ERW Tube Testing
ERW or Electric Resistance Welded tube is made in a rolling mill by feeding a continuous sheet of steel through sets of convex rollers and passing a high electric current through the joint where the edges are fused together to form a round tube. This welded joint makes a very reliable tube if the weld is properly made along the length of the tube, without flaws or other discontinuities. To detect such flaws, special Eddy Current equipment has been developed by Andec, some of which is shown in the attached photographs with full descriptions.
Inline Eddy Current Full Body Testing System for ERW Ferrous Tubing
This system consists of an encircling test and saturating coil arrangement installed in a highspeed small diameter Electric Resistance Welded tube production line.
It inspects the full body of the tube, and the continuous weld seam, as it passes through the absolute and differential encircling test coil, while it is magnetically saturated to take away its ferritic properties.
In this non-ferrous state small defects are detected in the weld, and throughout the tube wall around the tube, and shown in real time on the control computer display, in a simulated “stripchart” recording.
Detected defects are marked on the tube, down line, with a special computer-controlled paint marker.
Inline Eddy Current Weld Testing System in Thick Wall ERW Ferrous Tubing
This PLC controlled system inspects the continuous weld seam in heavy wall Electric Resistance Welded tubing.
The system is installed close to and right after the weld area to overcome the effect of possible “weld wander”, but requires cooling there to prevent overheating of the Eddy Current test coil.
This special “segment coil” is curved to the appropriate diameter of the tubing and narrow to inspect only the weld area in the center between the magnetizing pole pieces.
The extremely strong magnetic field, produced by the very large magnetizing coil, and two pole pieces on either side of this test coil, make the weld at that point completely saturated and non ferro-magnetic.
In this non-ferrous state small defects are detected throughout the thick weld.
This combination of the large magnetizing coil and heavy pole pieces can saturate a weld thickness up to about 9mm (0.350”), while an even larger coil and pole pieces, installed in another company mill, can saturate a weld of up to about 12.5mm (0.5”).
Detected defects are marked on the tube, down line, with a special PLC controlled paint marker.
Eddy Current Testing System of the Continuous Weld Seam of Small Diameter ERW Tubing
This system inspects only the weld seam of the tube with the use of a special ‘Segment test’ coil, shaped closely to the diameter of the tube.
This test coil is located between the pole pieces of two heavy steel arms, which convey the magnetic field from the center of the large magnetizing coil, to the tube under test.
This strong magnetic field ‘saturates’ the tube weld to make the small area directly under the test coil completely non-ferrous, like copper or aluminum, so that the Eddy Currents will detect any defect throughout the weld.
Calibration can be performed conveniently by flipping the magnetizing arms and test coil upside down, and to the front, so that a short tube with calibration notches can easily be moved from side to side across the test coil (as shown).
Any flaws are shown and recorded by the controlling PLC and marked on the tube down the line.