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Monitoring structural integrity by acoustic emission
CONFERENCE REPORT 12th Annual Conference of the Non-Destructive Testing Society of Great Britain Cardiff, UK, 9-12 September 1975
The last conference of the NDT Society before it changes its name to the British Institute of Non-Destructive Testing completed an important phase of the twenty one years of the society's history in a town where recently everything has acquired two names. The rapid expansion of ndt in these twenty one years seemed to be continuing unabated as lecturers described achievements and faced the problems of the future in the lecture halls of the Anatomy Department on Park Place or FFordd Y Parc as it is alternatively labelled. E. J. Gdmwade of Kodak Ltd gave the most comprehensive review of the history of the society and its subject in his entertaining president's honour lecture. He quoted Lewis Carors Old Father William, presumably to celebrate the society's new maturity although the reference to standing on one's head also describes the overturning of ideas and trends in the rapid development on ndt. His long experience in teaching lead him to comment of ndt education and to call for continuing assessment of inspectors. This proposal echoed an earlier lecture by A. R. Bond of British Airways who warned that rapid technical change would make it difficult for today's engineers to keep up and if he does to prove it to an employer. Warnings are very much in the spirit of the times and C. D. Wells of Wells Krautkramer managed to shake complacency and composure in equal measure in his hardhitting talk on the state of the industry. He told delegates that the ndt service industry has a difficult task with undercapitalized firms using and looking after a wide range of equipment which is constantly superseded and yet still leaves old equipment to be supplied with spare parts. The industry and ndt, he felt, was not helped by user companies duplicating work by making their own equipment where it was available already without waste of the firm's resources outside its real field of business. Nor is the industry helped by the plethora of schemes of training and of standardization and of the expert poaching which follows. The discussion which followed such an individualistic view was understandably intense but others such as R. Sharpe of the NDT Centre, Harwell, drew back the curtain on the future as a remedy to present worries. Not that the future does not hold out worries of its own. H. C. Cotton of BP Ltd, gave an amusing talk on the near future and the recent past of the ndt on the North Sea. He described the dangers and difficulties of inspecting enormous structures in,deep water and told delegates that while BP was studying fracture mechanics as a guide to inspection and survailance, the guiding philosophy remained 'build it right first time'. In an unscheduled appearance, however, J. C. Walter of det Norke Veritas, answered the much-quoted figure of 15 million inspectors required for North Sea work by telling
340
delegates that 640 trained men could inspect all the rigs in the North Sea in 1980 using a clean-up and magnetic-particle testing procedure developed in Norway. The writers of the original report were not able to answer this as their paper was withdrawn to preserve confidentiality. The novel approach for the North Sea is, however, on the drawing board. V. A. Peters and C. J. H. Webborn of the British Steel Corporation described developments to fit acoustic emission out for sea to overcome the odds. And novelty is not lacking on dry land either. D. Birchon of the Admiralty brought everyone up to date on acoustic emission and explained that he used the term instead of stresswave emission because of its all-embracing simplicity. This journal prefers the term incidentally because it saves keeping those wretched hyphens in order. Still on dry land, P. A. Lloyd, of Chelsea College, described work on impact analysis at Harwell which has decked out the wheel tapper's art to become a novel technique again. This work has gone beyond efforts in the motor industry to give good correlation for bonded systems. W. West of AERE Harwell introduced a new development in radiography which harnesses the properties of the proton. Protons can give radiographs which highlight boundaries in objects, and also by use of their marginal range can give very sensitive radiographs of a narrow layer of an object. J. McKelvie of the University of Strathclyde also broke new ground with an optical grid which will deform with a test object and can be replicated and analysed to show the residual stress. This method has been used on an oil rig, of course, and could prove a way of bringing stress analysis into the mainstream of ndt. The mainstream of ndt has also managed to flow past concrete testing for some time but two papers showed that this would not remain so much longer. S. A. Robertson of Testconsult Ltd showed how sonic testing and vibration testing can test concrete piles cheaper than old methods of static loading. H. N. Tomsett of the Cement and Concrete Association showed how ultrasonics can be used to measure strength of concrete and told delegates that it is used now to inspect workmanship and materials more and more. Ultrasonics is also moving forward quite apart from concrete testing. M. G. Silk described NDT Centre work to improve accuracy of ultrasonic measurement of defects to keep up with fracture mechanics. It uses elapsed-time techniques for greater precision but work on improving current techniques and data enhancement are also yielding results so that accuracies approaching 0.1 mm have been approached. A. G. Julier of Well-Krautkramer Ltd, G. R. O. Shaw and P. D. Hanstead of the Central Electricity Generating Board, all gave lectures in an ultrasonic tutorial session to show that there is still plenty of life left in what have already become traditional techniques. Industry is the subject of ndt and industry each industry has its own specialized type of ndt. H.J. Meyer of MAN
