Third Generation Polysiloxane (TGPS) ambient curing CUI mitigation coatings have been used in the petrochemical industry for over five years. These coating technologies have demonstrated positive results in both shop and field application for asset management in elevated temperature, cryogenic and cyclic applications across -196 to 650° C/-321 to 750° F operational temperatures. TGPS coatings have demonstrated effective use of a two-step (primer-insulation) CUI mitigation coating approach operating up to 400° C/750° F, when compared to the traditional (CUI coating-fibrous insulation-cladding) systems.
Corrosion Under Insulation (CUI) is a well-known industrial problem that has been plaguing asset owners for decades. CUI presents one of the costliest corrosion factors for Oil and Gas, petrochemical and general processing industries and can result in unplanned shutdowns, maintenance repairs or even explosions on live plants
The traditional CUI prevention concept is composed of a three-component system:
1. Steel – substrate for processing chemicals (constant or in cyclic temperature operation)
2. Insulation – provides thermal efficiency
3. Cladding – protection for insulation and steel from atmospheric elements
In practice the cladding system does not truly seal from the atmospheric elements. Rain, deluge water, steam or cooling towersoverspray is often is able to penetrate the system through an ingress point in the cladding material, generally where complex structures pose huge difficultly in building a watertight system. Additionally, when permeable insulation (open cell) is used, condensation may also be a CUI contributor.
Once water has penetrated an insulated system via ingress points such as breaks, seams, gaps, or unsealed valve sections, it can attach the CUI coating to cause corrosion to the steel. Potential contaminants like acid, high salt content rain or leaching chemicals from the plant environment or leachate from insulation systems that can form reactive compounds accelerating the corrosion rate.
Generally, usage and specification of CUI coatings is dependent on operating temperatures of processing equipment. NACE SP0198 -2017 "The Control of Corrosion Under Thermal Insulation and Fireproofing Materials - A Systems Approach" is an industry standard for CUI coating classifications. Highlighting and tabulating substrate (carbon or austenitic/duplex stainless steels) material, temperature ranges, recommended surface preparation, surface profile (Rz) and coating dry film thicknesses of CUI protective coating systems.