51316-7804-Evaluation of Protective Coatings to Mitigate Corrosion under Insulation

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Product Number: 51316-7804-SG

ISBN: 7804 2016 CP

Author: Yang Yang

Publication Date: 2016

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Corrosion under insulation (CUI) is caused by direct contact of metal surface with water accumulated within the insulation. It is a common external corrosion issue experienced both onshore and offshore including the Gulf of Mexico.Insulation is required on equipment for two main reasons; (i) for personnel protection due to the high temperatures (>160 °F) and (ii) for heat conservation for process control.For Personnel protection besides using specialized fabricated barrier cages installed around equipment insulative coating systems are used. When an insulative coating is applied shut-in of equipment is not typically required. There are different application temperature limits for different insulative coatings. This prevents deferred production losses in most cases.For heat conservation for process control the main choice has been the use of traditional and typical insulation material. For example in the past mineral wool was used but over time insulation with lower moisture permeability are being used but still do allow some moisture through to the equipment metal surface particularly at insulation damaged areas and termination points. When traditional typical insulation is applied the equipment is preferred to be shut down by facility managers or applied before service at ambient conditions.For both situations mentioned above i.e. the use of (i) Insulative coating systems and the use of (ii) traditional typical insulation a protective coating system is required under the insulating material. Based on different requirements during insulation application the protective coatings need to be applied either in the hot service conditions or at ambient conditions.A laboratory testing program was developed and the objective was to evaluate and rank different protective coatings that can be applied to mitigate CUI under each type of insulation. Coating systems tested were applied on hot substrate as well as on ambient substrates. The testing program was conducted in two stages; a screening stage to short list products and then more detailed testing on the short listed products. Thermal stability test hot water immersion test and cyclic corrosion test were performed on steel samples coated with different coatings. The results showed that different coating systems performed differently as expected and some were screened out and the others that passed the screening were ranked. Details such as coating application testing procedures and testing results are discussed in this paper.