Comparison of insulation materials and their roles on corrosion under insulation

Abstract

Thermal insulation is used in petrochemical and refinery plants where pressure vessels and piping system are insulated to conserve energy. Over time, water enters into the insulation through various pathways and is entrapped at the steel surface leading to corrosion under insulation (CUI). Mineral wool is one of the most used thermal insulation even though it is prone to absorbs water and causes CUI. A water repellent insulation can be an alternative thermal insulation to prevent CUI. However, limited research has been done in the public domain. Therefore, the present study investigates and compares the roles and influences of mineral wool and a water repellent insulations on CUI. In addition, the presence of drain holes and its ability to reduce CUI was evaluated. The susceptibility to CUI of carbon steel was investigated at 80 °C using a newly developed test rig in a controlled environment (25 °C and 50 %RH). An electrochemical impedance spectroscopy technique was used to monitor the rate of insulation dry-out. Due to localized nature of CUI, a 3D light microscope was used to analyze the surface profile of the samples after exposure to CUI. The results has emphasized the correlation between the wet time and severity of CUI.