Ultrasonic inspection of welded tubes
A: tube to be tested
B: immersion test chamber with ring of ultrasonic sensors
C: operator panel for entering and visualisation of the ultrasonic parameters
D: signal lamp (tube defect, system warning)
E: ultrasonic pre-amplifier F: filter unit for coupling water treatment
There are many applications for welded tubes with small diameters und thin walls. Such tubes are being efficiently used for example in heat exchangers (chemical industry, desalination plants etc.). The inspection of these tubes is a major NDT challenge because even small tolerances during the forming stage will cause a large deviation of the welding seam position in circumferential direction.
The KARL DEUTSCH company has built an ultrasonic testing system for the Fischer Group in Achern (Germany), an internationally leading manufacturer of precision tubes. The small diameters of the tubes (starting from 10 mm), small wall thicknesses (starting from 0.4 mm) and small-sized defects (notch depth starting from 0.1 mm) were challenges for this project. The proven online solution of the HRP-system was a suitable setup for this task. This system is normally being used for the inspection of seamless tubes with a high testing speed of up to 120 m/min. For this project, the high testing sensitivity for small wall thicknesses over the entire circumference of the tube was of higher importance. Due to the full coverage of the entire tube volume, a seam tracking was not necessary. Thus the use of a compact and low-maintenance mechanics became possible.
The tube is being completely inspected for longitudinal defects (defects in the tube axis direction) by a ring of ultrasonic sensors, while being fed through the immersion test chamber. The normally required closing mechanism is not necessary in this case. When testing individual tubes, this mechanism avoids coupling liquid within the tube and also prevents the test chamber from running dry. Since this is not required in this case, a compact design was implemented which is robust and requires little maintenance compared to systems with rotating probes. The specially designed probes are connected by short cables. This way, capacitive or inductive transmitters between probes and stators are not needed, thus leading to a testing concept which provides a high signal-to-noise ratio.
The pool-independent KARL DEUTSCH company is, since its foundation in 1949, involved in development and fabrication of NDT instruments. Digital and analog ultrasonic flaw detectors, wall thickness gauges, coating thickness gauges, crack depth gauges, ultrasonic testing systems, instruments and accessories for magnetic particle testing, and penetrants are contained in our products range. Characterised by continuous innovation and reliability of the products, the trade marks ECHOGRAPH, ECHOMETER, DEUTROFLUX, LEPTOSKOP, FLUXA, KD-Check and RMG are well known world-wide. Application experience, theoretical knowledge and manufacturing know-how of more than 6 decades as well as the standard compliant quality management guarantee state-of-the-art instruments and accessories and a top position concerning quality, reliability and economy also for the future.