由于聚乙烯材料的声学特性、热熔接头的结构形状干扰以及未熔合缺陷对超声波响应不灵敏等因素，使热熔接头的超声波检测有效性未得到承认。在大量试验的基础上，提出一种针对聚乙烯管道热熔接头超声检测的方法—耦合聚焦技术。该方法是通过配制一种声速和声阻抗与聚乙烯相匹配的耦合剂，使球形曲晶片聚焦的声束通过耦合剂时产生会聚，在扫查时聚焦区能始终贯穿接头熔合区。通过大量带有典型缺陷试样的对比试验，验证该方法能可靠地检出热熔接头中1 mm的体积型缺陷、1 mm高的面积型缺陷，满足工程检测的需要。

The butt fusion process is a widely used method for connecting PE (Polyethylene) pipes. Conventional ultrasonic test is unable to detect defects due to heavy ultrasonic attenuation, disturbance by the structure of the joint, and the weak acoustic response caused by lack of fusion. A technique named coupling focusing ultrasonic technique used for testing PE butt fusion joints was developed in this paper based on large number of experiments. The characteristic of the technique is to get a special couplant with almost the same sound velocity and acoustic impedance of Polyethylene. Through the couplant, sound beams are converged by spherical lens, entering the PE material with focusing zone overlapping the fusion area of the joint. Based on the results of detection experiments of test samples accompanied with typical defects, it is proved that the technique has a good testing ability for volumetric defects with 1mm in diameter and planar defects with 1mm in height, which can meet the testing requirement for welding joints in engineering.