Eddy current flaw detection for seamless steel pipes

Non-destructive testing of seamless steel pipes is an inspection technology that detects internal or external defects without damaging the steel pipe. In recent years, it has been widely used by major seamless steel pipe manufacturers. The non-destructive testing technologies used in the production of seamless steel pipes mainly include ultrasonic flaw detection, magnetic flaw detection, eddy current flaw detection and penetrant flaw detection. Various flaw detection methods have their own scope of use. This article will describe the eddy current flaw detection method for seamless steel pipes.

1. What is eddy current flaw testing of seamless pipes?

(1) Seamless pipe means

With the rapid development of the construction industry, the demand for seamless steel pipes is increasing. Seamless pipes are steel pipes without welds. Compared with welded pipes, seamless pipes have higher precision and stronger corrosion resistance, but the cost It is also higher. Common materials include black carbon seamless steel pipe and stainless steel seamless pipe.

(2) Eddy current flaw detection

Eddy current flaw detection is a non-destructive flaw detection method. Eddy current flaw detection is a flaw detection method that uses the principle of electromagnetic induction to detect surface defects of components and seamless pipes. The detection method is to detect coils and their classification and detect the structure of the coils.

The principle is to use an excitation coil to generate eddy currents in conductive components, and use a detection coil to measure the change in eddy currents to obtain information about component defects.

According to the characteristics of industrial non-destructive testing, in order to achieve automated control of the testing system, steel pipe companies mostly use the traditional core-through coil testing method for eddy current testing of seamless steel pipes below 180mm. For seamless steel pipes above 180mm, if the traditional eddy current method is used for inspection, many problems will occur, which is not allowed by national standards. Penetrating coils detect the circumferential surface of the steel pipe surface. In eddy current flaw detection using penetrating coils, the larger the diameter of the steel pipe to be detected, the larger the circumferential area detected by the coil, and the lower the signal-to-noise ratio. Because of this, the steel pipe eddy current flaw detection standards stipulate that the outer diameter of the through-type coil for eddy current flaw detection shall not be larger than 180mm. In addition, in the through-type flaw detection of large-diameter steel pipes, there are also certain difficulties in the magnetization and demagnetization of the steel pipes. Therefore, whether at home or abroad, point probe eddy current flaw detection equipment is commonly used for flaw detection of large-diameter steel pipes.

2. Eddy current flaw detection method for multi-diameter seamless steel pipes

The detection sensitivity of point eddy current flaw detection is very high, and it has a high detection rate for cracks and wrinkle defects distributed along the axis of the steel pipe; in addition, point eddy current detection can also suppress the ambient temperature and workpiece transmission vibration. Impact of impact. More importantly, the form of the point eddy current probe can adapt to the flaw detection requirements of steel pipes of different diameters.

(1) First, according to the actual situation of the production line, determine the flaw detection method in which the seamless steel pipe spirally rotates along the production line and the probe is fixed. While rotating the steel pipe forward, bring the point probe close to the surface of the steel pipe to complete scanning of the entire outer surface.

(2) Determine the structure of the flaw detection system. First, put the six-channel eddy current probe into the probe trolley, adjust the probe trolley to meet the requirements of the diameter of the steel pipe to be tested by adjusting the screws, and then use the cylinder push-in fine-tuning method to keep the probe trolley detection probe tightly pressed at all times. on the workpiece. To detect the surface of the workpiece, install a pair of universal wheels at both ends of the probe station to keep it at a certain distance from the workpiece to be inspected.

(3) Determine the number of probes. The point probe flaw detection method requires the use of multiple detection probes to increase the scanning distance and improve the detection speed. Eddy current point probes are generally small in size and have high detection sensitivity, but at the expense of detection speed. Increasing the coverage of the probe detection area can increase the detection speed, but the detection sensitivity will decrease.

Article source: https://article-realm.com/article/Business/62406-Eddy-current-flaw-detection-for-seamless-steel-pipes.html