The tubing of heat exchangers can be inspected with a number of various NDT techniques. Heat exchangers are considered critical parts within process installations; a failure often leads to unexpected breakdown and resulting downtime induces substantial costs.
For Tube Inspection, Mistras provides the following techniques; Eddy-Current, IRIS and visual inspection. These NDT techniques provide the asset owner information about overall condition and operational integrity of the tubes. The inspection results are the basis for maintenance plans, critical tubes can be repaired immediately.
Visual Inspection provides the utmost insight of the overall condition of the heat exchanger. Both tubes and tube sheet are examined and every relevant abnormality will be documented and reported to the asset owner. Visual inspection often includes use of video endoscope.
Eddy-Current testing is most commonly used for inspection of heat exchangers. It is an electro-magnetic based technique, applicable to conductive materials. Depending on the type of tube and/or potential defect mechanism the following methods can be used;
- Standard eddy-current
- Partial saturation eddy-current
IRIS (Internal Rotary Inspection Service)
The IRIS technique is applied to assess the wall thickness of heat exchanger tubes. An ultrasonic probe with a mirror is inserted into a tube filled with water. The probe transmits ultrasonic waves onto the mirror and deflects the signal onto the inner tube surface. The signal reflects back again via the mirror to the transducer. Fast rotating of the mirror gives real measured data displayed in a c-scan. By pulling the probe out of the tube, a full scan can be done with wall thickness values. IRIS allows assessing ID and OD volumetric defects.