TWI Industrial Member Report Summary 465/1993
By G A Georgiou and I A Macdonald
This report summaries part of TWI's core research programme on NDT of welds in plastics and composites. This study has concentrated on thermoplastics, in particular polyethylene. The major objectives were to develop ultrasonic and radiographic testing procedures for polyethylene pipes joined by hot plate butt fusion. The procedures were developed on pipes with diameters greater than 180mm and thicknesses greater than 12mm. The underlying techniques, however, can be used on testpieces other than pipes, and on a range of different polyethylene types and thicknesses.
The absorption characteristics of polyethylene to radiation and ultrasonic energy can vary significantly from one polyethylene type to anolher. However, some types can be grouped together for the purpose of exposure charts, image quality indicators (IQls) and ultrasonic calibration blocks.
A range of lQls has been manufactured from polyethylene and compared. There include ASME plaques, British Standard step wedges and wire types. Prototype radiographic procedures were found to be more reliable in detecting and sizing flaws of interest (ie inclusions, voids and cold welds) than the prototype ultrasonic procedures.