Reliable Sizing and Monitoring of Shallow Internal Corrosion in Pipelines

Internal corrosion, such as top-of-the-line corrosion (TOL) in wet gas lines due to condensation, constitutes a major risk to pipeline operation. Under certain circumstances, the internal corrosion growth rates can be as high as several millimetres per year.

Since internal corrosion is prevalent in all sorts of assets including off-shore and, notably, water pipelines, it is important that internal corrosion can be monitored and assessed even in challenging conditions.

Since the eddy current (EC) sensor technology incorporated in ROSEN’s shallow internal corrosion (SIC) tool can be used in bi-directional and robotic inspection tools, it is a suitable inspection method even in the presence of such challenges as high wall thickness, high product flow rates, tight geometrical constraints and in cases where the gas product prohibits ultrasonic technology (UT) measurements.

The SIC tool thus provides optimal corrosion growth monitoring in situations where inspection is difficult or impossible with conventional in-line inspection methods.
The EC coil systems of the SIC tool induce and detect currents in conducting materials, i.e. in the pipe wall.

Monitoring changes of these eddy currents enables highly accurate characterisation of surface metal loss defects. The EC sensors are especially sensitive to shallow features. This property distinguishes it from the MFL defect characterisation method which mainly reacts to volume changes, resulting from metal loss and is therefore more suitable for the detection of deeper features.

MFL is best suited for deeper and, generally, more substantial metal loss defects. However, it can be used within the optimal sizing spectrum of the EC inspection method. Conversely, because the EC inspection method provides maximum signal indication and better feature width sizing resolution, measurements taken with the SIC tool can assist MFL feature depth sizing algorithms in the MFL range.

This means that a combined use of the two technologies results in a significant improvement of the overall sizing capabilities.

ROSEN’s EC technology-based SIC tool is specifically designed to facilitate and optimise the process of monitoring shallow internal corrosion. As there is virtually no restriction to the type of tools that can be fitted with EC technology, it can be used even under exceptionally challenging conditions.

Due to its high lateral resolution of defect surface measurements, EC technology not only accurately distinguishes individual pits in dense clusters but detects and sizes even marginal corrosion features with great accuracy, thereby providing invaluable information on asset degradation.

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