This standard specifies that full-penetration welds of under-ferrite copper with a thickness of 6 mm or more should be tested using an ultrasonic flaw detector (hereinafter referred to as a flaw detector) with a basic display using the pulse reflection method (hereinafter referred to as a flaw detector). This section specifies methods for detecting flaws and measuring their positions and dimensions when performing flaw detection (flaw detection) manually. However, this does not apply to joint welds during the manufacturing process of steel pipes.