X-ray vision at your computer - a training course in weld radiography
TWI Bulletin, November/December 2002
Martin Bourton joined TWI in 1987 with a degree in Electronic Systems Engineering from the University of East Anglia. As a senior software engineer in the Business Systems and Development Group he manages the design of multimedia applications for training, reference and promotional activities. Martin has also been closely involved in the development of a number of expert systems and web-based software solutions. Clients have been drawn from the automotive and offshore industries, equipment and consumables suppliers and the Health & Safety Executive.
Jim Hamilton first became involved with non-destructive examination whilst with the UK Atomic Energy Authority at Dounreay. He then moved to Babcock Energy Research Centre in Renfrew where he worked on inspection systems development for the power industry. He joined Lloyd's Register in the mid-eighties and has been involved with a wide range of NDE activities in the marine, offshore and power sectors including training of LR surveyors in the basic NDE methods. He is presently involved in developing interactive CD and internet NDE training applications for LR.
Lloyd's Register is a multinational organisation with marine, industrial, offshore and transport interests, all of which involve weld radiography. Technical staff employed by Lloyd's Register are expected to be competent in materials and non-destructive examination (MNDE) which includes the interpretation of weld radiographs. As Martin Bourton and Jim Hamilton report, the staff receive training in the basic areas of MNDE and the training approach adopted includes the use of multimedia CD with an interactive element.
Multimedia CDs offer a cost-effective method of training. Their interactive nature provides a highly effective learning environment in terms of knowledge retention and significantly reduces the necessary study time, leading to lower training costs.
[1] From the student's perspective, the training becomes more personalised. The student can choose the time and place to study, selecting material relative to their particular needs. They can work at their own pace and receive constant feedback charting their progress via automatic testing built into the software.
This training CD on the subject of interpretation of weld radiographs has been developed in conjunction with TWI. The aims of the programme are to introduce the basic requirements for successful interpretation and to provide examples of weld defect images as generated by X-ray and gamma radiography. The CD consists of several sections, which may be accessed from a menu in any order and at any time allowing the student to move freely around the contents. In addition to photographic images, both audio commentary and text are used; audio to introduce sections and describe animations and text for more detailed descriptions within the sections.
The radiographic techniques section provides descriptions and animations to show how the technique used affects the appearance of the weld image on the radiographic film.
Assessment of film quality describes the checks necessary to ensure that the radiograph complies with various requirements and is suitable for assessment of the weld quality.
Weld quality is explained by means of images and descriptions of both external and internal weld features, which can appear on the radiographic image.
There is a tutorial section presented as an interactive question and answer session.
Finally, the student can undertake a self-assessment test of ten radiographs which gives a percentage success score and then permits review of the correct solution for each radiograph on completion of the test.
Radiographic techniques section
Access to the weld and geometry component dictate which radiographic technique should be used. This section describes the common techniques for plate and pipe butt welds and animations are used to show how the appearance of the weld image on the film changes with the position of the radiation source.
Animation is a particularly effective method of trans-ferring this knowledge as it can show both the movement of the radiographic source and the effect on the radiographic image simultaneously.
Single wall single image
With the single wall single image (SWSI) technique, radiation from the source passes through the weld and is recorded on the film. This technique is invariably applied for the radiography of plate butt welds and for the examination of pipe or vessel butt welds where access to inner and outer surfaces is available.
Panoramic
The panoramic technique is a version of SWSI where the source of radiation is positioned at the centre of a cylindrical component such as a pipe or vessel with the film wrapped around the outer surface of the weld. In this way the entire length of weld can be examined with one exposure. A single piece of film or a series of overlapping films may be used to cover the entire weld length. The three frames from the panoramic animation shown in Fig.1, illustrate the film being exposed, the removal of the film cassette and the resulting radiographic image.
