According to statistics compiled by the U.S. Office of Pipeline Safety, external mechanical
damage is one of the primary failure mechanisms for transmission pipelines. Mechanical damage can
be described as a pipeline deformation with or without secondary features such as gouging or cracking.
These types of features are a major concern of pipeline integrity engineers. This is why inline
inspection tools specifically designed to detect geometry deformation have been used in the industry
for many years. A pipeline dent of sufficient depth can reduce the burst pressure of the pipeline. Some
of the most severe pipeline conditions possible occur when a dent is in coincidence with another defect
such as a gouge or a crack.
Since the development of Tri-axial Magnetic Flux Leakage (MFL) inspection tools, a number
of pipelines have been inspected with both caliper and MFL inspection tools. A large database of
features was created that contained detailed information from both the caliper inspection tool as well as
signal information from the MFL tool for dent like features. An empirical study of the relationship
between the MFL signal of a dent and the recorded mechanical deflection of a dent from a calliper tool
was conducted and the results from this study indicated it is possible to accurately predict the size
(Depth, Length, and Width) of a dent from tri-axial MFL inspection tool data. The methodology of
sizing dents and the accuracy of dent size predictions will be demonstrated in this paper.