GB2109113A

GB2109113A - Method and means for inspecting a tube for the presence of magnetic spots in the material thereof

Info

Publication number: GB2109113A
Application number: GB08133991A
Authority: GB
Inventors: Christianus Johannes Mar Wolff
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1981-11-11
Filing date: 1981-11-11
Publication date: 1983-05-25

Abstract

To detect the presence of magnetic spots in the wall of a metal tube 4 (such as a drill collar), this tube is displaced in the direction of its longitudinal axis, and variations in magnetic flux are measured inside this tube by sensor 11 at a fixed location with respect to the earth. <IMAGE>

Description

SPECIFICATION Method and means for inspecting a tube on the presence of magnetic spots in the ma terial thereof The invention relates to a method and means for inspecting a tube, such as a drill collar used in rotary drilling equipment, on the presence of magnetic spots in the material thereof.

Drill collars are used in rotary drilling operations for drilling boreholes or wells in underground formations. In such operations a plurality of drill collar sections are screwed together in end-to-end relationship. The tubular string thus obtained is supported at one end thereof to the lower end of a drill string, which consists of a plurality of drill pipe sections that are screwed together in end-toend relationship. The upper end of the drill string is supported in a known manner from a drilling rig located at the surface of the earth.

The drill pipe string supporting the drill collar section is positioned in a hole or well that is being drilled in the earth, and the lower end of the drill collar section carries a drilling bit and optionally a downhole motor.

The drill collar sections have a greater wall thickness and a greater diameter than the drill pipe sections, and the lowermost sections of the drill collar string consist of non-magnetic material, such as monel metal, to allow in the interior of these sections the application of measuring equipment that is designed to measure magnetic properties in the formation layers in which the borehole or well penetrates.

It will be appreciated that for obtaining reliable measurements with such down-hole measuring equipment, the drill collar sections wherein the equipment is located, as well as the sections adjoining these sections should be absolutely non-magnetic, or in other words should have an extremely low magnetic permeability.

Suitable methods are available for manufacturing non-magnetic tubular material. Since such methods are known per se, they do not need any detailed description thereof.

Prior to applying the non-magnetic drill collars in a drilling operation, they should be inspected on the presence of magnetic spots in the material of the pipe. Such areas where the pipe material is magnetic by some default in the manufacturing process, are also indicated as "hot spots".

Up till now, the inspection procedure to detect the presence of hot spots in nonmagnetic drill collars and other non-magnetic tubular material was carried out by measuring the magnetic permeability of the drill collar (or tubular material) at various places distributed over the area of the outer wall of the drill collar. The measuring equipment suitable for this purpose included a magnetic source and a magnetic flux meter. For inspection of the tube, the measuring equipment was displaced from one spot on the pipe to another, and as areas of the pipe were faced that could not be magnetized, no magnetic flux was measured by the flux meter. However, when facing a spot where the material did not have the required non-magnetic property, the material was magnetized to an extent that could be detected by the flux meter.

As has been observed above, it is of utmost importance in drilling operations that drill collars adapted for housing measuring equipment, such as a compass or a logging tool for measuring magnetic properties of the strata that are being passed by the hole that is being drilled, should be absolutely free from the socalled hot spots, since the magnetic properties of such spots interfere with the measurements taken by such equipment. This leads to incorrect measurements, and consequently to faulty decisions by the drilling crew.

Although the inspection method based on the measurement of magnetic permeability of the material of the drill collars was considered to be reliable for checking the suitability of non-magnetic drill collars, Applicant has now found that occasionally problems are met in the field with drill collars that had passed the inspection. Such collars, although showing a very low magnetic permeability during the inspection prior to, and after its use in a borehole drilling operation, nevertheless influenced any measuring operations carried out in the borehole at the level of the drill collars, if such measurement operations were aimed at measuring or detecting magnetic flux in a borehole, such as when obtaining data of the magnetic properties of the surrounding formation strata, or when obtaining information on the direction of the earth-magnetic field.

