Advancements in CUI Detection and Overview of MsS Guided Wave

Introduction

Corrosion is a leading cause of asset failure in the oil and gas industry. Over time, undetected corrosion degradation can cause an asset to fail before its projected lifespan, resulting in a costly repair or replacement, unplanned downtime, and lost revenue. Beyond the financial hits, undetected degradation can also lead to critical safety risks. Thus, to effectively manage mechanical integrity, organizations need reliable methods of identifying the current states of corrosion occurring within their assets. Therefore, effective inspection planning and monitoring of assets is essential to maintaining mechanical integrity.

Corrosion Under Insulation

Corrosion under insulation (CUI) is a severe form of localized external corrosion that occurs in carbon and low alloy steel piping and equipment that has been insulated. This form of corrosion occurs when water is absorbed by or collected within the insulation. In these circumstances, corrosion occurs as the base material is exposed to water and oxygen. CUI commonly appears in temperatures ranging between 32°F and 300°F. Acceleration of CUI can be caused by cyclic thermal operation, intermittent service, and equipment design.

Common occurrences of CUI include the following:

• General and pitting corrosion of carbon steel, which may occur if wet insulation comes into contact with carbon steel—particularly if acidic product can leach material from the insulation.
• External stress corrosion cracking (ESCC) of austenitic stainless steel, which is a specific type of corrosion mainly caused by the action of water-soluble chlorides from rainwater or insulation that does not meet material standards.