The Research And Implementation Of Water Jet Coupling Inspection Method In Ultrasonic Automatic Testing System Of Helical Weld

The inner quality of weld is the key factor of the safe operation for the helical seam submerged-arc welded pipe (HSAW), and as one of the main methods of inspecting the weld, the reliability of the ultrasonic automatic testing is particularly important. In this paper, the author analyzes the problems which exist in the traditional ultrasonic automatic testing. The probe coupling effect is the main factor influencing the inspection results. For this situation, this paper proposes a new way of coupling, designs and manufactures a water jet coupling device. The water jet coupling device changes the coupling method of probe to improve the probe coupling effect, and fundamentally to solve the risk of the traditional ultrasonic automatic testing coupling methods.First of all, this paper demonstrates the feasibility of water immersion method ultrasonic testing in steel pipe weld in theory, compares the longitudinal wave inspecting and the shear wave inspecting of water immersion method, and ultimately determines to use the water immersion method with shear wave detection for off-line test.Before the off-line test, testing instrument of ultrasonic testing system including probes and coupling agent is chosen reasonability, and the test object is selected including all types of ultrasonic testing block such as the standard test block, the reference blocks and the analog block, and each off-line test sequence of tests and indicators is also determined. Through the analysis, the off-line test results of the water immersion method meet the standards and testing requirements, therefore, the water immersion method can replace the traditional direct contact method.According to the off-line test results, this paper designs a water jet coupling device by using the acoustic characteristics of the ultrasonic wave refraction in different interfaces. The function of the device is verified after the completion of the validation, and the instability of water flow is improved, the device can meet the inspecting requirements.Finally, the on-line test of the water jet device is carried out. In the test process, a comparison pipe is made according to the requirements of relevant standards, and the paper carry out comparison test, dynamic and repetitive authentication at all the artificial references. Test results show that the coupling effect of water jet coupling device meet the requirements of automatic ultrasonic testing, especially in the vertical hole detection ability is superior to the traditional direct contact method.The water jet coupling device also has other advantages except to solve the coupling instability problem of the direct contact coupling method, for example:it is more convenient for sensitivity adjustment, easier to get a higher sensitivity and it has better dynamic waveform; For different pipe diameter and wall thickness of steel tube, the water jet coupling method only needs to adjust the angle of the probe to meet the needs of the testing, but the traditional direct contact method needs purchasing many probes according to different steel pipe specification; the water jet coupling method reduce the use-cost because that there is no direct contact and friction between the probe and the surface of pipes.