Ultrasonic testing is a proven technology in plastic pipe Extrusion. This technology is reliable, this is shown also in respect to aeronautics, nuclear and medicine.
Ultrasonics are applied for plastic pipe dimensions of 0.15 - 75 mm wall thickness and 1.0 - 1200 mm diameter. For this measurement range one individual transducer is not enough , but one per Extrusion line is usually sufficient.
Today ultrasonic systems must provide flexible parameter settings, only with this can fast progress in applications follow, which change along with changing pipe products.
The ultrasonic calibration can be done automatically or manually. By automatic methods the accuracy improves by 0.5% - 1%, the manual method gains 1% - 2% . A set-up parameter saving is essential for the manual calibration. Temperature variation at the circumference can only be corrected manually.
The diameter method by ultrasonic is proven by many installations, for large and small dimensions. The joint measurement of outer/inner diameter and wallthickness gains advantages with regard to price, operations, recording and control.
For fixed transducers or reversible transducers various installation positions are already available. The fixed transducer method is inexpensive and reliable. Close to the die this is the only practicable solution.
Close to die measurement will proceed and display its limits by further practical experiences. The Coextrusions Application just started and the demand for layer measurement will increase. The supplieres have to improve the relaibility of the Ultrasonic method and this will need their development efforts.
Many pipe products will demand 100% flaw testing. The practical application under production conditions is at the moment limited to the floor heating pipe market. The demand for 100% flaw detection technology will continue, for other pipe products too. A next article will report more about this and has the title: New advantages for quality control of Plastic Gas Pipes with an Ultrasonic Flaw Detection Rotation Machine .
Rolf Diederichs 19. Dec 1995, info@ndt.net