and potential injuries to workers.  A review of past and current technologies for preventing CUI will be presented. The initial and long term costs, performance characteristics, expected service life as well as ease of application and repair of coatings used under insulation will be discussed. Field and laboratory performance experience obtained from users, third-party laboratories, and vendors of the various coating systems are used for this comparison. It is this long term cost which determines the true value to the user of any CUI coating system. Local and overall risks associated with perforations are also of major concern. The two along with several other factors are important in coating selection process. INTRODUCTION Corrosion Under Insulation (CUI) is a problem for those involved in power, refining, petrochemical and other thermal processing industries. CUI is corrosion that occurs at the substrate beneath an insulating material which can develop and progress quickly dependent on the availability moisture, contaminants and temperatures. All of this happens where it is hidden from view and is often overlooked.  A specification manager of a major oil and gas multi-national ,  stated: “The REASON the steel was not adequately protected in the first place is because when our plants were built, industry did not understand that the environment under insulation was going to be almost like immersion conditions (or worse) so the correct type of coating was not used. As a result, almost NONE of the surfaces under insulation, in facilities older than 15 years, are adequately protected from CUI. CUI is a phenomenon because of our ignorance.” Insulation is applied on pipes and vessels which contain and/or transfer hot materials to provide heat retention or energy savings, to improve process control, and/or to protect workers who access the equipment with protection from burns. Refining, petrochemical processing, power generation and other process generally involve heating or hot fluids and gases    transmission to produce to create intermediate products or end products. Power plants often use steam and high pressure steam to create electricity. Cladding, typically galvanized steel, aluminum, stainless, or plastic based is attached over the insulation to protect it from damages and to help keep the insulation materials dry. These cladding systems can deteriorate over time and can fall into a state of disrepair  Additionally improper construction may allow water leakage into the insulation layer and to the substrate. Often this water contains electrolytes. Potential microenvironments can be created within the insulated jacket and as a result corrosion can begin, in places more concentrated, resulting in accelerated corrosion leading to potential mechanical failures such as leakage or worse. COATING SYSTEM SELECTION NACE Publication 6H189, from 1986 “A State of the Art Report of Protective Coatings for Carbon Steel and Austenitic Stainless Steel Surfaces Under Thermal Insulation and Cementitious Fireproofing” (1) , states the following: “No particular corrosion problems were considered or anticipated with carbon steel under thermal insulation when the plant construction boom began in the 1960s. Prior to that time, insulation was applied over bare steel, or in some cases, over one coat of oil-base primer that had been applied over mill scale. When serious corrosion was later noted, many engineers concluded that better surface preparation and a better primer, or better maintenance of the insulation waterproofing, would mitigate the formation of corrosion.”  After finding extensive corrosion hidden in these insulated environments, the addition of coating systems for use under insulation became more common. However, coating system selection has been a learning process. Coating types included; inorganic zinc, elevated temperature coal tar epoxies, phenolic and novolac epoxy tank linings, thin film silicones, and thermal spray aluminum. A great deal has been learned as a result of these systems coming into disrepair, and newer technologies have been developed to allow engineers with greater options for application methods and service life resulting in new first and life cycle cost considerations for selecting coating systems to work in these harsh environments. Currently there are no universally accepted test methods for use in CUI coating selection. Several manufacturers have developed test procedures, which should be evaluated by the specifier and end user for relevance to their operations. With no accepted test methods the specifier and owner should evaluate the look to the properties of the coating, including the temperature resistance, ability to resist thermal shock, thermal cycling, and boiling water, as well as constructability and user friendliness, to develop an understanding of the applied products lifecycle and cost to determine which will be best for the CUI service. All CUI service requirements may be different resulting from different environments, insulation and cladding systems, maintenance efforts of the facility and of course actual operating environments including the possible need to steam clean, or purge pipelines and vessels as part of an operating units regular maintenances.  As there are limited accepted test methods some owners have developed their own testing mechanisms and suppliers are also pushing forward accelerated testing mechanisms to help predict the life of CUI coatings. New technologies for testing and coatings formulation are beginning to show promise in determining the best way forward.    