方管表面缺陷的检测方法，主要有以下五种：一电涡流检测.电涡流检测有多种形式，常用的有常规涡流检测、远场涡流检测、多频涡流检测和脉冲涡流检测等，利用电涡流传感器对金属进行感应，方管表面不同缺陷类型和形状将产生不同类型的信号。其优点是检测精度高、探测灵敏度高，检测速度快，能检测待检测管材的表面及亚表面，且不受待检测方管表面油污等杂质的影响。缺点是易将非缺陷结构判定为缺陷，误检率较高，检测分辨率不容易调整。

There are five main methods to detect the surface defects of square tubes: one is eddy current testing. Eddy current testing has many forms, such as conventional eddy current testing, far-field eddy current testing, multi-frequency eddy current testing and pulse eddy current testing. Using eddy current sensors to induce metal, different types and shapes of defects on square tubes surface will produce different types of signals. It has the advantages of high detection accuracy, high detection sensitivity, fast detection speed, can detect the surface and sub-surface of the pipe to be tested, and is not affected by the impurities such as oil contamination on the surface of the square pipe to be tested. The disadvantage is that it is easy to judge the non-defective structure as a defect, the false detection rate is high, and the detection resolution is not easy to adjust. 二超声波检测

Two-Ultrasound Detection

利用超声波进入物体遇到缺陷时，一部分声波会产生反射，发射和接收器可对反射波进行分析，就能异常精确地测出缺陷来。超声波检测常用于锻件检测，检测探伤灵敏度高，但是不易检查形状复杂的管材，要求被检查的方管表面有一定光洁度，并需有耦合剂充填满探头和被检查表面之间的空隙。

When ultrasound enters an object and encounters a defect, a part of the acoustic wave will produce reflection. The transmitter and receiver can analyze the reflected wave, and the defect can be detected abnormally and accurately. Ultrasound detection is often used for forging detection, which has high detection sensitivity, but it is not easy to inspect the pipe with complex shape. It requires that the surface of the inspected square pipe should have a certain degree of smoothness, and the coupling agent should be used to fill the gap between the probe and the inspected surface.

三磁粉法检测

Detection by three magnetic powder method

磁粉法检测的原理是在方管材料中实现磁场，根据缺陷处的漏磁场与磁粉的相互作用，当表面和近表面有不连续或缺陷时，则在不连续处或缺陷处磁力线发生局部畸变产生磁极。其优点是设备投资少，可靠性高，具有直观性。缺点是操作成本高，不能对缺陷准确分类，检测速度较低。

The principle of magnetic particle method is to realize magnetic field in square tube material. According to the interaction between leakage magnetic field at defect and magnetic particle, when there is discontinuity or defect on surface or near surface, the magnetic line at discontinuity or defect will distort locally to produce magnetic pole. Its advantages are less investment in equipment, high reliability and intuition. The disadvantage is that the operation cost is high, the defect can not be accurately classified, and the detection speed is low.

四红外线检测

Four Infrared Detection

通过高频感应线圈，在方管表面产生感应电流，感应电流会导致缺陷区域消耗更多电能，引起局部温度升高，通过红外线检测局部温度，从而确定缺陷深度。红外线检测一般用于平直表面的缺陷检测，不适合检测表面不平整金属。

Through high frequency induction coil, induction current is generated on the surface of square tube. Induction current will cause more electric energy to be consumed in defect area, causing local temperature to rise. The defect depth can be determined by infrared detection of local temperature. Infrared detection is generally used for flattening surface defect detection, not suitable for detecting surface irregularity metal.

五漏磁检测

Five magnetic flux leakage detection

方管的漏磁检测方法和磁粉检测方法非常相似，适用范围、灵敏度和可靠性较磁粉检测方法更强。

The magnetic flux leakage testing method of square tube is very similar to that of magnetic powder testing method, and its application scope, sensitivity and reliability are stronger than that of magnetic powder testing method.