Subsea technology - Corrosion monitoring

In the early 2000s, ClampOn developed the Corrosion-Erosion Monitor (CEM), a non-intrusive instrument for monitoring the wall thickness of pipes. Initially, through-thickness ultrasound was used, but this method required many measurements and was impractical for large areas. To address this, ClampOn explored acoustic guided Lamb waves, which use fewer transducers and provide greater area coverage. These waves are more tolerant of surface roughness and can detect changes in wall thickness by measuring phase changes in the signal.

ClampOn collaborated with scientific groups to refine this technology, focusing on the constant group velocity point of the fundamental flexural guided Lamb wave mode. This method was extensively tested in lab and field conditions, leading to the development of an industrial prototype. The first series of field instruments used piezoceramic transducers like those used for passive sensing and conventional ultrasonic thickness measurement. The pipe’s coating was removed at the contact point between the transducers and the pipe wall, and the transducers were installed with clamping brackets. A high-strength adhesive was used as a permanent acoustic couplant between the transducers and the pipe wall.

Long-term testing led to concerns that both the piezoceramic transducers and the adhesive couplant would change over time. In addition, the need to remove coating, and to clean, apply adhesive, and re-seal the external pipe surface was considered too complicated. This concern prompted a search for alternative transducer technologies and led to the successful adoption of electromagnetic acoustic transducers (EMATs). EMATs operate without mechanical oscillations, eliminating the need for acoustic coupling, and can be installed on coated surfaces. A specially designed EMAT was developed to enhance the transmission and reception of the fundamental, flexural guided-wave mode. This had the added advantage of very high phase measurement stability over time.

New electronics were required for EMATs, resulting in the development of two generations of “CEMAT” platforms. The subsea version can operate up to 16 transducers and is self-contained, while the topside version can handle up to 32 transducers in hazardous locations. These systems continuously monitor wall thickness and log the data, which can then be processed to create wall thickness maps using CorrPRINT tomography software. CorrPRINT can supplement or replace the instrument output with key data, such as the thicknesses and positions of wall thickness minima. 

The ClampOn CEM and the CorrPRINT software are scalable, allowing for both small and large setups, and can provide detailed monitoring data from multiple wave-propagation paths. This data is processed to generate wall thickness maps and key values for integration into Supervisory Control and Data Acquisition (SCADA) systems.

You can read more about the history of the development of the ClampOn CEM here: https://worldoil.com/news/2024/10/24/subsea-technology-corrosion-monitoring-from-failure-to-success/.