Research On X-radiographic Test And Ultrasonic Test Of The Fusion-butt Welds Of Polyethylene Gas Pipe

The NDT of the fusion-butt weld for the gas-pipe has been lack of an accepted standardor regulation. According to the character of polyethylene (PE) acoustics and material, we usethe experiences of the common X-radiographic test (RT) and ultrasonic test (UT) for thesteel material for reference, after testing and comparing, we know that the internal defect inthe fusion-butt weld can be tested by the RT or UT, the result of RT or UT can be proved byeach other.The common X-ray detection apparatus can be used for the RT of the PE fusion-buttweld. We use step-wedge made of PE to be exposed by different parameters, then a series ofradiographs can be got, so the exposure charts can be drawn, we test and verify that theexposure charts are right and the definition and image contrast of the radiographs for a block(with side drilled holeΦ1) can be accepted. Lower exposure energy is better for RT to thePE fusion-butt weld. The exposure chart is just suit for the testing apparatus, not suit forother apparatuses even they’re the same type. The bulky defect such as porosity andinclusion can be detected easily, but the area defect such as incomplete-fusion will be hard todetect.The ultrasonic test (UT) type is pulse reflection. We use the common digital ultrasonictest instrument. The special test block we use is made of PE, it is suit for the angle probewhich its’ wedge is made of PE. We survey the sound speed of PE, probe delay, beam indexpoint and K value. Through the test using the special block and probe, we draw thedistance-amplitude curve, so we can detect the PE fusion-butt weld. Using the block with twoarc-faces is better for surveying the sound speed of PE, probe delay and beam index point.The edge made of PE is used in the single transducer probe can obtain pure longitudinal wave.We find that the frequency of the crystal in the probe should be low, generally we use1.25MHz, and its’ size can be13mm×13mm, bigger size is not better.We make some test joints with circled and sliced inclusion, porosity and incompletefusion preset, RT and UT is used separately, the inclusion and porosity can be detectedseparately, but the incomplete fusion is hard to be detected especially in RT. It shows that RTand UT can be used in the fusion-butt weld for the polyethylene pipe for gas, common defectcan be detected easily. The incomplete fusion needs some more tests to find a better way.