BSI fights electrical burns in a mixed bag of ndt standards

BSI fights electrical burns in a mixed bag of ndt standards

The final afternoon started with a paper by M. F. Markham (National Physical Laboratory) on characterisation of defects by ultrasonics. In one method ...

153KB Sizes 0 Downloads 34 Views

The final afternoon started with a paper by M. F. Markham (National Physical Laboratory) on characterisation of defects by ultrasonics. In one method (c - scan) the attenuation of the wave is scanned over the surface of a plane sheet immersed in water. An extension of the technique permits a cylinder to be checked by mounting it on rollers and placing a reflector within it. Under development is a method of ultrasonic spectroscopy; the amplitude and frequency profile of a pulse is influenced by the presence of defects, and a discrimination can readily be made between areas of wilds and areas of delamination. These methods offer an immediate check on the quality of composite mouldings. The next paper by J. H. Speake and G. J. Curtis (Nondestructive Testing Centre, Harwell) described both ultrasonic and sonic emission NDT of polymer adhesives. Ultrasonics are used primarily to characterise the epoxide adhesive by measurement of elastic moduli when cured. shear moduli can also be checked by using a torsion pendulum. A third method of checking employs measurements on a reflected ultrasonic wave, made over a range of temperatnre, to reveal an undercured condition. The sonic emission teclmique records the sounds at ultrasonic fl-equency which have been found to be emitted by composite materials when strained. A model lap joint has been investigated, and il is found that thicker and weaker glue joints emil a greater total sound energy. Emission during crack growth is now being studied. The last talk was by G. D. Sims {National Physical Laboratory) who discussed stress wave emission from polymeric materials. A compact and cheap equipment has

been developed using a single channel system to count sound emissions generated by microfailure events. This provides simple but adequate information for many purposes. Examples were given of the quiet behaviour found for polypropylene reinforced with untreated glass fibres, and of the contrasting high emission prior to yielding for polypropylene with coupled glass fibres, the latter giving early warning of failure. The method is also being applied to laminated cross-ply materials, where correlations with structural studies and mechanical data nray form the basis of proof test procedures and in-service monitoring. An extra paper wtfich will be included in the conference proceedings is by R. J. Cook and R. G. Jones (National Physical Laboratory) on the development of new techniques/'or the measurement of electrical permittivity and loss angle in the frequency range 30 MHz to 140 GHz, With these techniques it is now possible to measure very low loss materials at one extreme, and anisotropic high loss materials at the other. In this short account of the work presented there has not been space to elaborate on the quality control possibilities. Although most of the techniques described could be of use in this field, further development would be required to simplify and cheapen the equipment for a particular application. The Conference organisers hope that such development will follow when producers and processors have access to the proceedings which are to be published in 1975. Perhaps of most immediate general application are the techniques of differential scanning calorimetry, holography and ultrasonic testing. K. Thomas

N E W PUBLICATIONS BSI fights electrical burns in a mixed bag of ndt standards The new British standard, BS 5138: 1974, for magnetic particle testing was released last October. The full title is British Standard Specification for magnetic particle flaw inspection of finished, machined, solid, forged and drop stamped crankshafts. The standard is for crankshafts with pin or journal final diameter of 80 mm excluding built-up shafts and motor-vehicle shafts. It covers any shaft proportioned in accordance with the rules of Lloyd's Register of Shipping. The cleaning, magnetization, and flaw indication are all specified. In particular the standard insist that the shafts are magnetized for longitudinal and transverse defects. The use of prods is ruled out except by prior agreement of the buyer. This stipulation is to protect the shaft from burn marks. The British Standards Institution has added another part to BS 4331 : assessing the performance characteristics of ultrasonic flaw detection equipment. This part, Part 3, covers the in-service monitoring of probes other than those for immersion testing. The first two parts were concerned with the performance of the flaw detector while this one is confined to probe characteristics. It covers beam angle,

N O N - D E S T R U C T I V E T E S T I N G . A P R I L 1975

probe index, beam profile, main frequency, ultrasonic field zones and signal to noise ratio. It makes recommendations on the frequency to be used during performance checks. A further standard, BS 5179 presents a guide to the operation and evaluation of quality assurance systems. It suggests three systems which rationalize evaluation for most buyers at three levels of increasing complexity. The systems are concerned chiefly with industrial purchasing. Part 1 reconnnends minimum standards for suppliers inspection to buyers specification, Part 2 details the inspection systems which can be applied and Part 3 makes recommendations for a suppliers quality control system. The standard is intended to be practical compared with the more theoretical treat ment of quality assurance in BS 4891:1972. The BSI has published three other standards of interest to inspects for transportable gas containers, magnifiers and steam turbines. BS 5945 Part 2 covers steel containers for gas, up to 130 1 capacity, with automatic circumferential welds. This was prepared at the request of the Home Office

75

for the requirements of proposed laws on gas transport. The Home Office has said it would not object to requests to use of the road for transport of gas in containers to this standard. BS 5165 is a guide to the selection of low-power mangiflers for visual inspection. It corresponds to international standard ISO 3058:1974 non-destructive testing. The standard was written to improve the selection of magnifiers in inspection. BS 752 is a test code for acceptance of steam turbines and is a new edition of an old standard. Much of the code has been completely rewritten. A new section covers steam quality which has become important now that some power stations use steam from nuclear reactors. BSI, 2 Park Street, London WIA 2BS,

UK

Manual gives energetic x-ray hints A 40-page manual recently published gives a practical guide to industrial radiographers who use linier accelerators.

76

It is published by Varian but much of what it contains applies to all accelerators and not just Linatron equipment. It gives illustrated information on the radiography of heavy steel sections and for solid propellant; Linatrons were first used for radiography of rockets. There is a selection of typical exposure curves which could be useful. Varian,

Radiation Division, 611 Hansen Way, Palo Alto, California 94303, USA

Philosophy is free K. J. Law associates of Detroit has published a six-page free booklet: The Philosophy of eddy-current testing. This booklet covers the principles of the method and naturally advocates its wider use. It discusses influences on test results and the choice of transducer. There is a wide bibliography. K. J. Law Associates Inc, 26325 WestEight

Mile, Detroit, Michigan 48240, USA

NON-DESTRUCTIVE

T E S T I N G . A P R I L 1975