Object of the invention is a method and means of inspecting a tube on the presence of magnetic spots in the material of the tube, which method and means do not show the above-described drawback.

The method according to the invention, for inspecting a tube with a substantially straight longitudinal axis on the presence of magnetic spots in the material of the tube, includes the steps of displacing the tube in the direction of its longitudinal axis and solely measuring inside the tube at a fixed location with respect to the earth any variation in magnetic flux that results from magnetic spots in the material of the tube.

The means according to the invention for inspecting a tube with a substantially straight longitudinal axis on the presence of magnetic spots in the material of the tube, includes a first support, measuring equipment for detecting variations in magnetic flux, and a second support, the first support being adapted for supporting the tube and allowing displacement thereof in the direction of its longitudi nal axis, the measuring equipment consisting of a sensor for measuring variations in magnetic flux and of means for storing and/or disr,iaying measured data, and the second support being adapted for supporting the sen s-Jr at a location of the longitudinal axis of the tube and immovably with respect to the longi radial direction of the axis.

It will be appreciated that the measuring equipment used in the present method and apparatus, does not include a magnetic source iS is applied in the prior art technique wherein the magnetic permeability of the material of the tube is determined in order to trace hot spots in the material of the tube.

An extremely accurate detection of the mag rietic spots is reached by the use of the method according to the invention, wherein the variation of the magnetic flux at a fixed point is measured when the tube that is to be tested is passed along said fixed point. By the present technique even hot spots having the size of a pin point can be traced. Those spots of the material of the tube that are not nonmagnetic as result of a faulty manufacturing method, will become magnetic under influence of the earth magnetism, and the magnetic flux of these spots is measured by the present technique by comparing the magnetic flux at the immobile measuring point with the magnetic flux in said point when the tube is passed over said point.

in view of the often extremely low degree of magnetization of the hot spots of a tube, inspection methods that are designed to directly measure the magnetic flux of hot spots by displacing the sensor over the surface of the pipe, should be carried out at sites where magnetic or electro-magnetic sources are not present outside the tube to be inspected.

Such sites are to be found outside towns and industrialized areas, and at a sufficient distance from electric conduits such as hightension wires, railroad tracks for electric trains, pumping stations, subsurface pipelines with corrosion control equipment, etc. The tubes to be inspected at such sites should be supported on a wooden support in order to eliminate the presence of any outside magnetic source that would jeopardize the delicate measurement of the magnetic flux. A drawback of this manner of inspection is that such sites are nearly always located at remote places, which renders such inspection expensive. This problem, however, can now be avoided by the use of the method and means according to the invention, wherein the sensor that measures the magnetic flux is kept immobile with respect to the earth, and the tube to be inspected is displaced with respect to the sensor.

The inspection means according to the invention compares the magnetic flux pattern inside the tube with the flux that is normal at the location of the sensor when the tube is not present, and the differences existing between the measured magnetic flux pattern and the normal magnetic flux at the measuring point thus all originate from the hot spots in the material of the tube that is displaced relative to the sensor, when these spots are passed along the sensor during the inspection.

As the changes in magnetic flux thus indicate the hot spots, no special precautions have to be taken at the site where the inspection takes place, other than maintaining all electric equipment in a steady state, and keeping all magnetic sources (except the hot spots in the tube) immobile.

By inspecting the tube at the inside thereof by the sensor, all magnetic spots, even those that are so small that they are not detectable at the outside surface of the tube, will be detected. This is of importance, since the measuring techniques carried out in a well and based on the detection of the magnetic properties of subsurface strata or of the direction of the earth magnetism, all take place at the inside of the tube when present in a borehole or well.

The invention will now be described by way of example in more detail with reference to the drawing which shows schematically a side view of the inspection means according to the invention.

The inspection means shown in the drawing consists of a first support 1 including a framework 2 provided with rollers 3 for supporting a tube 4 with a substantially straight longitudinal axis 5, which tube is to be inspected on the presence of magnetic spots in the material thereof. The rollers 3 are arranged to allow displacement (see arrow 6) of the tube 4 in the direction of its longitudinal axis 5.