Where to start in finding and repairing CUI: One major multinational oil and gas refining company spent over two years using Risk Based Identification models and utilizing many testing methods to help determine where to start planning and begin to repair equipment with CUI. A ten year program was then begun to repair, recoat, and reinsulate equipment, vessels and pipelines so that they can continue to operate for many more years. and is currently doing maintenance and repair as a part of a ten year program. Other owners are following this course of action and many more will need to moving forward. If not the operating units who prefer to ignore the mounting evidence will do so at their own peril and risk. INSULATION and CLADDING Improvements in insulation and cladding technology have been made steadily since the mid 1980’s. It is important to know that eventually most if not all cladding systems will leak. This leakage allows water and contaminants (electrolytes) to enter the clad insulation system, where it can then become trapped, and with moisture evaporation these contaminants can concentrate. The configuration of the insulation and cladding system over vessels and related piping can allow this moisture and moisture vapor to travel quite far, resulting in corrosion in unexpected places. Insulation systems can include, foam glass, calcium silicate, expanded perlite, mineral wool, and fiberglass. Newer insulating materials include aerogels and spray applied ceramic loaded acrylic coatings systems. Insulation systems are typically attached using mechanical means, while some spray applied insulations are adherent to the surface. Mechanically fastened insulation materials are then generally clad with sheet metal to protect the insulation from damage and to stop the flow of water from entering into the insulation material, while the spray applied materials may need to be top or seal coated. The mechanical attachment of the insulation is appropriate in higher traffic areas, however these mechanical attachments lead to breaks in the insulation, resulting in heat loss, potential formation of crevice corrosion where the insulation is compressed tightly against the substrate, and other issues. CORROSION CONTROL The following could be thought of a as a basic definition for a good elevated temperature or CUI coating. A coating for elevated temperature and/or CUI service must be easy to use in both new construction and maintenance and repair situations, survive elevated temperature, thermal shock and thermal cycling, boiling water, intermittent immersion, and still be able to provide long term corrosion protection when a corrosion cell develops. Corrosion control coatings are not always used under insulation. Even though many processes are thought to be isothermal or continuous, all processes are cyclic - over time. Use of protective coatings is good decision for the life of the project especially when repair and maintenance can be so expensive in the future. Without a well thought out plan with appropriately selected corrosion control coatings, and when left unchecked, this corrosion can result in process fluid leaks through perforations. These perforations can result in unplanned shutdowns, and when hydrocarbons are involved, can result in fires and explosions leading to    extensive down time, repair costs, environmental remediation, process unit down time, personnel injury and even death. Owners desire cost-effective long life protective coating systems. Each unit and process is unique and needs specific coating system solutions that result in the best applied and lifecycle project costs. The economics of repair and maintenance are driven mostly by the cost of down time during which repairs and equipment replacement can be made, other costs include labor, access, and materials. Outages are scheduled in advance and often include coating replacement projects, with many painting workers on the site. Of course the huge cost of a shut down – even just the lost profit from operations can be quite large and as a result outage time frames are minimized. CONSTRUCTION ISSUES The size and scope of maintenance efforts, plant expansions, and upgrades continues to grow. For new construction the coating system must survive transportation to the final site, installation, and assembly. Touch up in the field is expected and must be quick and easy to accomplish. Maintenance and upgrades in existing units have many constraints and limiting factors involved when trying to do proper coating application. Most plant turnarounds have become too brief, intense and crowded. Inaccessible areas are also a big concern. Additionally, these projects involve health safety & environmental issues. Shutting down a facility for maintenance, results in lost revenue and related profit which cannot be made up or replaced as many of these operations are continuous in nature. Just lost profit can amount to a large sum of money every day, and is one of the largest costs encountered by an operating facility. As such maximum cost effectiveness maybe achieved by performing as much maintenance as possible while the facilities are in operation, allowing the owner to continue revenue and profit generation. Several years ago a managing director of a venture in China asked (paraphrased) the following question: “Why can I only do coating maintenance work during an outage? I have a 1000 guys running around here changing valves, motors and pumps, and then I have to have another 1000 trying to paint everything. Surface preparation and coating work is not realistic to do when performing maintenance on all the mechanical equipment, and it can only extend the outage!” This manager understands the true cost of outages and why they can be so costly. Not only do you lose revenue and related profits, each day of outage work is very costly especially with coatings work. With larger than normal crews, quality of application may become suspect. Pre-Construction Inspection Issues  An important requirement in planning coating work for insulated service, in or out of service, is to determine the actual peak surface temperature of operating equipment. Knowing the design operating temperature is important but it is the peak temperature that may damage the applied coating material. Many operators may use high pressure steam to de-sludge operating vessels and related pipelines raising the temperatures of the substrate higher than design temperature. Often this “unplanned” peak temperature may be detrimental to a coating
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