NON-DESTRUCTIVE TESTING. DECEMBER 1975
AG, Germany, has obtained accuracies that might even surprise Dr Silk, in his efforts to measure thickness of zirconium fuel channels for the nuclear industry. A weighted probe with knife-edged ring to retain couplant gave accuracies to 0.01 mm for 1.5 mm thick Zr sheet. Mr Meyer's fellow countryman, W. Stumm, of Institut Dr F6rster, described the far-reaching work in bringing electromagnetic inspection to help mass production. This year's revelations include a machine to magnetize square billets, register stray flux on an endless loop of magnetic tape and scan this tape to find surface defects at high speed. E. Fretwell, of TI Chesterfield, caught the attention of delegates with his description of ultrasonic and gamma gauging built into a line for steel seamless cylinders for gas holding. The simplicity and thoroughness of the system for mass production is an impressive testimonial to ndt's place in industry. B. Jennings of TI Tube Products kept his company's flag .high with a contribution on eddy-current testing of longitudinal welded tubes up to 38 mm diameter. The speed of welding (0.5 ms "1) has meant that eddycurrents have taken over from visual inspection. Two other papers by L. L. Davies of GKN Ltd and J. D. McMillan of Babcock & Wilcox Ltd also dealt with metal testing. L. L. Davies in particular stressed the benefits to industry of ndt to ensure a sound product. Meanwhile standards came under scrutiny by B. Lambert of Non-Destructive Testers Ltd and J. G. Young of the
Welding Institute as they described the problems of following them and keeping up with them respectively. G. Oates of the CEGB and S. Wise of British Rail describe ndt in two basic industries: electricity generation and railways. Aerospace has become known for the vigour of the NDT Society Group which studiesits ndt side. This reputation was enhanced by contributions by J. W. Purvis of Boeing Aeroplane Co on the Boeing 707 and P.A.E. Stewart of Rolls-Royce Ltd on x-radiography of engines under power. A contribution by D. M.. Forney of the United States Airforce Materials Laboratory gave delegates an insight into the vast effort on ndt by the USAF. The 200 or so delegates at the conference were kept busy by the round of lectures and visits. The RAF played host to those interested in aerospace work for a technical visit to St Athan airfield one afternoon. More general interests were satisfied by an evening out at Unit Inspection at Sketty Hall where Mr Webborn entertained everyone with an evening of technical display, good food and traditional Welsh singing to the accompaniment of the harp. The conference dinner, on the other hand had no harps and no technical content whatsoever, but provided connoisseurs of the after-dinner speech with a rate delight. The conference was altogether a heartening display of technical progress delivered with wit and skill.
D. Brocklesby
NEW PUBLICATIONS Monitoring structural integrity by acoustic emission J. C. Spanner, J. W. McEIroy editors, ASTM STP 571, ~20 This volume is a companion to the widely read ASTM STP 505 on acoustic emission. It is significant that the new collection of papers focusses on the application of acoustic emission techniques to industrial problems; rather than just describing the phenomenon and the systems used in detection. As a general aid to people entering the field the bibliography compiled by DrouiUard is invaluable, this contains a list of 412 references covering the period 1970-1972. These references are cross indexed both for authors and contents and enables rapid identification of relevant work. It is to be hoped that this bibliography will be extended and updated. In the introductory paper Schofield poses the question 'why acoustic emission?' - a question often voiced by industry. As a reply he answers with the question - 'why not?' and explains a significant part of the reason for industry's lack of initiative in taking advantage of the capabilities of ae is the problem of explaining the implications of ae data to higher management. A large proportion of the effort in ae testing has gone into the monitoring of pressurised components. The reason for this is twofold, firstly pressurised components are easy to test and in many cases proof pressurisations are already undertaken; secondly, these can be components which be-
NON-DESTRUCTIVE TESTING . DECEMBER 1975
cause of financial or safety considerations cannot be allowed to fail. Many of the contributers discusss the testing of pressure vessels and pressurised components. Perhaps the most ambitious aim is the on-line, in-service monitoring of a reactor pressure vessel. Westinghouse is pursuing this objective and Raj Gopal describes its approach to the problem. Parry from EXXON also describes some work on reactor pressure vessels. One of the attractions of acoustic emission is the vast range of materials that can be investigated; metals, composites, rocks and concrete are all mentioned in the text. Indeed Hardy has an extensive contribution on the application of ae techniques to rock mechanics. The mechanisms giving rise to emission activity were mainly covered in the original volume but more recent work on frequency analysis and phase transformation is described in the new publication. The hope for frequency analysis is that it will enable emission sources to be identified. Emissions generated during phase transformation are important as they will occur in the heat affected zones of welds; the identification of poor welding by ae techniques is perhaps one of the areas with the greastest potential impact on ndt methods.
