Using In-Line Inspection to Find Corrosion Under Insulation

Introduction

Corrosion under insulation (CUI) refers to the corrosive damage that takes place beneath insulation on piping and vessels due to water penetration and condensation from the dew point. It can cause varied and far-reaching problems, from loss of productivity to devastating accidents. However, CUI can be difficult to predict, access, and detect, and it requires substantial quantities of high-quality inspection data to get the complete integrity picture.

In most instances, pipeline corrosion takes place when an electrochemical reaction occurs, resulting in various forms of corrosion, such as pitting, uniform, galvanic, and crevice, and may be both localized and general. Areas of higher risk are pipe-support contact areas, welded features, low points, soil/air interfaces, and damaged insulation. Certain insulation types and designs also are at higher risk. Also, no matter how well the insulation is protected, dew points or lines that “sweat” can experience severe corrosion, even in arid environments.

The Challenges of CUI Detection

Many at-risk pipelines were constructed without taking accessibility for in-line inspection (ILI) into account. Therefore, historically, these pipelines have been inspected with external methods that may only provide a partial data set – if inspection is possible at all. For instance, these pipelines are frequently located under a dock, over water, at height, on a pipe bridge, or under a road crossing. Often, scaffolding, rope access, lifting equipment, or a combination of these methods is required for inspection. Another drawback is that removing and reinstalling the insulation is often necessary (and costly) for better external inspection results.

The Benefits of In-Line Inspection

Highly effective integrity management programs of such pipelines require thorough inspection data. Fortunately, there is an alternative – inspection from the inside. With no need to remove and reinstall insulation, ILI can detect, locate, and measure internal and external corrosion and reveal geometric damage such as deformation, denting, bulging, and ovality.

Because these pipelines were not designed with pigging in mind, one challenge is access (i.e., identifying potential access points). Access methods include removal of a blind flange, use of a flanged spool, removal of a valve and inserting a bend, modifying the pipe, and installing a temporary launcher and/or receiver. In addition, a compatible medium/fluid may be required to propel the ILI tool.