The problem of corrosion under insulation
Recently we discussed the basics of high temp coatings. These coatings are often used in process facilities such as refineries, oil and gas, and petrochemical plants. One of the main uses of high temp coatings in these facilities is for the protection of pipe systems that regularly transport various materials at high heat.
In order to increase efficiency, reduce heat loss and capitalize on energy savings, these hot pipes are usually covered with a layer of insulation. This insulation is also sometimes put in place to protect personnel from being burned by these pipes. Unfortunately, it is this layer of insulation that helps to create the conditions for one of the most vexing corrosion problems in the industry, known as corrosion under insulation, or CUI.
Why it happens
CUI occurs when moisture becomes trapped in the area between the hot pipe and the thick layer of insulation surrounding it. Since this moisture is unable to escape, prolonged contact between it and the steel substrate accelerates corrosion. Whether it enters through cracks or holes in the insulation, this trapped moisture has the potential to cause rapid rusting and corrosion on the pipe’s surface.
Since the layer of insulation completely surrounds the pipe, corrosion under insulation often goes unnoticed. When the insulation is finally stripped from the pipe, either to investigate a problem or as part of a scheduled replacement, facility managers sometimes find the pipe to be completely ruined.
What to do
Because of this risk of accelerated CUI, great care is taken to make sure that the insulation surrounding a pipe is completely enclosed. Joints, terminations and other irregularities along the length of the pipe are carefully sealed. Nevertheless, moisture does penetrate insulating layers with some frequency. As a result, CUI has become something of a hot topic in process facilities. Facility managers are constantly on the lookout for the magic bullet that will eliminate the problem of CUI.
As of now, no magic solution exists for the problem of CUI. The best plan for battling the problem entails checking piping under insulation often as a part of a scheduled coatings maintenance plan, sealing insulation with care, and most importantly, choosing a high quality high temp coating.
It’s important to verify that the high temp coating you choose has been specifically designed to stand up to high temperatures and to defend against CUI. Also, that it is designed to withstand the range of temperatures the substrate will subject it to. When chosen to match these criteria, high temp coatings are the most effective method for fighting CUI currently available in process facilities.