NDTnet 1998 Aug, Vol.3 No.8

Abstract

Since the late 1950's (Schmidt, 1989), remote field eddy current technology has been applied to the inspection of large diameter steel tubing, primarily in the oil and gas industries. The technology allows detection of both internal and external flaws in the tube walls, using a driver/sensor system which passes through the inside of the tube to be inspected. The most significant difference from conventional eddy current inspections used on non-ferrous tubes is the large spacing between the excitation coil system and the receiver system. This avoids direct coupling between the driver and pick-up systems and relies on indirect coupling via magnetic field in the tube wall, Although originally applied on large tubes, e.g. Oil-well casings, it has more recently been used on smaller tube found in power generating systems and petrochemical plants.

Development of instrumentation and transducer technology has continued over this period and recently accelerated as applications in smaller tubing have become increasingly important. In parallel with work on steel tubing similar developments have been taking place in the inspection of non-ferrous tubing, although instrumentation is often quite different.

Hocking NDT has been working on the transducer and instrumentation problems posed by the non-ideal condition of the test pieces and the noise caused by this, thermal effects and other factors. The noise problem is aggravated by the requirement for unusually high levels of amplification due to the small signals which have to be detected and measured. These technical challenges limit both minimum flaw size detectable and inspection speed, and solutions have generally required AC operated instrumentation with considerable postprocessing of the signals obtained.

This paper will review the work done at Hocking NDT to overcome these limitations and the results achieved on calibration specimens and an in-service heat exchanger using a portable battery-operated instrument able to inspect both ferromagnetic and non-ferromagnetic tubing.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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