The means according to the invention further comprise a second support 7, said support including a housing 8 mounted immovably on the floor 9 of a workshop (or any other suitable place for carrying out the inspection) and an arm 10 extending along and at some distance above the framework 2 of the first support 1. The arm 10 can be adjusted vertically such that irrespective of the diameter of the tube 4 to be inspected, the central axes of the arm 10 and the tube 4 can be made to coincide. The arm 10 carries a sensor 11 at one of its ends. The sensor is adapted for measuring variations in magnetic flux. The measured data are transmitted via electric leads (not shown) through the arm 10 tp means for storing the data. These means (not shown) are located within the housing 8 and are known per se. Display means 1 2 are provided to show the presence of detected magnetic spots in the material of the tube 4, when the latter is passed over the sensor 11 by being displaced along the axis 5 (see arrow 6).

In carrying out the method according to the invention, the tube 4 that is to be inspected is placed on the rollers 3 in the position shown in the drawing. Prior to starting the inspection, the measuring equipment consisting of the sensor 11, the data storage means (not shown), and the display 1 2 is activated. If there are any magnetic sources present within measuring distance of the sensor 11, measures should be taken to obviate these sources from generating a magnetic flux that varies in magnitude. Such sources should then be deactivated in a sense such that the sensor 11 does not detect any variation in magnetic flux with time. Such deactivation includes immobilization of displaceable magnetic sources, or adjusting the sources such that a steady state situation exists.

When the sensor 11 does not detect any variation of the magnetic flux, the inspection of the tube 4 can take place. Thereto, the tube 4 is displaced in the direction (see arrow 6) of its longitudinal axis 5, thereby passing over the sensor 11. Any area or spot of the material of the tube 4 that is magnetized, will then be detected by the sensor 11 that spots a change in magnetic flux. The location of such an area or spot, as well as the magnitude of the degree of magnetization can thus be determined. The measuring results can be read directly from the display 12, but also be retrieved in a later stage from the data storage means (not shown) that is housed within the housing 8.

It will be appreciated that since the sensor 11 is not displaced during the inspection of the tube 4, the magnetic flux detected by the sensor and originating from other sources than the pipe (such as from electric conduits, or from magnetic parts of the supporting structures 1 and 7, or from any other metallic structures present in the workshop where the inspection means is situated) will not change.

Any variation in magnetic flux that is detected by the sensor 11 when the tube 4 is displaced relatively to the sensor, thus originates from the presence of magnetic parts in the material of the tube 4, when these parts pass along the sensor 11. These parts can be marked directly during the inspection period, or be traced afterwards at the hand of the records taken.

As has been observed hereinabove, the support that carries the sensor 11 is mounted so as to be immovable with respect to any of the outside magnetic or electro-magnetic sources that may be present in the neighbourhood of the inspection means. To this end, the support 7 is connected to the framework 4 of the support 2, and both supports are placed immovably on the floor 9. However, the support 7 or part thereof may be arranged to be displaceable with respect to the support 11 during periods that no inspection takes place.

In this manner, the sensor 11 and the arm 10 can be moved out of the way if such should be necessary to allow an easy access for the operators when handling the tube 4 for placing it on the rollers 3, or removing it therefrom. In an alternative manner, the two supports 2 and 7 may be mounted separately on the floor 9 of the workshop.

It will be appreciated that the rollers 3 may be replaced by carriages (not shown) provided with wheels that are suitable to cooperate with track-shaped parts of the framework. The carriages as well as the wheels should then be made of non-magnetic material, since otherwise when being displaced along the tracks they will be the cause of inaccurate readings of the sensor.

It will be understood that, although the sensor 11 in the drawing is shown to be arranged coaxial to the central axis 5 of the tube 4, the invention is not limited to this arrangement. Good results will also be obtained when the sensor 11 is slightly offcentre with respect to the axis 5.