341
The last conference of the NDT Society before it changes its name to the British Institute of Non-Destructive Testing completed an important phase of the twenty one years of the society's history in a town where recently everything has acquired two names. The rapid expansion of ndt in these twenty one years seemed to be continuing unabated as lecturers described achievements and faced the problems of the future in the lecture halls of the Anatomy Department on Park Place or FFordd Y Parc as it is alternatively labelled. E. J. Gdmwade of Kodak Ltd gave the most comprehensive review of the history of the society and its subject in his entertaining president's honour lecture. He quoted Lewis Carors Old Father William, presumably to celebrate the society's new maturity although the reference to standing on one's head also describes the overturning of ideas and trends in the rapid development on ndt. His long experience in teaching lead him to comment of ndt education and to call for continuing assessment of inspectors. This proposal echoed an earlier lecture by A. R. Bond of British Airways who warned that rapid technical change would make it difficult for today's engineers to keep up and if he does to prove it to an employer. Warnings are very much in the spirit of the times and C. D. Wells of Wells Krautkramer managed to shake complacency and composure in equal measure in his hardhitting talk on the state of the industry. He told delegates that the ndt service industry has a difficult task with undercapitalized firms using and looking after a wide range of equipment which is constantly superseded and yet still leaves old equipment to be supplied with spare parts. The industry and ndt, he felt, was not helped by user companies duplicating work by making their own equipment where it was available already without waste of the firm's resources outside its real field of business. Nor is the industry helped by the plethora of schemes of training and of standardization and of the expert poaching which follows. The discussion which followed such an individualistic view was understandably intense but others such as R. Sharpe of the NDT Centre, Harwell, drew back the curtain on the future as a remedy to present worries. Not that the future does not hold out worries of its own. H. C. Cotton of BP Ltd, gave an amusing talk on the near future and the recent past of the ndt on the North Sea. He described the dangers and difficulties of inspecting enormous structures in,deep water and told delegates that while BP was studying fracture mechanics as a guide to inspection and survailance, the guiding philosophy remained 'build it right first time'. In an unscheduled appearance, however, J. C. Walter of det Norke Veritas, answered the much-quoted figure of 15 million inspectors required for North Sea work by telling
340
delegates that 640 trained men could inspect all the rigs in the North Sea in 1980 using a clean-up and magnetic-particle testing procedure developed in Norway. The writers of the original report were not able to answer this as their paper was withdrawn to preserve confidentiality. The novel approach for the North Sea is, however, on the drawing board. V. A. Peters and C. J. H. Webborn of the British Steel Corporation described developments to fit acoustic emission out for sea to overcome the odds. And novelty is not lacking on dry land either. D. Birchon of the Admiralty brought everyone up to date on acoustic emission and explained that he used the term instead of stresswave emission because of its all-embracing simplicity. This journal prefers the term incidentally because it saves keeping those wretched hyphens in order. Still on dry land, P. A. Lloyd, of Chelsea College, described work on impact analysis at Harwell which has decked out the wheel tapper's art to become a novel technique again. This work has gone beyond efforts in the motor industry to give good correlation for bonded systems. W. West of AERE Harwell introduced a new development in radiography which harnesses the properties of the proton. Protons can give radiographs which highlight boundaries in objects, and also by use of their marginal range can give very sensitive radiographs of a narrow layer of an object. J. McKelvie of the University of Strathclyde also broke new ground with an optical grid which will deform with a test object and can be replicated and analysed to show the residual stress. This method has been used on an oil rig, of course, and could prove a way of bringing stress analysis into the mainstream of ndt. The mainstream of ndt has also managed to flow past concrete testing for some time but two papers showed that this would not remain so much longer. S. A. Robertson of Testconsult Ltd showed how sonic testing and vibration testing can test concrete piles cheaper than old methods of static loading. H. N. Tomsett of the Cement and Concrete Association showed how ultrasonics can be used to measure strength of concrete and told delegates that it is used now to inspect workmanship and materials more and more. Ultrasonics is also moving forward quite apart from concrete testing. M. G. Silk described NDT Centre work to improve accuracy of ultrasonic measurement of defects to keep up with fracture mechanics. It uses elapsed-time techniques for greater precision but work on improving current techniques and data enhancement are also yielding results so that accuracies approaching 0.1 mm have been approached. A. G. Julier of Well-Krautkramer Ltd, G. R. O. Shaw and P. D. Hanstead of the Central Electricity Generating Board, all gave lectures in an ultrasonic tutorial session to show that there is still plenty of life left in what have already become traditional techniques. Industry is the subject of ndt and industry each industry has its own specialized type of ndt. H.J. Meyer of MAN
