United States Department of Transportation
i
Physically-Based Model for Predicting the Susceptibility of Asphalt Pavements to Moisture-Induced Damage
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2010-09-01
[PDF-5.51 MB]
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Abstract:The proposed work is to develop a phase sensitive technology that could detect coating disbondment on steel pipe from above ground, thus locating potential corrosion failure points. The system would consist of two components, a stationary signal generator that is attached to a test point and a detector that is carried along the pipeline. Sinusoidal or pulse excitation signals may be used. A wireless link between the generator and the detector provides accurate synchronization. An abrupt change of signal phase is expected at the disbondment. There is currently no method to detect or locate a disbonded coating from above ground. Existing pipeline potential gradient surveys, both DC and AC voltage, make use of only amplitude data. While amplitude methods can detect an active holiday (break) in the coating, a disbonded coating can shield active corrosion from both detection and cathodic protection. Stated another way, the space between a disbonded coating and the pipe can house an active corrosion cell. Until there is an actual holiday in the coating, the corrosion cell cannot be detected with current technology. A holiday will allow increased cathodic protection current to flow to the pipe in the immediate vicinity of the holiday, but may not reach the extremities of a large disbondment. A disbonded coating can contain an active corrosion cell that is undetectable until serious damage has occurred to the pipe wall. There is no exterior method that can reliably detect disbonded coating at this time. The coating effectively "shields" areas of active corrosion within the disbondment from DC or AC voltage gradient surveys. Internal methods, such as magnetic flux leakage (MFL) pigging may detect wall thinning but will not differentiate causes. MFL pigging is expensive and may not be possible on lines with bends or diameter changes. The proposed work is to provide a completely new method for surveying pipelines. The object of the proposed work is to develop a technology that could detect coating disbondment on steel pipe from above ground, thus identifying potential corrosion locations before the pipeline fails. The deliverable would be prototypes of two components, a stationary signal generator and a hand carried detector. The signal generator would be attached to the pipeline at a test station. The hand-held device would be carried along the pipeline to acquire signal phase and amplitude measurements from the pipeline.
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