Corrosion Under Insulation (CUI) typically occurs on thermally insulated pipes. A systematic approach is needed to minimize the risk of CUI, and part of this approach is to choose coatings that protect the pipe from corrosion and can resist the often aggressive environment with insulated pipes. Presented is an innovative thermoplastic type of coating material for CUI purposes that can be used for both newly constructed pipes and coating repair. Presented are the technical assessments that were carried out to evaluate performance under CUI conditions, including tests as specified in various industry standards like ISO 21809-31 (e.g. accelerated ageing tests), ISO 12944-92 (corrosion at scribe), and additional customized tests including resistance to hot dry/wet cycling including thermal shock, and freeze/thaw cycling. Furthermore, a study was conducted to determine the capabilities of arresting pit growth in stainless steel. From these test it was concluded that these type of coatings are potentially suited for use in CUI service conditions up to temperatures of 120°C.
An innovative thermoplastic type of coating material based on pure isobutene homopolymer was investigated to determine whether it would be fit for purpose in CUI services at low and moderate temperatures up to 120 °C. This polymer is commonly called Polyisobutene (PIB) and has a unique set of properties that are beneficial for protecting metallic structures from corrosion. Polyisobutene is a polyolefin with a chemical structure similar to Polyethylene (PE) and Polypropylene (PP). One of the major differences is that PE and PP are solid materials with a high degree of crystallinity, whereas PIB does not have a crystallization or melting temperature. PIB has a glass transition temperature (Tg) below — 60 °C which indicates that the polymer is a liquid above this temperature. Due to this liquid nature, mechanical stresses that for example occur with expansion and contraction upon temperature fluctuations will not accumulate in the coating. Adhesion of coatings based on PIB are solely based on van der Waals intermolecular forces. To obtain good adhesion the surface preparation of the substrates is not as critical as with many other types of coatings. They have good adhesion to various substrates like carbon steel, stainless steel, and existing coatings like liquid epoxies. PIB also has a low permeability for water vapor and oxygen, which is favorable for protection against corrosion.