Composite Repairs Integrity Assessment: An Overview of Inspection Techniques
Authors: Mohd Ramli Siti Haslina , Ariffin Rosman , Chik Ir Hambali 
Published: November 2020

Abstract

Objectives/Scope
Composite repairs have been increasingly applied for repairs of piping and pipelines in the oil and gas industry, and thus there is a growing need to monitor their in-service integrity and to better manage any loss of containment of the product. There are many challenges of inspecting composite repairs including accessibility, inhomogeneous and anisotropic structure, probability of detection, lack of adequate standards and unfamiliarity with composite materials amongst others. PETRONAS has then performed a series of evaluation to assess potential NDT techniques for integrity assessment of composite repairs. This paper provides an overview of the inspection techniques that have been evaluated on composite repairs, and a summary of the findings of the evaluation.

Methods, Procedures, Process
The current practice for inspection and monitoring of composites repair in oil and gas pipings and pipelines are usually conducted based on ISO 24817 whereby visual inspection is generally performed to observe any irregularities on the surface like discolouration, cracks, chalking and blistering. This will usually be followed through with a coin tap test and hardness testing. Upon any findings of anomalies, further investigation is then performed to determine the integrity of the wrap, depending on the type and severity of defects. The methods mentioned above serve as initial inspection tools to provide an indication of the condition of the repair. Any findings observed during there inspections would render application of other non-destrcutive testing technqiues aimed to inspect both the substrate and composite repair system, and to demonstrate the overall integrity of the repair system. ISO 24817 have stated the general techniques that can be used to inspect the composite overwrap repairs including Ultrasound technique, Radiography, Acoustic emission etceteras. PETRONAS has performed a series of assessments on various inspection technqiues to seek for suitable inspection methods for the composite overwrap system, composite/substrate interface and/or substrate. A total of ten (10) had been evaluated thus far, and amongst the techniques include Laser Shearography, X-Ray, Microwave technique, Dynamic Response Spectroscopy (DRS), Acoustic Emission (AE), Computed Radiography (CRT), Pulse Eddy Current and Metal Magnetic Memory (MMM).

Results, Observations, Conclusions
The evaluation observed that some technqiues have shonw the ability to inspect the composite repairs, whilst some can only be used for screening. A few techniques have been observed to have additional advantages and are readily deployable.

Novel/Additive Information
This paper provides an overview of the effectiveness as well as the pros and cons of several NDT techniques that have been evaluated on composite repairs for piping, pipeline and vessels. This paper also provides a quick reference on the acceptance criteria and selection of suitable inspection method of assessing the integrity of composite repairs for the oil and gas industry.