在GB/T 29712-2013《焊缝无损检测超声检测验收等级》标准中，焊缝超声波检测显示验收有2种评定技术，基于显示长度和回波幅度的评定技术。显示长度的测量采用固定回波幅度等级技术，AL2（验收等级2）测量回波超过H₀-14 dB的探头移动距离，AL3（验收等级3）测量回波超过H₀-10 dB的探头移动距离，所测得的距离即为缺欠显示长度。依据显示长度与板厚的倍数关系和不同的板厚区间确定AL2或AL3的验收等级，记录等级为相应验收等级-4 dB。由验收等级和记录等级，将缺欠显示回波幅度划分为三个区域，即合格区、待定区和判废区，很好地解决了基于缺欠显示回波波幅评价的难题。结合具体的检测实例，论述了实际检测中缺欠显示长度和回波幅度评定技术在缺欠显示验收中的应用。

In the GB/T 29712-2013 standard, the assessment of indications for ultrasonic testing of welds has two evaluation techniques for acceptance purposes, and present paper mainly discusses the evaluation based primarily on length and echo amplitude of the signal indication. The measurement of the signal indication length adopts fixed echo amplitude level technique, the AL2 (acceptance grade 2) measures probe movement distance of echo amplitude that exceeds H₀-14 dB, and the AL3 (acceptance grade 3) measures probe movement distance of echo amplitude that exceeds H₀-10 dB. The measured distance is the imperfection length of the signal indication. The AL2 or AL3 acceptance levels are determined according to the multiple relationships between the signal indication length, the board thickness and different thickness ranges, and the record levels are equal to the acceptance levels minus 4 dB. By the acceptance levels and record levels, the imperfection echo amplitude of the signal indication is divided into three regions, and they are the qualified zone, the undetermined zone and the disqualified zone. It is believed that this division is a good solution to the problem of defect echo amplitude evaluation based on display. Based on the test of specific example, a detailed discussion was given in present paper to show how to assess the imperfection signal indication in the practical test based on the imperfection length and echo amplitude of the signal indication.