Electricity: measuring and testing – Magnetic – Magnetic sensor within material
Patent
1998-01-08
2000-03-14
Snow, Walter E.
Electricity: measuring and testing
Magnetic
Magnetic sensor within material
324240, G01N 2782, G01R 3312
Patent
active
060377674
DESCRIPTION:
BRIEF SUMMARY
The present invention relates in a general way to the magnetic inspection of objects or products which form or include a wall comprising at least one layer of magnetic material, in particular steel, for the purpose of detecting faults, such as cracks, in such products.
This type of inspection falls into the category of non-destructive inspection, for which there are already known inspection techniques involving the measurement of the leakage flux or the dispersion flux, and so-called eddy-current inspection techniques, which are used in particular for detecting faults in ferrous products.
The present invention is aimed particularly at the inspection of long, elongate products, the layer to be inspected of which is not directly accessible to the inspection equipment, or the faults to be detected of which lie within the thickness of the wall of the product, at a relatively large distance from that surface of this wall which is accessible to the inspection equipment. Such products may have a solid general cross-section, such as cables, in particular those coated with one or more protective or reinforcing sheaths, the inspection of which is carried out from the outside, or they may have a hollow cross-section, such as tubes, pipes, flexible pipes etc., the inspection of which may be carried out from the outside or from the inside. It is pointed out that the term "long products" should be understood to mean any elongate product whose length is such that it is practically impossible to access both of its ends simultaneously in order to completely magnetize the product without moving the magnetizing means, or that the power necessary for carrying out such a complete magnetization would be too great to be realized on an industrial scale.
The present invention is aimed in particular at the inspection of rigid or non-rigid tubular products for which the inspection must be carried out from the inside of the product. Such an inspection carried out from the inside proves to be necessary in particular for substantially rigid or flexible conduits, such as the pipes or pipelines used in the offshore oil production industry. This is because the in situ inspection of such conduits from the outside is often made almost impossible because of their environment. For example, the semi-rigid pipes or the flexible pipes used for transporting oil from a wellhead lying on the sea bed up to a surface drilling platform are usually equipped with connection means at their ends and with intermediate support means, such as floats, which prevent any accessibility from the outside. Now, it is precisely these connection or support regions which are subjected to the greatest stresses, and therefore exposed to the greatest risk of the appearance of cracks, crazes or fractures. Moreover, it is in these highly-stressed regions that other faults, such as pinholes or corrosion, may involve the greatest risks of cracking and of reduction in the mechanical strength of the pipes. However, these pipes conventionally include at least one internal sealing layer or an internal protective coating which means that the magnetic layer to be inspected is not directly accessible.
Although the invention is of general application to any product having at least one layer of ferromagnetic material, it is of particular advantage for products whose structure prevents or complicates the implementation of conventional inspection methods. Its aim is particularly to allow the inspection of the rigid, semi-rigid or flexible pipes used in the oil industry, which will be taken hereafter as a typical example of the application of the procedure and of the device according to the invention.
The rigid or semi-rigid pipes used for transporting oil generally consist of a steel tube which has a relatively large wall thickness and is often internally coated with a layer of a polymeric synthetic material, for example polyethylene, several millimetres in thickness. Furthermore, there is a tendency to use steel pipes of increasing thickness, this possibly being as much as or exceedin
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patent: 4867205 (1989-09-01), Bournazel et al.
patent: 5336998 (1994-08-01), Watts et al.
patent: 5359939 (1994-11-01), Watt
Crescenzo Eric
Lembeye Philippe
Coflexip
Snow Walter E.
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