Application of Remote-Field Eddy Current Testing to Inspection of Unpiggable Pipelines

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• In-Line Inspection/Pigging
• Emerging Technology
• Remote Sensing
• Internal Corrosion
• External Corrosion

Main Objective

The project will conduct a technology assessment to determine the requirements for a new remote-field eddy current (RFEC) testing system.

Public Abstract

The project will conduct a technology assessment to determine the requirements for a new remote-field eddy current (RFEC) testing system. The purpose of the research is to determine if an ILI using RFEC testing is adequate to inspect currently unpiggable pipelines. The tool developed under this research is expected to be able to detect corrosion and mechanical damage. The researchers will design, fabricate and test a breadboard RFEC system using two excitation coil configurations (one smaller, one collapsible).

Status History

Project initiated in October 2002; 12 month project duration.

Status: 6/13/03

Many pipelines contain internal restrictions that do not allow the passage of inspection pigs that use con�ventional inspection technology. The purpose of this project is to investigate the feasibil�ity of a remote-field eddy current (RFEC) inspection method that utilizes either a unique collap�sible excitation coil or a small rigid excitation coil that can pass through internal pipeline restrictions.

Task 1, Technology Assessment, has been completed. The purpose of this technology assessment was to (1) iden�tify recent developments in RFEC testing that could be relevant to the project, and (2) determine inspection requirements for unpiggable pipelines (e.g., size constraints) that would guide deter�mination of parameters for the RFEC system. The RFEC references most useful to the project dealt with (1) shielding that allowed the exciter-to-receiver spacing to be reduced, (2) effects of coil tilt, (3) improvement in scanning speed using local magnetic saturation, (4) coil design improvements, and (5) use of a small excitation coil to allow passage through restricted areas. It was determined that target pipe sizes for development of a collap�sible RFEC system would be in the range of approximately 4 to 22 inches in diameter. Target obstacles to be addressed are reduced port valves (primarily plug valves) and bends with radii smaller than 1.5 inches in diameter. Nonconventional, self-powered, pigging devices (currently under develop�ment) are potential plat�forms for an RFEC system.

Task 2, RFEC Coil Design, is underway. This task involves the modeling and design of RFEC coils to accommodate the size constraints imposed by internal restrictions. A concept for a collapsible excitation coil was developed. This coil consists of six hinged segments that expand to create a full-diameter coil and then retract to accommodate a smaller diameter restric�tion. Another implementation of the collap�sible coil involves folding the coil into two halves to allow passage through plug valves that have openings that are the same as the pipe diameter in one direction, but are narrow in the other direction.

An RFEC computer model developed previously by Southwest Research Institute is currently being used to evaluate the response from the segmented collapsible coil. The outer perimeter of the coil produces the exci�tation magnetic field; however, the segmented arrangement results in the equivalent of a small-diameter inner coil that produces a field in the opposite direction. This field combines with the main field to reduce the overall field somewhat, but only about 10 percent. This points to the feasibility of using a segmented coil approach.