The arm 10 may be supported by rollers (not shown) arranged so as to cooperate with the interior wall of the tube. Excessive bending of the arm can then be prevented when inspecting long tubes. In an alternative manner, the arm may extend beyond the sensor, and be supported at a location at the free end of the framework 2. Placing the tube on the rollers 3 is then somewhat complicated, and therefore the use of the above-mentioned rollers for supporting the arm 10 will often be preferred.

When tubes of widely varying diameters are to be inspected on one and the same inspection apparatus, the arm 10 may be made adjustable in a vertical sense, such that the distance between the central axis of the sensor and the framework of the first support is variable. By adjusting this distance, the sensor can be placed such that the central axis of the sensor and of the tube substantially coincide.

Various types of sensors may be used in the inspection means according to the invention.

In one embodiment of the invention, the sensor may include a flux gate having the central axis thereof coinciding with the longitudinal axis of the tube that is to be inspected.

Hereby, the component of the magnetic flux in the direction of the longitudinal axis is measured and the variations in this component indicate the presence of hot spots in the material of the tube.

In another embodiment of the invention, two flux gates facing each other are included in the sensor. The central axes of the gates coincide with the longitudinal axis of the tube that is to be inspected. Hereby tiie gradient of the axial field component of the magnetic flux of the hot spots of the pipe is detected.

In still another embodiment, the sensor may include three flux gates that are mutually perpendicular, and measure separately three components of the magnetic flux of the hot spots that are displaced along the sensor when the tube that is to be inspected is moving over the sensor.

Claims

1. Method for inspecting a tube with a substantially straight longitudinal axis on the presence of magnetic spots in the material of the tube, the method including the steps of displacing the tube in the direction of its longitudinal axis and solely measuring inside the tube at a fixed location with respect to the earth any variation in magnetic flux that results from magnetic spots in the material of the tube.

2. The method of claim 1, wherein the component of the magnetic flux in the direction of the longitudinal axis is measured.

3. The method of claim 2, wherein the component is measured in two opposite directions of the longitudinal axis.

4. The method of claim 1, wherein three perpendicular components of the magnetic flux are separately measured.

5. The method of inspecting a tube on the presence of magnetic spots present in the material of the tube, substantially as described in the specification with reference to the drawing.

6. Means for inspecting a tube with a substantially straight longitudinal axis on the presence of magnetic spots in the material of the tube, the means including a first support, measuring equipment for detection variations in magnetic flux, and a second support, the first support being adapted for supporting the tube and allowing displacement thereof in the direction of its longitudinal axis, the measuring equipment consisting of a sensor for measuring variations in magnetic flux and of means for storing and/or displaying the measured data, and the second support being adapted for supporting the sensor at a location of the longitudinal axis of the tube and immovably with respect to the longitudinal direction of the axis.

7. The means of claim 6, wherein the first support includes a framework and transport rollers mounted thereon for supporting and displacing the pipe.

8. The means of claim 6, wherein the first support includes a framework and carrier means for carrying and displacing the pipe with respect to the framework, the carrier means being made of non-magnetic material and being provided with wheels running along track-shaped parts of the framework.

9. The means of claim 7 or 8, wherein the framework and the second support are interconnected to prevent displacement of the sec ond support with respect to the framework during the inspection of the pipe.

1 0. The means of any one of the claims 6-9, wherein the second support includes an arm for supporting the sensor, said arm extending in the longitudinal direction of the first support and being adjustable to vary the distance between the sensor and the first support.

11. The means of any one of the claims 6-10, wherein the sensor includes a flux gall.

with the central axis thereof coinciding with the longitudinal axis.

1 2. The means of any one of the claims 6-10, wherein the sensor includes three flux gates that are mutually perpendicular.

1 3. The means of any one of the claims 6-10, wherein the sensor includes two flux gates facing each other and having the central axes thereof coinciding with the longitudinal axis.

1 4. Means for inspecting a tube on the presence of magnetic spots in the material of the tube, substantially as described in the specification with reference to the drawing.