A method and system for the ultrasonic non-destructive testing of joints in plastic pipes using A-scans. A hand-held ultrasonic transducer is used to perform an A-scan and a comparison made on a response from the interface region of the joint used to determine a quality of the joint. Levels of result can provide a binary output to give an indication of whether or not a defect is present in the joint. Comparison techniques are described. Tests for coupling efficiency and performance are described making the system useable by an unskilled technician. The system finds application in fault detection on electro-fusion welds in plastic pipe joints.