Eddy current testing is an NDT inspection method used to detect defects in heat exchanger tubing. Conventional eddy current testing as per ASME Scetion V is used for inspection of non-ferromagnetic tubing such as stainless steel, titanium, copper, brass, copper-nickel alloys, hastelloy, etc. The technique selection for ECT depends on the tube material and is discussed in Paper 54.

NDE Associates, Inc. conducts ECT inspection using four frequencies in both differential and absolute modes. The differential mode detects pits and cracks and the absolute mode detects gradual wall loss. We use multi-frequency testing for the following two reasons:

1. To differentiate between defects and metallic deposits. This is essential because metallic deposits will produce eddy current signals that resemble defect signals. Improper resolution of signals will result in unnecessary plugging of tubes.
2. To detect defects under the support plates. This is done by using a two frequency mix to cancel the support plate signal and detect defects under the support plate.

ECT signals from metallic deposits can be misidentified as defect signals. Discrimination of such signals is essential for a reliable inspection. The photo above shows copper deposits on a Inconel tube.

NDE Associates, Inc. uses the state of the art eddy current testing machines RDTech TC 5700 and MS 5800. The machine is capable of conducting a multi-frequency test and allowing a pull speed of 6 feet/sec.
 

ECT OF AIR CONDITIONING CHILLER TUBING

ECT has a major application in the Heating, Venting and Air-conditioning (HVAC) industry. Air conditioning chillers include an evaporator and a condenser. The tubes in these components must be periodically inspected to avoid leaks during operation. Evaporator and condenser tubes are inspected for damage that includes ID and OD pitting, wear, cracking in fins, etc. Evaporator tubes are also inspected for freeze bulges.
 

OTHER APPLICATIONS

In addition to the inspection of heat exchanger tubing, ECT has several other applications. They are:

• surface crack detection, e.g. pipes, vessels, turbine blades
• clad overlay measurement, e.g. stainless steel/inconel clad over carbon steel
• paint thickness measurement
• wear measurement, e.g. gas turbine blades

For details of other applications click here.
 

ECT CERTIFICATIONS

Several companies in the US have initiated an effort to assure that technicians are proficient in eddy current testing. These companies require technicians test mockup heat exchangers that have a variety of defects that represent actual defects encountered in eddy current testing.
NDE Associates, Inc. technicians have successfully qualified for the following companies.

• Shell Oil Company - Certified for ECT
• Chevron Oil - Certified for RFECT
• Lyondell Arco - Certified in ECT and RFECT
• EPRI - Certified in ECT

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NDE Associates, Inc.
515 Tristar Drive
Webster, TX 77598
Phone: 281-488-8944    Fax: 281-488-8485