Fig.1. Panoramic radiographic technique
Double wall double image
The double wall double image (DWDI) technique used for small diameter pipe welds, typically less than 90 mm outer diameter is described. The technique allows a weld to be examined in two or three exposures according to source placement. The animation ( Fig.2) shows how moving the radiation source allows both the upper and lower weld regions to be evaluated.
Fig.2. Double wall double image radiographic technique animation
Double wall single image
In the double wall single image (DWSI) technique radiation from the source passes through both walls of the component, but only the image of the weld region closest to the film is suitable for evaluation since the weld section nearest to the source appears blurred and distorted in the image. On larger diameter pipes, or if the source can be moved closer to the pipe surface the upper weld image can be moved completely off the film leaving the area of interest clear for evaluation, as seen in Fig.3 frame 3. Imparting this complex information without the use of animation would be both difficult and time-consuming.
Fig.3. Double wall single image radiographic technique
Alignment of radiation
The detection of planar defects such as cracks is sensitive to the radiation beam direction. This animation shows how alignment of the radiation beam changes the appearance of the defect in the image. Fig.4 shows an inclined crack that appears as a faint broad shadow in the radiograph. When the radiation is directed parallel to the plane of the crack, its image becomes darker and more sharply defined. However, when the radiation is directed obliquely to the plane of the crack the image becomes faint and may even eventually disappear as the angle of incidence increases.
Fig.4. Inclined crack animation
Requirements for viewing
There are several requirements when carrying out the viewing and interpretation of weld radiographs. These are described with the aid of photographs and audio commentary.
A prerequisite for satisfactory interpretation is that the interpreter must have adequate eyesight, whether corrected or uncorrected, and be able to recognise features in the image caused by various conditions.
The ability to recognise the features on a radiograph comes largely with experience. To assist in the interpretation of a radiograph the interpreter should be aware of the radiographic technique used and should have some knowledge of the weld configuration and welding procedure used. View-ing radiographs should be carried out using a film viewer in a darkened room. Care must be taken to avoid marking or damaging the film.
Film quality section
The interpretation process requires that film quality be of an acceptable standard so that weld quality can be assessed properly. In order to satisfy relevant codes and standards it is necessary that the stated requirements for radiograph identification, density and image quality sensitivity be achieved. This section discusses the monitoring of these parameters.
Radiograph identification
The labels required for identification of a typical weld radiograph are described. As a minimum the interpreter should be looking for job or component identity, location markers in the form of radiographic images and the date the radiograph was taken (
Fig.5). If all three elements are present the identification is deemed acceptable for the purpose of this exercise.
Fig.5. Radiograph identification screen with pop-up text annotation
Film density
The density or blackness of a radiograph affects the contrast of the image produced, contrast increasing with increasing density. For this reason minimum density requirements are specified in codes and standards. The influence of density on image quality is examined.
The section includes an interactive task where the student is asked to simulate the measurement of radiograph density using the mouse by pointing and clicking at selected points on the image. The student is expected to evaluate the acceptability of the densities displayed against prescribed criteria.
Radiographic sensitivity
This section examines how contrast and definition influence radiographic sensitivity and how the quality of the image can be evaluated through the use of image quality indicators. It highlights the importance of ensuring acceptable image quality. Different types of image quality indicators are described and an interactive presentation shows the effect of contrast and definition on the sensitivity of the radiographic image.
Film artefacts
Radiographs can sometimes be misinterpreted due to images appearing on the radiograph that are not associated with the weld. These indications, referred to as artefacts, can be due to handling damage or film processing faults. Those due to film damage may sometimes be identified by viewing under reflected light. This section presents some of the more commonly encountered artefacts.
Figure 6 shows a radiograph having an artefact caused by the presence of static electricity.
Fig.6. Static electricity film artefact
Weld quality section
Having established that film quality is acceptable, the radiograph can then be examined for the presence of defects in the weld. Both surface and internal weld features appear in the image and can be assessed.
Weld surface features
Common weld surface conditions that can appear in the radiograph are described and shown as both photographic and radiographic images. When a condition is selected from the weld surface features list, a detailed description is presented together with a photograph or diagram and thumbnails of radiographic examples ( Fig.7).
