Higher Order Mode Cluster ( HOMC) Guided Waves - A novel technique for accurate detection and quantification of hidden corrosion

Abstract

Corrosion happening at the support regions, under sleeves, in interfaces of the pipes are severe and need reliable assessment. These hidden corrosion vary in nature based on the type of hidden region such as in resting supports, welded sacrificial pads or clamp supports just pipes wrapped in protective wrapping. Ultrasonic NDT plays a major role in the inspection of these supports. Several NDE Techniques exist for such inspection but quantifying the wall loss in an accurate manner depends on the nature and extent of 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 verified at several field sites. Ultrasonic guided waves (circumferential or axial modes), once generated will be reflected or transmitted from corrosion and other features on the pipe. Inspection can be carried out from the accessible portion of the pipe . This could be done as an in-service inspection without emptying the pipe. HOMC guided waves are unaffected by the point of incidence of the probe. Accurate Wall loss estimation is possible together with cross sectional profile of maximum thickness loss. Using this information an accurate remaining wall thickness assessment is achieved. The technique has been deployed from pipes 2inches and above and upto 20mm wall thickness.