Non-destructive testing (NDT) is a discipline within engineering dedicated to the detection and evaluation of defects in materials.  A closely related technology is condition monitoring (CM) which is concerned with operating machinery.  Defects and damage affect the serviceability of materials, structures and equipment and can lead to loss of strength and/or failure in service.  For highly stressed structures, NDT/CM may be critical to ensuring safe operation.  These technologies also find application in quality control and the assessment of deterioration of operating plant. The defects and damage may be cracks or inclusions in metal welds and castings; cracking or debonding or delaminations in composites; or variations in structural properties.  The essential feature of NDT is that the process produces no deleterious effects on the material or structure under test.

Non-destructive evaluation has three major functions:

1. Initial inspection of test specimens  or  confirmation of the structural integrity of new components,
2. Monitoring sample tests in progress  or  components subjected to service loads,
3. Analysing test results after failure  or  proof loading of components during their service life.

1. electromagnetic (radiography, light, heat, microwaves, eddy current, dielectric and electric).
2. chemical spectroscopy (ultra-violet, Raman, infra-red, electron spin resonance and nuclear magnetic resonance), and
3. mechanical vibration (acoustic microscopy, ultrasonics, acousto-ultrasonics, acoustic emission and coin-tap or wheel-tap vibration)

However, only a limited number of techniques have been adapted for use under water.  Some NDT techniques are amenable to data presentation in a 3-D format known as tomography.  NDT methods may be used to ascertain global integrity or to examine local problems and many techniques can be automated.  For further specific  information, see the Teaching Support Material on Non-destructive testing of advanced composites for the BEng (honours) Mechanical Engineering with Composites students.

The professional institute for this technical area is the British Institute of Non-Destructive Testing (BINDT) which:

• offers Engineering Council registration,
• publishes a monthly journal: Insight,
• hosts the PCN (Personnel Certification in Non-destructive testing) Certification Scheme for NDT practitioners including approval of personnel to carry out non-destructive tests in the context of the European Pressure Equipment Directive (97/23/EC),
• is licensed by the Engineering Council to operate a scheme for the Licensing of Competent Persons in the field of non-destructive testing (NDT), and
• hosts the the International Association of Quality Practitioners (IAQP).

Resources:

• Seeing is believing: basic ultrasonics, Services Sound and Vision Corporation (Ministry of Defence), 1987. UoP Library Shelfmark: AV 620.11274 SEE (7-day loan).  This VHS videocassette uses Schlieren photography to visualise ultrasound pulses travelling in a glass block - HIGHLY RECOMMENDED.

References:

• M Bayliss, D Short and M Bax, Underwater inspection, Spon, 1988. ISBN 0-419-13540-5.  UoP Library.
• AA Carvalho, IC Silva, JMA Rebello, RO Carneval and JAB Farias, Inspection of ship hulls using automated underwater inspection, Insight, December 2005, 47(12), 744-747.
• VD Davey, O Førli, GA Raine and R Whillock, Non-Destructive Examination of Underwater Welded Structures, Woodhead Publishing, Cambridge, 1999.  ISBN-13: 978-1-85573-427-2.
• O Førli and GA Raine, NDT offshore: a review of current practice, Insight, June 1996, 38(6), 399-405+411.
• J Summerscales, Non-destructive testing of advanced composites: a review of recent advances, British Journal of Non-Destructive Testing, November 1990, 32(11), 568-577. Restricted: Download 2.25MB .doc file. This version has additional images.
• J Summerscales, Manufacturing Defects in Fibre Reinforced Plastics Composites, Insight, December 1994, 36(12), pp 936-942. Restricted: Download 73KB .doc file.