Testing corrosion under insulation

Corrosion under insulation is a major risk factor in Oil&Gas producing facilities. Most pipelines and process equipment containing hydrocarbons are made of various grades of steel. All steel types are to some extend prone to corrosion if the right environment develops. Carbon steel is the most common material used in pipelines and will need surface protection in order to prevent corrosion reducing the pipe wall thickness over time.

The development of corrosion under insulation (CUI) on pipelines is particular dangerous due to the simple fact that it’s not visible and can’t be detected/monitored by visual inspections. Corrosion that is allowed to develop over years, may eventually lead to cracks or defects in the pipe or process equipment, resulting in release of hydrocarbons and the risk of catastrophic fires. The process of corrosion development on pipelines and other process equipment is dependent on many factors. It’s therefore of outmost importance to understand how different insulation materials interact together and effect the contributing factors for CUI.

Corrosion on steel is almost always depending on the presence of water. Furthermore, for corrosion to occur at the steel surface water must be
 present in its free liquid form, in order for the electrochemical corrosion mechanisms to take place. Traditional protection against corrosion is therefore typically based on several coating layers, with a suitable surface coating as the primary protection. However, since the surface coating might be scratched or damaged by other mechanical impacts, the second layer of CUI protection is keeping the water away from the pipe surface. On pipelines and process equipment covered with insulation, this is typically done by installing a water proof cladding over the insulation. Furthermore, some insulation materials also depend on the water proofing to avoid absorption of large amounts of water and the associated reduction of their thermal insulating capacity.

Water proof cladding or other outer weather barriers are only effective when they are 100% intact, and installed without errors. It’s a common proverb that water proof means that water can’t get out, it will always get in! It’s therefore important to understand what happens when the protection mechanisms fails. The test procedures and standards used for evaluating CUI vary extensively between various vendors of coating materials and insulation materials, and are often intended to show how a particular product performs under a set of conditions, often favorable to the product. Unfortunately, few of these tests consider the effect the combining multiple materials, and the effect of enclosing the insulation system in a water proof weather cladding. As an example, a hydroscopic material with good vapor permeability will have excellent results in a CUI trail without external weather proofing when water is allowed to dry out. However, if the external weather protection “capture” any present water and the insulation is not allowed to dry out, the resulting corrosion can be quite severe.

Benarx has therefor developed its own CUI test set-up to better understand how materials and protection mechanisms act together. The test set-up is based on 10 parallel test tubes filled with water kept either at a constant temperature or temperature cycled. Each pipe is covered with a complete insulation system and 5 liters of saltwater (3,5 wt% NaCl) is introduced every week into the top of the insulation and allowed drain out on the other end of the pipe.

These tests has provided new test results that are somewhat contradictory to some of the conclusions given by other test results published in the industry, and has enabled Benarx Solutions in our dedication to be a solutions provider, and to work out more effective methods for protecting against CUI. We believe that our long experience with real life systems, combined with the development of new solutions based on simulation and testing programs, is contributing to bringing the insulation industry forward.