Pulsed Eddy Current Technology for Corrosion Under InsulationLaura Nelson
When Corrosion Under Insulation (CUI) occurs, it can lead to a loss of primary containment and possible environmental contamination. Unfortunately, the insulation used to optimise the thermal efficiency of the processes involved also makes it extremely difficult to locate the corrosion. In some cases, it may require the shutdown of the process but in all cases it will require the removal of the insulation to look for CUI. Most of the time, this is avoidable if a Pulsed Eddy Current inspection tool is used.
A powerful tool for detecting CUI through the insulation, is Pulsed Eddy Current Technology (PECT).
PECT measures the decay time of the eddy current induced in the carbon steel object under examination during pulsing. The decay time is proportional to the volume of material under an area called “footprint”. The time of each reading is compared with the time of the “reference point”. Because during the inspection the footprint area stays fairly constant, comparing the volumes is the same as comparing the wall thicknesses.
The main advantage of PECT is as a screening tool: it gives information about the status of the object(s) in order to isolate the areas of interest on which to perform a standard NDT survey.
Standard inspection techniques require insulation removal if applied from the outside; or shut down and clean a confined space for personnel entry if applied from the inside, both of which are far more costly in comparison with PECT. Other benefits of the system include:
- Faster inspection time
- Wider coverage
- Locate weld locations whilst insulation is in place
- In-service Inspection
- Scan through up to 250mm of insulation
- Repeatable and reliable results
- Easier analysis thanks to simpler scan patterns
- High speed testing at high insulation/ lift-off distance