THE IMPORTANCE OF PAINT SYSTEMS UNDER INSULATION AND FIREPROOFING

Based on old practises in oil & gas process plants no paint system was considered under insulated piping or equipment. It was believed that no condensation is fomrmed under insulated surfaces and therefore no need to be protected.

Nowadays, it is a well-known practice that corrosion under insulation and fireproofing, briefly known as CUI, is a detrimental threat in all process plants and some standard design specifications shall be fully followed to avoid possible corrosion failures.

As a main design practise in this area, NACE SP-0198 - 2017 shall be followed. The new revision includes many design tips related to insulation. Some tipes are related to periodical inspection and some others are related to considering protective coating under insulation. Some brief tips related to paint systems mentioned in SP-0198 are outlined hereunder:

• Field experience has shown many instances of CUI on equipment and piping operating at temperatures up to 175 °C (350 °F), and it has been recognized within industry that carbon steel operating with a skin temperature in the temperature range of –4 °C (25 °F) to 175 °C (350 °F) has the greatest likelihood of CUI. So, all insulagted piping and equipment operating in the range of –4 °C (25 °F) to 175 °C (350 °F) ought to be painted.
• Inorganic zinc-rich coating shall not be used by itself under thermal insulation in the 50 to 175 °C (120 to 350 °F) service temperature. Zinc provides inadequate corrosion resistance in closed, some times wet, environments.
• As a proposed paint system Phenolic Epoxy in two layers of 100-150 micron is a proven choice mostly utilized by different practices and it is proved as a protective masure.