Assessment of PVC joints using ultrasound

Abstract

In the context of the present work it is hypothesized that the condition of a PVC push-fit joint can be obtained from the analysis of the joint's gap width. A perfectly jointed and aligned pipe, for example, should have a constant gap for the complete pipe diameter while a bent joint should show variations of the gap width with the diameter. Therefore, laboratory tests were performed to test the applicability of ultrasound in the assessment of PVC push-fit joints which are ubiquitously used in the Netherlands. In those tests the potential of ultrasound to detect changes in geometrical alignment of PVC pipes was evaluated using a specially built metallic loading frame. This frame supported two 2-meters ø315 mm PVC pipes connected with a push-fit joint. This pipe could be kept in horizontal position or be bent up to an angle ofca. 5 degrees in 11 uniform steps. Results show that when two pipes have a perfect alignment (zero degrees angle between the pipes) the tested ultrasound tool describes quite adequately the real situation and gives good information about the joint's real condition. However, when an angle is imposed on a PVC joint the ultrasound results are not consistent with reality. This discrepancy is probably due to both longitudinal and shear ultrasound waves echoing back to the transducer from the PVC wall. The creation of both longitudinal and shear waves occurs when an angle between the ultrasound transducer and the object being studied exists. This factor is known to complicate the resulting ultrasound scans and the interpretation of the results. In conclusion, for this application ultrasound inspection is vulnerable to changes in geometrical alignment of assessed pipes. Even being unanimously considered as a potential technique for the inspection of polymeric pipes, ultrasound tool is not capable of giving results that permit accurate detection of all known failure mechanism of joints.