Calibration method of ultrasonic flaw detection and quality control method and production method of tubular body

Abstract

Ultrasonic flaw detection at the welded portion (2) of a tubular body (1) is performed at least in the axial direction of the tubular body, a defect judgment threshold is determined based on the difference of signal strength between the total area of defects existing in the region of an ultrasonic beam on the welded surface and an artificial defect, and then quality control of the tubular body isperformed by the defect judgment threshold. From the defect density on the welded surface at the welded portion in the axial direction of tubular body determined from a desired quality level and the area of the ultrasonic beam on the welded surface, an equivalent defect diameter is determined based on the total area of defects existing in the region of the ultrasonic beam and then the defect judgment threshold is determined based on the difference of signal strength between the equivalent defect diameter and the artificial defect.

Description

[0001] technology area [0002] The present invention relates to an ultrasonic flaw detection correction method for detecting microscopic defects occurring in welded portions of welded steel pipes with high precision, a pipe body quality control method, and a manufacturing method. Background technique [0003] The quality of welded parts is very important in welded steel pipes, and in-line flaw detection of welded parts is generally performed by ultrasonic oblique flaw detection in the manufacturing process. This method is as follows: Ultrasonic waves are incident obliquely on the testing surface of the testing material, and the inner and outer surface defects and internal defects of the testing material are detected from the reflected waves reflected by the defects. Usually, for example, in electric resistance welded steel pipes, the reflection method is applied to an ultrasonic beam with a 5 MHz and a refraction angle of 45° to detect mm-sized defects, such as defects such a...

AI Technical Summary

Problems solved by technology

First of all, in the method of Patent Document 1, the problem is that since the focused ultrasonic beam has a narrow width, it is necessary to perform flaw detection in the entire area in the depth direction of the welded part (the direction of the steel pipe wall thickness), requiring a plurality of channels. Not only does the equipment cost increase, but also it is very troublesome to adjust the position when the size of the tube is changed.

Also, when the shape of the defect is not a pore but is located inside the wall thickness in a planar shape like a penetrating defect or a cold joint, the reflected wave travels in a direction different from the incident direction, making detection difficult

[0008] In addition, in the method of Patent Document 2, since one array probe is sufficient, and the setting at the time of size conversion can also be performed electronically, the former problem shown in Patent Document 1 does not exist, but the latter problem still not resolved

[0009] In addition, when the shape of the defect is planar as described above, for example, in electric resistance welded steel pipes, since the weld portion is upset, the width of the defect viewed from directly above the weld is very small and is 100 μm or less. In the methods of Patent Document 3 and Patent Document 4, the reflected waves from defects are actually very weak and difficult to detect in many cases.

In addition, since the 1 to 2 mm near the surface echo becomes a failure zone due to the reaction of the surface echo, there is a problem that it cannot be detected when the position of the defect is located near the outer surface.

[0010] In this way, in the inspection technology for detecting microscopic defects on the order of hundreds of microns or less that occur on the welded part in the pipe axis direction of the welded steel pipe, there are problems such as insufficient detection performance, so it is difficult to respond to the increasingly stringent quality control requirements in recent years. , it is necessary to develop a technique to solve these problems

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