Investigating the effect of the methods of creating composite coatings to repair steel pipes based on non-destructive shearography

In this paper, the non-destructive method of shearography is used to identify intentionally introduced defects in composite patches applied to repair fluid-carrying steel pipes. Composite repairs offer a practical and cost-effective alternative for restoring the integrity of fluid-carrying pipelines and their performance depends strongly on the manufacturing method. To evaluate this influence from a non-destructive testing (NDT) perspective, three common fabrication methods, namely hand lay-up with roller, filament winding and vacuum bag injection, are used to produce composite-reinforced steel pipe specimens. Two defect types, fibre-pipe debonding and interlayer delamination, are incorporated in controlled sizes and depths. The specimens are inspected using digital shearography under thermal loading. The results show that vacuum bag injection produces coatings with superior uniformity and allows all defects to be clearly identified. In contrast, the other two methods exhibit manufacturing-related artefacts that hinder defect detection. Overall, the findings demonstrate that the quality of the composite manufacturing process significantly affects the reliability of shearographic inspection for repaired pipes.