In the present work, ultrasonic and radiographic techniques have been employed on woven fabric glass-epoxy, carbon-epoxy, glass- phenolic, carbon-phenolic and three dimensional preform made glass-furfuryl alcohol based phenolic laminates and cylindrical liner of smaller diameter of high silica glass-phenolic bonded and unbonded to aluminium casing to study the various defects in them. Glass-phenolic, carbon-phenolic and three dimensional glass furfuryl phenolic composites which are generally of porous in nature and highly attenuative, did not reveal any defects by PET because ultrasonic energy got scattered in propagation, whereas in glass-epoxy and carbon-epoxy defects can be sized. Drycoupling did not suffer from the above problems in identifying the presence of the defects in all the above composites whereas sizing cannot be done because the technique itself offers limitation. X-ray radiography taken at x, y and z directions on representative composite specimens revealed defects in weaving pattern, porosity, delaminations and foreign inclusions.

The multiple delaminations in a high silica glass-phenolic cylindrical liner of smaller diameter can be detected by X-ray radiography. The geometry, multiple delaminations, porosity of the liner creates problems for using PET because the couplant seeps through the liner, geometry does not allow the probes to sit properly. The use of drycoupling eliminates the problem of couplant, the smaller probes sit properly on the liner but because of the multiple delaminations the ultrasonic energy is highly attenuated. The use of radiography in the present case solves the problems of couplant and geometry, as the technique is a non-contact one and radiograph gives the visual image record of the multiple delaminations. If the liner is bonded inside to an aluminium casing, the delectability of disbond (between the aluminium casing and the liner) and delaminations (within the liner) creates more problems to both ultrasonic drycoupling and PET. The detection of disbond and delamination together present at a single location offers more complexity to drycoupling and PET and finally the detection becomes impossible. The detection becomes further worse as the other side of the liner (i. e. from inner side of the line) is inaccessible. The use of radiography offers solutions to all these problems such as porosity, geometry, couplant problem and inaccessibility from the other end. The detection of disbond and delamination together has been detected by X-ray radiography. If the casing is a maraging steel instead of aluminium, the detection of disbond and delamination together by radiography, drycoupling and PET is impossible because the difference in density between the composite and maraging steel is about five times. This causes the setting of parameters in radiography and acoustic impedance mismatch in ultrasonics makes difficult. In this case neutron radiography may offer a solution as the higher density has hardly any attenuation to it because neutrons interact with nuclei. That is why the different NDT techniques are complementary, as no single technique offers complete solution to all the problems.