EDDY CURRENT TUBE INSPECTION

Eddy current testing uses electromagnetic induction to identify defects in tubing. A probe is inserted into the tube and pushed through the entire length of the tube. Eddy currents are generated by the electromagnetic coils in the probe and monitored simultaneously by measuring probe electrical impedance.

Advantages of Eddy Current Testing

Eddy current test can nearly be applied to all metallic materials
High inspection speeds possible ( ~ 5 m/s)
Eddy current test can readily detect very shallow and tight surface fatigue cracks and stress corrosion cracks (~ 5 microns width and 50 microns depth)
High temperature and on-line testing is possible, even in shop floors
Non-contact / remote / inaccessible testing is possible (couplant is not required unlike in ultrasonic)
Recording and analysis of inspection data is possible (computer based instruments / systems available with data acquisition, storage, analysis and database management)

Limitations of Eddy Current Testing

Like any other NDT technique ECT too has certain limitations, which are overcome to a large extent by the recent advances in the technique. A few key limitations are:

Only electrically conductive (metallic) materials can be tested maximum inspectable thickness is ~ 6mm (12mm possible by tuning frequency, probes, instrumentation etc.)
Inspection of ferromagnetic materials is difficult using conventional eddy current tests.
Saturation ECT and Remote Field ECT are possible for tubes
Use of calibration standards necessary
Operator skill is necessary for meaningful testing and evaluation

Remote Field Eddy Current Testing (RFET)

Remote Field Testing (RFT) is an Electromagnetic Method of nondestructive testing whose main application is finding defects in steel pipes and tubes. RFT may also refer to as RFEC (Remote Field Eddy Current) or RFET (Remote Field Electromagnetic Technique).
This technique suitable for the inspection of ferromagnetic pipes and tubes such as boilers, heat exchangers, and buried pipes.
It allows the detection of pitting (OD/6), general corrosion, wear and cracking at the tube sheet and this with same sensitivity for internal and external flaws.
It is also used for the inspection of thick-wall tubes (up to 12mm).
The typical pulling speed is between 0.1 m/s and 0.3 m/s.
RFT is a lot less sensitive to probe lift-off, wobbling and off-center probe position than ECT.

Internal Rotating Inspection System (IRIS)

IRIS (Internal Rotary Inspection System) is an ultrasonic test method that utilizes water as a couplant in order to inspect tubes from the inside. Full scans are performed as data is acquired through a 360° radius along the tubes' lengths. Upon completion of data collection a highly qualified field engineer with extensive process knowledge of boilers interprets the data on-site, allowing the customer to immediately address areas of concern. IRIS is an ultrasonic system that scans and measures the remnant wall thickness along the full length and circumference of tubes. IRIS uses an immersion pulse-echo technique. The probe is centred in the tube to be inspected and ultrasonic pulses are transmitted along a path parallel to the tube axis. These pulses are then redirected radially to the tube wall by a 45° mirror. The mirror rotates at high speed and scans the ultrasonic beam around the tube circumference. Successive pulses build a screen image of the tube cross section at any given point. By withdrawing the inspection head from the tube at a pre-determined rate the ultrasonic beam is made to describe a helical path, the individual revolutions producing a continuous series of measurements covering the full surface area of the tube.

Capabilities

Inspection of ferrous and non-ferrous tubes, ranging in size from 12.5mm to 75mm internal diameter.
The system provides accurate wall thickness measurements.
Provides 100% coverage of tube circumference.
Sensitive to both internal and external defects.
Typically, 10-12 tubes can be inspected per hour, dependent on tube length.
Defect position can be located in relation to tube length.
Data storage of test parameters and screen image.

MAGNETIC FLUX LEAKAGE FOR TUBE INSPECTION (MFL)

Magnetic Flux Leakage (MFL) is a fast inspection technique, suitable for measuring wall loss and detecting sharp defects such as pitting, grooving, and circumferential cracks. MFL is effective for aluminum-finned carbon steel tubes because the magnetic field is almost completely unaffected by the presence of such fins and this technology is good for:

Feed Water Heaters
Air Coolers
Carbon Steel Heat Exchangers

hidden

GPTI – GROUP OF COMPANIES

+971 6 568 2435

+971 52 608 5790

Tube Inspection (ECT / IRIS / MFL / RFET)