Measuring and testing – Vibration – By mechanical waves
Patent
1993-05-18
1995-01-31
Noland, Tom
Measuring and testing
Vibration
By mechanical waves
738665, F17D 500, G01M 700, E21B 47022
Patent
active
053850491
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method of inspecting pipelines such as gas pipelines and to a pipeline pig for use in such a method.
Pipeline inspection is important in order to investigate the integrity of pipelines and, if possible, enable warning of possible failure to be given well in advance of such failure so that pre-emptive measures can be taken to avoid it or mitigate its results. A particular problem arises with buried gas pipelines where fracture may have dire consequences.
There have been many proposals for pigs and methods that can monitor the structural condition of a pipeline, including pigs which have optical sensors or cameras, pigs with ultrasonic transducers and the like, but the results achieved with such devices are not always satisfactory, at least partly, because the results achieved may not give any indication of surrounding features in the ground which may lead to fracture in due course. FIG. 12 illustrates a buried gas pipeline P which passes over regions of soft S and hard H soil, where conditions vary greatly from those immediately surrounding them. The passage of heavy vehicles such as that shown at V will eventually cause sagging at region S and hogging at region H as indicated in the two small diagrams to each side of the main figure. Fracture is ultimately likely to occur at points marked *.
GB-A-2146772 proposes using a pig to strike the wall of a pipeline to introduce reverberant vibratory signals into the pipeline and then listening to the resultant reverberations and detecting preselected characteristics of the received sound to indicate unsupported sections or points of load or stress.
SUMMARY OF THE INVENTION
The present invention sets out to provide a way of overcoming problems with the prior art methods used and uses the fact that the structural condition of a pipeline, buried or otherwise, can be indicated by the resistance of the pipeline to translation and torsional movement. Structural conditions that may require to be detected include: changes in pipeline material, wall thickness or cross-sectional shape; type and integrity of joints, tees, branches and other fittings, and, particularly, the method and integrity of support (which includes, for the case of buried pipelines, surrounding ground material).
According to the present invention, a method of monitoring the structural condition of a pipeline and its support includes the steps of:
traversing the interior of a pipeline with a pig;
causing the pig to vibrate in one or more of the vertical, longitudinal, lateral, bending and torsional senses;
transmitting the vibrations into the wall of the pipeline;
measuring the vibration response of the pipeline by detecting one or more of the vertical, longitudinal, lateral, bending and torsional motions of the pig; and
displaying and/or recording the measured data in a form which can be used to identify variations in the structural condition of the pipeline and its support. Bending may be in either the pitching plane (vertical) or the Yawing plane (horizontal) and is used throughout this specification to mean in either plane.
If desired, the vibrational motion of a further trailing pig can also be monitored to provide further data.
The invention also includes a pipeline pig having:
means for causing the pig to vibrate in one or more of the vertical, longitudinal, lateral, bending and torsional senses;
means for transmitting the vibrations into the wall of the pipeline;
means for measuring the vibration response of the pipeline by detecting one or more of the vertical, longitudinal, lateral, bending and torsional motions of the pig; and inspection apparatus also includes
means for displaying and/or recording the measured data in a form which can be used to identify variations in the structural condition of the pipeline.
Preferably, the vibration, which is of low amplitude, is caused by an electromagnetic shaker or by counter-rotating masses and is transmitted at low amplitude through feet to the pipeline wall. The prototype pig is suffic
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patent: 5038614 (1991-08-01), Bseisu et al.
Hunt Hugh E. M.
Kopke Uwe G.
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