Copper pipe eddy current flaw detection

Oxygen-free copper tube, refined copper and copper alloy pipe, copper content in material represents a significant share of the pipe, collectively known as the copper tube, they have excellent electric conductivity and thermal conductivity performance. Power plant components, chemical equipment, therefore, in the heat exchanger pipe, and the cooling pipe in the air-conditioning unit, often using this type of brass。

(1) Flaw detection method and device

Copper and copper alloy tube eddy current testing method, classified by using form of probe, is through the coil method, rotating point probe method, interpolation method, three kinds of coil。

Due to high production rate of copper and copper alloy tube (more than 100 m/min), so particularly suitable for through the method of eddy current inspection. Besides to do finished product phase detection, because of the size of the tube in the process of production change, the influence of the material temperature change on the inspection are small, so it is easy to for inspection in the intermediate stage. Intermediate stage of testing is often done after the heat treatment scale before cut off. Copper and copper alloy through the type testing generally use the coil, the coil of along the line direction of the distribution of strip shape defect detection sensitivity is low.

Through the type of flaw detection device including: eddy current probe, eddy current flaw detector, marking device, alarm, good or bad points institution. If it is to leave the production line inspection, should also include the establishment of transfer units and up-down material, etc.

（2）contract sample

Copper and copper alloy tube eddy current flaw detection using standard be artificial defects usually adopt the standard stipulated in the country. Through the type testing using artificial defects are mostly hole or half hole。

For general through the type eddy current flaw detection, need to determine the test parameters have detection speed, the fill factor, inspection frequency, amplifier gain and phase detection, filtering band, alarm, power equality. For copper and copper alloy tube eddy current flaw detection, because of their material properties and high detection rate, so in the above conditions, the detection frequency and the selection of filling coefficient is particularly important。

① choices of flaw detection frequency

Detection frequency and defect detection sensitivity relationship is bigger, when selecting a frequency detection, in addition to consider the location of defects detection required (inside or outside the wall), the shape and size, but considering the length of the test coil, detection speed and other factors。

Experience tells us that for flaw detection of copper and copper alloy tube, when using through the coil, general inspection frequency selection in 1 ~ 100 KHZ range。

When using through the type method for detection, with different diameter and wall thickness of copper and copper alloy tube, inspection frequency selection is also different. In general, the larger the diameter, wall thickness is thicker, use frequency is lower, the higher conversely. Table 1 recommended several different copper pipe diameter and wall thickness inspection frequency。

（3）affecting factors

There are many factors can affect eddy current flaw detection,Material changes, artifacts, and detecting coil size, shape and the location of defects, testing conditions It can affect the correct evaluation of the result of the inspection. In copper and copper alloy tube eddy current flaw detection, mainly based on through the coil 。

①　Flaw

②　Material

③　Dimension and filling coefficient of tube\

④　Wall thickness

⑤　Relative position between tube and detecting coil

⑥　Speed fluctuation