Fig.7. Excessive root penetration screen design showing a photograph of the condition and two radiographic examples
Clicking on a thumbnail image displays the full screen radiograph including detailed information relating to the weld itself ( Fig.8).
Fig.8. Excessive root penetration
Weld defects
This section shows a few of the many possible radiographic images produced by internal weld defects. Examples are described using diagrams, photographs and radiographic images. As in the weld surface features section, selection of an item from the list displays a detailed description ( Fig.9) and clicking on a thumbnail ( Fig.10) shows the full screen view of the radiograph ( Fig.11).
Fig.9. Weld cracking screen design 1
Fig.10. Weld cracking screen design 2
Fig.11. Weld cracking radiograph
Tutorial chapter
The tutorial presents a series of interactive questions that require the student to demonstrate the extent of knowledge gained from the CD. Answers are revealed or solutions provided on completion of each question. Fig.12 shows a graphical multi-choice question in which the student must select the schematic that most closely applies to the weld radiograph. The interactive nature of the question and answer session reinforces the information presented earlier in the course and aids memory retention.
Fig.12. Tutorial multi-choice question
Assessment chapter
The self-assessment section consists of ten radiographs, each contains one or more examples of weld defects which have been described elsewhere in the CD. The radiographs are presented as shown in Fig.13.
The student can select a radiograph to examine by clicking on a thumbnail. This presents the image together with a list of possible weld defect conditions ( Fig.14).
Fig.14. Assessment question
The radiograph can be examined in more detail by clicking on the magnify icon which presents a full screen image including details of the weld ( Fig.15).
Fig.15. Full screen weld radiograph
A further magnification stage of about double size is available and because the image is larger than full screen, the image can be 'dragged' around the screen to allow close up examination of any particular area.
By selecting the appropriate defects from the defect list ( Fig.14) and clicking on the 'submit' button, the ten thumbnails are again displayed. Radiographs already submitted appear faint to indicate that they have been answered. It is possible to reselect an answered radiograph and change the submission. Another useful feature of the programme allows the student to review any other section of the CD during the assessment and then return to complete the assessment.
On completion of the ten radiographs the student is presented with a percentage score and success or otherwise for each radiograph is indicated. It is now possible to re-examine each of the radiographs and to review the correct solutions for each of the images by clicking on the 'view correct answers' button that has become available on the defect list screen on completion of the assessment.
The assessment process has been designed as a formal examination with the correct answers revealed to the user only upon completion of all ten questions. Then the student is prompted to review their performance and revisit the areas that require further study. This automatic feedback tailored for each student provides a personalised 'to-do' list that enables effective study focused on the topics requiring further work.
Future developments
The layout of the programme allows for the possibility of expanding the number of examples of weld radiographs in future versions to further enhance the educational content. Further work is in progress that will use the display techniques devised for the CD to develop a method of assessing student competence in radiographic interpretation of welds remotely by means of the Internet.
Conclusions
This training programme is considered suitable as an introduction to the subject of interpreting weld radiographs and is presented in a form that allows the student to interact with the material and study at their own pace. By presenting the information in an interactive form the student gains experience of the appearance of welds and weld features as they explore the programme in addition to learning the importance of viewing procedure and film quality.
The CD has been well received by technical staff within Lloyd's Register and has been used both to prepare students prior to attending the initial training course in Materials and Non-Destructive Examination and as a refresher aid for the five yearly re-qualification examinations which the staff are required to undertake.
The CD is now available from TWI at a cost of £499 plus VAT. Contact Martin Bourton.
Email: martin.bourton@twi.co.uk for further information.
Reference
| N° | Author | Title |
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| 1 | Bourton M A, Howarth D and McFarlane I: | 2000. 'A teaching discovery - multimedia training in basic metallurgy and welding - at your PC', Bulletin, 41 (2). | Return to text |
