L52333 NDE and Inspection Techniques Applied to Composite Wrap Repairs

Abstract

The objective includes: Assess commercially available inspection methods to validate integrity of composite repair systems. Identify applicability to inspect composite overwrap and parent metal for both onshore and sub-sea pipelines (where information is available). Identify sources of data to include other users of composite materials(aerospace/aircraft, naval/ship repairs). Identify procedures and technologies to assess inspection effectiveness and provide a gap analysis. Interface with other PRCI projects on long-term testing of composite repairs and other joint industry projects on composite repairs to improve our understanding of long term durability of repairs. Identify global experience with composite repairs; not just North America. For general wall loss, radiography or electromagnetic techniques appear to be the best candidates. Standard radiography techniques can detect changes in wall thickness over a large area. Saturated low frequency systems, e.g. SLOFEC are good for a quick rapid scan of the area of interest. Pulsed eddy current, e.g. PEC, is also available for a general survey of the underlying substrate. For pinhole leaks, the electromagnetic techniques do not have sufficient resolution to detect defects of order 20 mm (0.8 in.) diameter and less. Standard radiography techniques can detect pinhole leaks down to diameters of 3 mm (0.12 in.) or less. Tangential radiography techniques are generally good for defect sizing but there are practical limitations with chord length (i.e. beam path through the pipe wall). Ultrasonic techniques could offer a potential solution but is currently limited due to the high attenuation of the composite repair material where through the repair inspection could only detect large diameter defects greater than 25 mm (1 in.) diameter on thin repairs less than 5 mm (0.2 in.). Detecting pin hole defects by applying the ultrasound along the axial direction of the substrate, effectively skipping the ultrasound under the repair, showed more promise. For delamination or debonding of the interface between the composite laminate and the steel substrate, laser shearography and microwave inspection appear to offer the best solution. Currently there is no single inspection technique that can be applied with confidence to the inspection of interfacial delaminations. Further developments are on-going to provide a solution to this challenging inspection problem. Acoustic emission is able to give an overall picture of the damage within the composite under live loads. It can be used as a QA tool to test the integrity of the repair. However, it is difficult to interpret the signals to gain any quantitative information about a particular defect.