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Title: Some aspects of modern arc welding
Author: Glover, T. S.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1934
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Abstract:
In the X-ray examination, good specimen welds, with the surface machined down to the level of the plate, show little difference in intensity between the seam and the base metal. These are relatively uninteresting in reproduction and are very seldom used for publication, with the inevitable result that distrust of the welding process is developed in the reader's mind. The wide field of the applications of welding in the workshop makes it necessary to consider each X -ray test separately, and it will not be found possible to utilise this method of testing in each case. With certain complicated structures - for example, those shown in photographs Nos. l and 2 - a compromise might be effected, but the results of the tests carried out on a portion of the work could not be assumed to be typical of the whole. If an X-ray test is to be carried out, it must be done systematically throughout every inch of the weld, because although one can assume that variations under normal working conditions will be slight with modern machines and well trained welders, risk of serious failure at this stage of the development of arc welding would mean a severe setback to the process. It would be unfortunate if this were to happen at this time because of the recent developments with reference to high pressure work, in boilers and pipe lines, where the X-ray inspection will prove invaluable as a non-destructive test. The normal test pressure, exceeding the working pressure by say 50-100 per cent, might or might not show up any weakness in the joint in its single application. The incipient flaw would probably lie unnoticed until its fatigue resistance was reduced to dangerous limits, when the result might mean serious loss of life. In the first Report of the Steel Structures Research Committee, the X-ray method of fault detection is referred to as being "of undoubted value in the laboratory for the detection of faults in specimen welds, with a view to tracing their causes and so developing an improved technique, but the somewhat extravagant claims put forward by some investigators require qualification". So far as the testing of welds in structures is concerned, where the joints are complicated and extremely difficult to photograph with any success this statement may be true. Longitudinal seam welds, on the other hand, which in pressure vessels are generally a line of weakness, can be easily adapted for testing, and films up to 18 inches in length can be used for one exposure. As a general rule with modern equipment 15 inch films are used both for longitudinal and circumferential seams. With a film length of fifteen inches, where accurate results are necessary, the photo-electric cell could be adapted to deal with these films quickly and positively. The day may not be very far distant when, after development of the X-ray film, the negative showing the seam weld will be passed through a similar apparatus to this which will either arrest the passage of the film in the region of the flaw, or graph out the variations on paper so that the operator can more readily observe these. This instrument will have to be capable of examining an extremely narrow band across the weld with minute accuracy, and respond to small changes in density. When this is achieved, X-ray examinations of welded joints will be vastly simplified and the semi- skilled labour necessary will show a saving in cost. By that time further experiments lining up the physical properties of the weld with the X-ray negative will have been carried out. The heavy initial cost of the modern portable foolproof X-ray apparatus, and the expensive nature of the test, limits the application to work whose price can carry this extra overhead cost. Naturally where prices are being cut in the market, due to severe competition, the extra expense of such a test would be an unnecessary burden which no manufacturer could be expected to undertake under present conditions of trade. The lengthy nature of the test also tends to increase overhead charges on the work by delaying its progress through the workshops. For these reasons the application of X-ray testing at the present time is limited, but as this is the only positive non-destructive test which is really reliable, development will be necessary. It cannot be expected that this method will supersede metallurgical and mechanical tests, but if combined with them it will help to shed light on practical difficulties and problems which undoubtedly exist. Considering the arc welding process from all points of view one is impressed with the feeling that further advance is largely dependent on psychological factors rather than on the practical details. The lack of confidence is one great barrier that must be overcome, and there is also a repugnance to adopt what may be regarded as unorthodox methods. The cry of the opponents has always been "It all depends on the lder" but development has been so rapid in the manufacture and improvement of welding electrodes and machinery that the process is becoming more and more purely mechanical and less dependent on the personality of the operator.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.651548  DOI: Not available
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