Failure Analysis of Heat Exchanger Using Eddy Current Testing (ECT)

Shell and tube heat exchangers are widely used in the oil and gas, petrochemical and nuclear power sectors. The most important aspect of the turnaround is the routine testing and inspection of the in-service heat exchanger. Heat exchangers in use are the primary cause of tube flaws such as pitting, corrosion, erosion, fretting corrosion, crevice corrosion, stress corrosion cracking, wear, galvanic corrosion, fatigue cracking, microbiologically influenced corrosion, and so forth. For research, a seamless nickel-iron-chromium alloy-tubed SB 163 (UNS 8810) heat exchanger was taken. The total number of tubes that need to be inspected is 286 tubes with a specification of 19.05 mm OD x 2.11 mm thickness x 5000 mm length. From the different advanced NDT techniques, the eddy current testing (ECT) was chosen for inspection since it has become one of the most popular NDT methods for locating discontinuities in heat exchanger tubes. A standard calibration tube was used to calibrate the system's response and set the sensitivity. During the inspection, the ECT probe was inserted from the below side up to the other end and collected while pulling the probe from the tube. Inspection data were recorded for the length of each tube. All indications were assessed, and defects were categorized as different extents of wall thickness loss after inspection. The inspection report shows how many tubes were found defective and need to be plugged or removed (retubing). From the inspection data (the result of statistics), defects like corrosion, pitting, wall loss, wear, etc., that resulted in notable material loss were identified. Inspection data also summarized where the defects were located (like between the first baffle and the second baffle) and are helpful for further research. After analysis using ECT reports, the defective tubes were categorized according to their defect percentage and location, which helps to do retubing effectively by avoiding the 100% retubing concept.