Externally Referenced Remote Field Testing of Finned Ferromagnetic Tubes

Externally Referenced Remote Field Testing (XRFT) is the purely magnetic technique like RFT useful to detect flaws in materials with permeability sufficient to prevent significant penetration of eddy currents. XRFT is primarily used to inspect finned ferromagnetic tubing since special ultrasonic method with rotational probes (IRIS). Using IRIS method for fin fan tubes cooler however clealines became a major limitation to ultrasonic methods. Also speed of UT testing is not satisfactory due to possible missing some small defects. Conventional Remote Field Testing (RFT) is not reliable due to mostly aluminium fins disturbing the electromagnetic field. As a result the Externally Referenced Electromagnetic Technique (XRFT) was developed and used with big success from few years.

XRFT is an electromagnetic technique using the Remote Field phenomena connected with an external reference to eliminate extraneous noises by utilizing a balanced system caused by aluminum (or other metals) fins. XRFT has accuracy rate less than 10% of nominal tubes wall, good sensitivity for gradual wall loses and very high sensitivity for pitting and cracs. XRFT has very good repetability and tubes can be inspected with speed at 25 mm per second with very little cleaning required. This technique has good false positive recognition and has made data analysis easy to interpret. The external reference self comparison differential arrangement uses two differential probes and is setup to provide differential and absolute responses.It essentially combines the self comparison differential coil arrangement with the external reference absolute coil arrangement. The second probe, located in an external reference sample, compares one of its coils with one of the coils in the inspection probe to provide absolute information and detection of long flaws and dimensional variations.

These can be very quickly scanned for both internal and external wall loss defects such as a corrosion, erosion, pitting, cracks, and wear scar.

XRFT can be used to inspect any conducting tubular product with nonferromagnetic fins or coated by non ferromagnetic materials like aluminium, cooper, stainless steel, titanium. Evaluating the quality of products by Externally Referenced Remote Field Testing method is the most effective for ferromagnetic materials like low carbon steels, chrome molly, duplex in units like:

• fin fan cooler
• feedwater heater with finned tubes
• furnace tubes coated by nonferromagnetic materials
• went coolers using bimetallic finned tubes with carbon steel core
• Went coolers with fin fan tubes

Mostly manually pushing probes allows for the checking of about 200 tubes per shift. Institute Gamma utilizes the highest technology of multi-frequency testing equipment including the Zetec's MIZ-27SI and RFT Modified Amplifier with possibility to connect reference probe with standard.

Institute Gamma's qualified engineers and technicians perform maintenance and inspection services.

Benefits of XRFT tube testing are:

• Prevention of dangerous leaks
• Prevention of break down outages
• Accurate assessment of wall thickness loss up to 10% of wall thickness
• Recorded measurement data , forecasting of wall loses, predictive maintenance
• Quantitative method
• Detecting abnormalities of used materials
• XRFT doesn't need water and clean surface like the IRIS method
• XRFT is more sensitive and sizes defects more accurately and quicker than ultrasonic methods