Ghia, Olivero, Piovano
# 2004 Milan
Nowadays the major determinants for the evaluation of polyethylene (PE) pipe welding are still visual examination of weld bead quality (for butt fusion) and destructive tests. Nevertheless during the last decade a great effort has been done in studying and attempting the development of suitable Non Destructive Evaluation (NDE) methods to reliably assess the integrity of PE joints and ensure a long term operation life for thermoplastic welds. Goal of this contribution is to present the research activity carried out by Italgas in this field. Both XRays and ultrasonic techniques have been tested always finding out good results as far as standard flaws (such as inclusions and voids) are concerned and difficulties in the cold weld detection. In particular, as for ultrasonic analysis, both Pulse Echo and Pitch Catch techniques have been taken into consideration. Ultrasonic tests were accomplished on samples purposely prepared with different kinds of flaws, so as to reproduce all possible defects or weaknesses affecting field welds (gas and bulk inclusions, cold welds,…). Afterwards all the specimens have been subjected to Destructive Evaluation (DE) tests, executed in accordance with the international standard ISO 13953. Comparison between DE and NDE led to the aforementioned results. At present other promising techniques, such as time of flight diffraction and ultrasonic array approach, are under evaluation and preliminary results will be presented.