AC electromagnetic coil eddy current testing to the metal surface of the member induced eddy current non-destructive flaw detection technology. It is suitable conductive material, including defects in ferromagnetic and non-ferromagnetic metal material component testing.
Due to eddy current testing in the detection coil does not require close contact with the member, and without full coupling agent between the coil and components, easy to implement test automation. However, eddy current testing is only suitable for the conductive material, or only detect surface defects near the surface layer, inconvenient to use in complex shape member.
Principle when alternating current through the coil, if the voltage and frequency used unchanged, the current through the coil will change. If placed in a coil of metal pipes, thick-walled ssaw steel pipe circumferential surface induced current, that vortex. Magnetization direction opposite the direction of the applied magnetic field eddy current, so will offset part of the applied current, so that the impedance of the coil, have both been changed by the size of the current phase. Changes in diameter, thickness, conductivity and permeability of the tube and the presence of defects, will
affect the impedance of the coil. If the holding other factors constant, only the defect caused by the impedance of the signal extraction, amplification by the instrument and to detect, can achieve the purpose of testing. Eddy current signals can provide not only the size of the defect, while some may be due to the eddy current test phase a vortex at the surface behind the surface of the vortex, using a phase analysis can determine defective bit T (depth).
Detection coil eddy current testing, in order to adapt to different testing purposes, in accordance with the relationship between the subject and the detection coil member into through the coil, the coil within the formula and put coils in three categories. For use through the coil when the workpiece is inserted into and through the detection coil. When the pipe is detected, it is sometimes necessary to coil into a thick-walled spiral pipe internal inspection, is used in the formula coil. When using the formula put t (dot) coil, the coil is placed on the surface of the workpiece is detected checked.
This coil is small, generally with an internal coil core, high sensitivity, easy to carry, suitable for surface crack inspection of large components and sheet, strip and so on. In accordance with the use of the detection coil, it can be divided into absolute coil type, coil type standard comparison and self-comparison, three types. Only one detection coil called absolute coil. With two detection coils connected to a differential form, known as the standard comparison coil. Using two coils placed on the same subject in different parts of the member, as a comparative standard coil, said self-comparison, is relatively standard coil special case.
Optimum efficiency control of high frequency welded pipe in welding process
In most cases, optimized welding process, power loss can be reduced 50% and can improve the welding quality, reduce downtime, increase production.
Stress on the trench corrosion of high-frequency straight seam resistance welding pipe
Trench etching is generally believed that acute heat in the welding process, the results of local tissue metal and chemical change caused by quenching.
Technology of straight seam high frequency resistance welded steel pipe
Factors that affect the raw material for the steel pipe welding quality affect the quality of raw materials are mainly steel mechanical properties unstable surface defects and strip geometry deviation big three aspects, therefore, we should focus on these three aspects of control.
