Pipelines have various critical regions where the susceptibility of corrosion is very high and the possibility of inspecting them is very low.
These Critical Regions include:
Conventional NDT techniques do not help in reliable inspection of these regions and very often excavation of buried pipes, coating removal, clamp removal followed by visual inspection has been the standard practice employed by most owners. Techniques that provide some information do not have the sensitivity to find small defects such as localized pitting corrosion.
A new concept for the improved inspection of corrosion at the support region of pipelines using a short-range ultrasonic guided wave technique that uses a collection of Higher Order Modes Clusters, called here as HOMC has been developed and patented by Dhvani.
Ultrasonic guided waves (axial modes), once generated will be reflected from corrosion and other features (welds, etc.) on the pipe. Inspection can be carried out all around the pipe by moving the probe around the pipe circumference. Inspection can be carried out with the scanner at distances up to 2 m, along the length of the pipe, from the region of interest.
Experimental data obtained from the calibration sample with programmed defects and on field tests show that the size and location of the defects correlates well with the time-of flight and amplitude ratio of the reflected signals from the defects. A and B-scan images were used to visualise and quantify the defect size and location.
The technique is capable of detecting small pin hole type defects, such as caused by pitting corrosion, as well as large area corrosion damage. Other types of defects such as cracks, weld defects, gouging damage, etc. are also imaged using the method. The presence of surface coatings such as insulation does not affect the wave.
A Semi-Automated Scanning system called CRISP(Critical Region Inspection Scanner for Pipes ) has been developed and tested to ensure high speeds of inspection in line with industry requirements.