NON-DESTRUCTIVE TESTING. DECEMBER 1975
AG, Germany, has obtained accuracies that might even surprise Dr Silk, in his efforts to measure thickness of zirconium fuel channels for the nuclear industry. A weighted probe with knife-edged ring to retain couplant gave accuracies to 0.01 mm for 1.5 mm thick Zr sheet. Mr Meyer's fellow countryman, W. Stumm, of Institut Dr F6rster, described the far-reaching work in bringing electromagnetic inspection to help mass production. This year's revelations include a machine to magnetize square billets, register stray flux on an endless loop of magnetic tape and scan this tape to find surface defects at high speed. E. Fretwell, of TI Chesterfield, caught the attention of delegates with his description of ultrasonic and gamma gauging built into a line for steel seamless cylinders for gas holding. The simplicity and thoroughness of the system for mass production is an impressive testimonial to ndt's place in industry. B. Jennings of TI Tube Products kept his company's flag .high with a contribution on eddy-current testing of longitudinal welded tubes up to 38 mm diameter. The speed of welding (0.5 ms "1) has meant that eddycurrents have taken over from visual inspection. Two other papers by L. L. Davies of GKN Ltd and J. D. McMillan of Babcock & Wilcox Ltd also dealt with metal testing. L. L. Davies in particular stressed the benefits to industry of ndt to ensure a sound product. Meanwhile standards came under scrutiny by B. Lambert of Non-Destructive Testers Ltd and J. G. Young of the
Welding Institute as they described the problems of following them and keeping up with them respectively. G. Oates of the CEGB and S. Wise of British Rail describe ndt in two basic industries: electricity generation and railways. Aerospace has become known for the vigour of the NDT Society Group which studiesits ndt side. This reputation was enhanced by contributions by J. W. Purvis of Boeing Aeroplane Co on the Boeing 707 and P.A.E. Stewart of Rolls-Royce Ltd on x-radiography of engines under power. A contribution by D. M.. Forney of the United States Airforce Materials Laboratory gave delegates an insight into the vast effort on ndt by the USAF. The 200 or so delegates at the conference were kept busy by the round of lectures and visits. The RAF played host to those interested in aerospace work for a technical visit to St Athan airfield one afternoon. More general interests were satisfied by an evening out at Unit Inspection at Sketty Hall where Mr Webborn entertained everyone with an evening of technical display, good food and traditional Welsh singing to the accompaniment of the harp. The conference dinner, on the other hand had no harps and no technical content whatsoever, but provided connoisseurs of the after-dinner speech with a rate delight. The conference was altogether a heartening display of technical progress delivered with wit and skill.
D. Brocklesby
NEW PUBLICATIONS Monitoring structural integrity by acoustic emission J. C. Spanner, J. W. McEIroy editors, ASTM STP 571, ~20 This volume is a companion to the widely read ASTM STP 505 on acoustic emission. It is significant that the new collection of papers focusses on the application of acoustic emission techniques to industrial problems; rather than just describing the phenomenon and the systems used in detection. As a general aid to people entering the field the bibliography compiled by DrouiUard is invaluable, this contains a list of 412 references covering the period 1970-1972. These references are cross indexed both for authors and contents and enables rapid identification of relevant work. It is to be hoped that this bibliography will be extended and updated. In the introductory paper Schofield poses the question 'why acoustic emission?' - a question often voiced by industry. As a reply he answers with the question - 'why not?' and explains a significant part of the reason for industry's lack of initiative in taking advantage of the capabilities of ae is the problem of explaining the implications of ae data to higher management. A large proportion of the effort in ae testing has gone into the monitoring of pressurised components. The reason for this is twofold, firstly pressurised components are easy to test and in many cases proof pressurisations are already undertaken; secondly, these can be components which be-
NON-DESTRUCTIVE TESTING . DECEMBER 1975
cause of financial or safety considerations cannot be allowed to fail. Many of the contributers discusss the testing of pressure vessels and pressurised components. Perhaps the most ambitious aim is the on-line, in-service monitoring of a reactor pressure vessel. Westinghouse is pursuing this objective and Raj Gopal describes its approach to the problem. Parry from EXXON also describes some work on reactor pressure vessels. One of the attractions of acoustic emission is the vast range of materials that can be investigated; metals, composites, rocks and concrete are all mentioned in the text. Indeed Hardy has an extensive contribution on the application of ae techniques to rock mechanics. The mechanisms giving rise to emission activity were mainly covered in the original volume but more recent work on frequency analysis and phase transformation is described in the new publication. The hope for frequency analysis is that it will enable emission sources to be identified. Emissions generated during phase transformation are important as they will occur in the heat affected zones of welds; the identification of poor welding by ae techniques is perhaps one of the areas with the greastest potential impact on ndt methods.
341