MSRR

NDT Methods for Flaw Detection during Welding

Final ultrasonic TOFD trials held at Nordon (FR) (Oct 1997)
A collaborative research project funded by the EC under the BRITE-EURAM II "Industrial and Materials Technologies" Programme.

Partners:- Mitsui Babcock Energy Ltd. (UK)
Institut de Soudure (FR)
Isotopen Technik Dr. Sauerwein GmBH (GER)
Nordon & CIE (FR)
The University of Surrey (UK)

The final ultrasonic TOFD trials of the BRITE-EURAM II project 'NDT Methods for Flaw Detection During Welding' took place in the first week of October 1997 at Nordon and CIE's workshops in Nancy, France. The trials were attended by staff from Mitsui Babcock, the Institut de Soudure, the University of Surrey and, of course, by all staff involved with the project at Nordon. The aim of the trials was to demonstrate NDT using TOFD whilst welding was taking place - i.e. the ultrasonic probes were to be placed a short distance behind the weld torch. This was to be demonstrated with both SAW and TIG welding. The problems associated with such a scenario include high temperatures (sometimes exceeding 250 degrees C on the surface of the parent plate), incomplete weld geometries, automated probe coupling, electo-magnetic and electrical interference from the welding equipment, and suitable on-line interpretation of the scan results.

Figure(1) - A scene from the trials: demonstration of TOFD inspection during TIG welding.
The ultrasonic probes can be seen located behind the weld head.

The trials successfully demonstrated the techniques and methods developed during the four year study to undertake NDT during welding. A number of welded test plates were prepared - one set of TIG welded 25mm thick steel, the other submerged arc welded 80 mm thick steel. Defects were deliberately implanted into the testpieces by Nordon welders at various stages of weld completion - Figure 2 shows an example of this work in progress. These defects included tungsten inclusions (for TIG welds), root cracks, porosities, lack of fusion, slag inclusions (for SA welds) and lack of penetration. The techniques that are required in order to implant suitably representative defects into the welds were developed by Nordon at an early stage in the project.

Figure(2) - a Nordon welder deliberately inserts a defect in one of the SAW test plates.

Prior to the trials, Mitsui Babcock had undertaken extensive investigations into the problems of performing TOFD inspections on incomplete weld geometries, at high temperatures and in close proximity to live welding apparatus. A probe housing was designed which incorporated both water cooling and a mechanism for automatic couplant application and removal. A manipulator rig capable of being mounted on a range of automated welding machines was designed and was interfaced to an AEA Microplus data acqusisition system. The probe manipulator is shown below in Figure (3).

Figure(3) - A side view of the probe manipulator attached to a TIG welding machine.
The probes are housed in perspex shoes either side of the weld. Water cooling is applied to the
probes via the clear plastic tuning. Couplant is pumped to the shoe via the blue tubing and
is then removed via the red tubing. The wheel encoder to track the probes can be seen in the background.

At the trials, once the ultrasonic probe rig was commissioned, TOFD scans were made at increasing stages of weld completion whilst the plates were being automatically or semi-automatically machine welded. These scans were interpreted as they were acquired by staff from Mitsui Babcock and the Institut de Soudure. In addition, the Microplus system was networked with a Windows NT PC running image processing software which has been developed at the University of Surrey. TOFD scans could be processed by the UoS software immediately upon completion of the scan run.

Figure(4) - An example TOFD scan acquired during trials after undergoing processing with the UoS software.
The scan is of a metre length of TIG weld at approximately 75% completion. The weld contains several defects which have
automatically been recognised by the software (labelled in red).

The role of the image processing software is to automatically flag the presence and location of any defects within the weld in order that on-line fully automatic inspection is possible. The software may also be used to cue a manual inspector to any welding problems as they manifest themselves in the on-line NDT data. The welded testpieces are currently undergoing sectioned (destructive testing) by the Institut de Soudure which will enable a full objective assessment of the performance of both the TOFD scanning procedure and also the automatic software.

Aknowledgements

This work is funded by the European Commission under the BRITE-EURAM II programme (project no. 5907).
The BRITE-EURAM project NDT Methods for Flaw Detection During Welding

Further information :-

For further information on this work please contact either the project coordinator:-

Dr. Barrie Shepherd,
Mitsui Babcock Energy Ltd.,
Technology Centre,
High Street, Renfrew,
PA4 8UW. Scotland.
tel: 44 (0)141 8862201
fax: 44 (0)141 8853370

or, for the University of Surrey :-

Shaun Lawson

Author: Shaun Lawson (s.lawson@surrey.ac.uk), October 1997.

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