Measuring and testing – Inspecting
Reexamination Certificate
1999-09-29
2001-01-09
Raevis, Robert (Department: 2856)
Measuring and testing
Inspecting
Reexamination Certificate
active
06170344
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to pipeline distortion monitoring. For either above-ground, under-ground, or submarine pipelines there is a possibility that, over time, geometric distortions may occur due to local earth heave or subsidence. If the pipeline distortion at some point becomes too large, there is the possibility of pipeline rupture with possible undesirable human safety, economic, and environmental consequences. To avoid the possibility of such undesirable consequences, a regular survey of the pipeline dedicated to assessing its geometric stability is highly desirable.
Distortion monitoring of pipelines is essential to forecasting integrity changes which allow corrective measures to be taken before actual pipeline failure occurs. Pipeline distortion monitoring has the unique objective of assessing the geometric stability of a pipeline and represents a totally different function than pipeline inspection which has as its objective the monitoring of the inner surface of a pipeline for corrosion and weld integrity. Pipeline distortion monitoring has a unique additional element distinguishing it from pipeline inspection. This is the element of time over which the pipeline shifts from one time epoch to another. Pipeline distortion monitoring requires a comparison of the present pipeline geometry to that which existed at an earlier epoch, and a determination of both the angular and linear shifts that have occurred in the pipeline at all points along its length.
A pipeline PIG is a mechanism that travels through a pipeline detecting profile, ovality, displacement of oil as well as sensing other features of the pipeline. Various prior art pipeline PIGs have relied on special hardware elements to measure distortion characteristics. Two concepts for pipeline distortion monitoring have used a strapdown attitude reference system to measure the attitude of a PIG relative to a local vertical frame of reference as the PIG traverses the pipeline, together with a secondary means which allows the attitude of the PIG relative to the pipeline to be determined. One such concept, described by Levine (U.S. Pat. No. 4,524,526), utilizes a mechanical arm which makes physical contact with the pipeline, and whose angular position with respect to the PIG body provides a measurement of the PIG attitude relative to the pipeline. A second concept, described by Adams et. al. (U.S. Pat. No. 4,945,775), utilizes sonar measurements to provide the PIG attitude relative to the pipeline. By either means, the PIG attitude relative to the local vertical frame, together with the PIG attitude with respect to the pipeline provided by the secondary means, allows the pipeline attitude relative to a local-vertical geographic frame to be determined at all points along the course of the pipeline. Comparisons with the same information at an earlier epoch then allows an assessment of pipeline distortion to be made.
Another concept applicable to pipeline distortion monitoring, described by Lara (U.S. Pat. No. 4,799,391), utilizes a set of angular rate measurements from a triad of three orthogonal gyros, and a set of linear acceleration measurements from a triad of orthogonal accelerometers to derive the curvature parameters of the pipeline along its entire course. Then, comparison of these curvature parameters with the same parameters at an earlier epoch provides an indication of pipeline geometric stability.
SUMMARY OF THE INVENTION
A strapdown inertial system is used on a pig to provide three dimensional attitude and velocity of the pig as it travels through a pipeline. The system includes an IMU and odometer to collect attitude and linear displacement data. The body to local vertical attitude of the pig is corrected for two effects to allow it to provide the desired pipeline attitude relative to the local vertical frame. The first correction is for the fixed angular offset between the IMU and the pig body while the second correction is for the maneuver induced angular offset of the pig relative to the pipeline that occurs during pipeline bends. The velocity vector of the pig is corrected for the known lever arm between the pig center of gravity and the IMU location which causes the pig velocity to be affected during angular motions of the pig. Once both the attitude and velocity vector of the pig have been corrected, they may be blended using a complementary filtering approach to yield the pipeline attitude relative to the local vertical frame. The pipeline distortion monitoring function is implemented using the derived geometric parameters of the present survey and the comparable quantities derived from a prior survey.
REFERENCES:
patent: 4524426 (1985-06-01), Levine
patent: 4799391 (1989-01-01), Lara
patent: 4945775 (1990-08-01), Adams et al.
patent: 6002974 (1999-12-01), Schiffmann
Fredrick Kris T.
Honeywell Inc.
Raevis Robert
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