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Project Outline

Technical Update

Development of inspection techniques
The two different joint types require different inspection techniques. The inspection technique for EF joints used a normal (0°) linear scan, focused at the fusion zone between the fitting and the pipe (Figure 1a). Since the heating wires are located above the fusion zone, sufficient resolution to be able to see both the wires and between the wires is required. Inspecting BF joints required the use of angled ultrasound beams and a combination of four different techniques was used in order to obtain full coverage of the weld area: self-tandem, sector pulse-echo, creeping wave and time-of-flight diffraction (TOFD) (Figure 1b). The techniques are, in most cases, complimentary.

Figure 1: Inspection techniques for a) EF joints, and b) BF joints.
Figure 1: Inspection techniques for a) EF joints, and b) BF joints.

A novel open-face water wedge was designed and manufactured in order to achieve good acoustic matching with the PE fitting of EF joints (Figure 2a). The water wedge had a sealing skirt fitted, to keep the water in the wedge while it passes over the surface features on the EF fitting. For BF joints, angled open face water wedges were used (Figure 2b). The angle of the wedges was optimized to minimize the electronic steering by the transducer elements.

Figure 2: Water wedge/probe assembly used for a) EF, and b) BF inspections.
Figure 2: Water wedge/probe assembly used for a) EF, and b) BF inspections.

In order to develop the PAUT technique for the EF joints, initial inspection trials were carried out using unwelded EF fittings, based on the assumption that, if sufficient resolution can be achieved to detect the wires, the fusion zone located just below the wires can also be inspected. When developing the inspection techniques for BF joints, unwelded pipe samples with artificial flaws (flat bottom holes (FBHs) machined into the pipe end and slots machined in the middle of the pipe) were used, covering a range of pipe diameters between 180 and 710mm (7 and 28 inches). The FBHs were used to evaluate the tandem and the sector pulse-echo techniques; the slots were used to evaluate the creeping wave and TOFD techniques. In Figures 3 and 4, data from scans using 4MHz transducers on the 225mm (9 inch) diameter pipe containing FBHs and slots, respectively, are shown. The top part of each figure shows a schematic of the pipe with the artificial flaws. The centre image shows the B-scan of the sector pulse-echo scan in Figure 3 and of the creeping wave scan at 78° in Figure 4. In the lower image the B-scan of the tandem scan is shown in Figure 3 and of the TOFD scan is shown in Figure 4.


Figure 3: B-scan images from sector pulse-echo and tandem scans on 225mm (9 inch) diameter PE pipes containing FBHs.


Figure 4: B-scan images from creeping wave and TOFD scans on 225mm (9 inch) diameter PE pipes containing slots.

As can be seen in Figure 3, all of the FBHs can be detected using the sector pulse-echo technique and all but the 1.5mm and the 2mm inner FBH can be detected using the tandem technique. Both creeping wave and TOFD techniques detected all four slots (Figure 4).

Scans were carried out on the different pipe sizes using probes of different frequencies in order to optimize the PAUT techniques and procedures for pipe sizes between 180 and 710mm (7 and 28 inches). The welded samples containing deliberate flaws are currently being inspected using these procedures in order to determine the limits of detection for each type of flaw, pipe size and joint type.

Development of inspection system
A completely new PAUT system is being designed and manufactured, where each component has been optimised specifically for inspecting PE pipes. The system is comprised of the following components:

  • Phased array probes
  • Probe shoes
  • Scanning system with probe holders
  • Flaw detector

A flexible scanning system has been designed and manufactured that will enable full 360° rotation around both BF and EF joints in a wide range of pipe sizes (Figure 5). It comprises a main carriage that is held in position around the pipe by several links and an adjustment mechanism. The carriage contains an encoder and also the support for the probe holders for the BF and EF joints.

Figure 5: Flexible chain link scanner: a) arrangement for inspecting BF joints, b) arrangement for inspecting EF joints.
Figure 5: Flexible chain link scanner: a) arrangement for inspecting BF joints, b) arrangement for inspecting EF joints.

Since the aim of the project is to have the flaw detector mounted on the carriage of the scanner with wireless connection to a remote computer, a new compact phased array flaw detector with the ability to operate in a harsh environment has been designed and manufactured. In addition to the hardware, prototype ultrasonic phased array NDT data acquisition and analysis software is being developed, including extensive design of the ultrasonic beam control electronics and the data processing within the instrument.

The complete PAUT system, including instrument, probes and scanner will be assembled and assessed in the field at the end of the project in order to evaluate the sensitivity, reproducibility and ease-of-use of the system.