Corrosion detected by in-line inspection tools or bell-hole examination must undergo subsequent evaluation to determine the proper action, if any, to be taken. A corrosion assessment must be made before deciding to repair the corroded area or to remove it from service. Traditional practice uses manual measurements along a mapped grid over the locations on the pipe. Newer, more accurate corrosion assessment methods use detailed measurements of the corrosion profile rather than simply the length and maximum depth of the defect area. The industry needs a simple, more accurate method for measuring corrosion patches in the field under adverse environmental conditions. Measurements must be accurate enough to support advanced assessment methods. The design should lend itself to mass production and be inexpensive enough that an operating district or a maintenance department can have a measuring system available for use by field personnel. Further, it should be easy to make the measured data available to engineering personnel for detailed analysis.

A flexible printed circuit board laid on the outside circumference of the pipe will provide a reference point to which defect depth can be referenced. The printed circuit card material is imprinted with lift-off transducers on a high-resolution grid, and these transducers are scanned, and the data recorded, then an accurate image of the defect can be obtained. A laptop computer is used to power the array and record the acquired data. Software will display the defect image and automatically extract necessary information for defect assessment. Larger defect areas will be assessed using multiple scans. Software will merge multiple scans into a seamless image.

This paper presents a new device for measuring, documenting and assessing external corrosion on steel pipelines. Feasibility and design of the new system were funded by the U.S. Department of Energy through the National Energy Technology Laboratory. National Energy Technology Laboratory.

An effective method of measuring and mapping external corrosion on steel pipelines has been developed. Several enhancements, durability improvements and field “hardening” have augmented the serviceability of the method and device since the initial feasibility studies and early prototypes were reported.1,2 Software produces a color contour map of the corrosion, which identifies the depth and location of the deepest pit, the axial length of the corrosion, and utilizes the industries widely accepted critical engineering assessment methods to calculate a safe operating pressure.


Pipeline operators use both external and internal surveys to evaluate the condition of their pipelines. In-line inspection (ILI) tools are a common method to evaluate pipelines and pinpoint damage. ILI surveys can provide information on welds, branch connections, valves, wall thickness changes caused by corrosion, and other imperfections in the pipe.

Once features are identified, bell-hole excavations verify the quality of reported features. While verification serves many purposes, the primary one is to accurately quantify the extent of the features so that defect assessment and repair can be completed to ensure pipeline integrity is maintained cost effectively. Secondary benefits include the recording of feature information for use on subsequent inspections.

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