GB2242457A - Casing centralisers - Google Patents

Abstract

A device for centralising a casing in a brochure comprises a pair of annular members (10), a plurality of elongate members (11) and means (31) for connecting opposite end portions of the elongate members (11) each to a corresponding one of the annular members (10) so that the annular members (10) are spaced one from another on an axis extending through the annular members (10). The connecting means 31 is a non-welded connection, e.g. nut and bolt, which ensures the non-magnetic characteristics of the centraliser. <IMAGE>

Description

A Device for Centralising a Component in an Enclosure This invention relates to a device for centralising a component in an enclosure and particularly for centralising a casing or pipe in a borehole.

In the building, construction, gas and oil exploration, water, geothermal and waste industries, a casing or pipe is located centrally in a borehole and aggregrate is poured into an annular space between an external surface of the casing or pipe and the circumferential wall of the borehole. In some circumstances the spacing is left void.

Generally, devices are provided for locating a casing or pipe centrally of a borehole. Such devices comprise annular members spaced one from another along an axis extending through the annular members by means of elongate spacers opposite end portions of which are secured to the annular members, the spacers extending circumferentially of the annular members and each spacer being bowed outwardly in a radial direction of the axis so as to engage a circumferential wall of a borehole when located therein. The annular members receive the casing or pipe and each may comprise a pair of arcuate components adapted to be linked one with another so as to be assembled coaxially around an outer surface of a casing or pipe.

In order to reduce corrosion, such devices generally are manufactured in stainless steel such as Austenistic and M.artensitic and other high grade steels. The spacers are welded to the annular members.

A problem associated with welding of Austenistic steels, which are selected because of their non-magnetic characteristics, is that heat generated during the welding process causes molecular changes in the steels resulting in a ferrite buildup. In consequence, when such devices are manufactured of such steels for their non-magnetic characteristics, the devices are not within a material specification that they embody non-magnetic characteristics. Furthermore, the welding process causes discolouration which requires after treatment to clean the surfaces adjacent welds.

According to the present invention, there is provided a device for centralising a component in an enclosure comprising a pair of annular members, a plurality of elongate members and means of connecting opposite end portions of the elongate members each to a corresponding one of the annular members so that the annular members are spaced one from another on an axis extending through the annular members.

Since the invention provides means for connecting opposite end portions of the elongate members to a corresponding one of the annular members there is no necessity to weld the elongate members to the annular members. Therefore, since the elongate members are not welded to the annular members, as with devices known hitherto, a device in accordance with the present invention formed of Austenistic steel will not be outside a material specification that the device embodies non-magnetic characteristics.

Following is a description, by way of example only and with reference to the accompanying drawings, of one method of carrying the invention into effect.

In the drawings: Figure 1 is a plan view of a metal blank prior to formation as a collar of an embodiment of a device in accordance with the present invention, Figure 2 is a plan view of the collar formed from the blank shown in Figure 1, Figure 3 is a cross section on the line III - III of Figure 1 and a diagrammatic representation of a bolt cooperating therewith, Figure 4 is a plan view of a blade of the device, Figure 5 is an elevation of the device, and Figure 6 is a diagrammatic representation showing connection of a collar and a blade of the device.

Referring now to the drawings, an embodiment of a device in accordance with the present invention for centralising a component in an enclosure comprises two pairs of collars 10, and a plurality of elongate blades 11, for connecting the pairs of collars 10 in spaced relation one to another.

Each collar 10 is formed from a rectangular metal blank 12 having webs 13, 14 extending equal distances from opposite sides of the rectangular formation but one of the webs 13 being of smaller dimension than the other web 14 along the said sides. The smaller web 13 is provided with a centrally located square aperture 15 and the larger web 14 is provided with two square apertures 16, 17 of equal dimension one to another and to the aperture 15 of the smaller web 13. The apertures 16, 17 of the larger web 14 are spaced one from another a distance slightly in excess of the dimension of a side of the aperture 15 of the smaller web 13. The blank 12 is provided with two spaced parallel elongate grooves 18, 19 extending adjacent and parallel to corresponding opposite sides of the blank 12 not provided with the webs 13, 14.The blank 12 also is provided with two or more square apertures 20, 21 located on an axis extending parallel to the grooves 18, 1 and extending between the apertures 16, 17 in the larger web 14, the apertures 20, 21 being spaced equidistant from and on opposite sides of an axis extending at right angles to and midway through longitudinal axes of the grooves 18, 19. The blank 12 is pressed so that portions thereof adjacent each of the apertures 20, 21 are recessed, as shown at 23.

The blank 12 is formed into an arcuate collar 10, shown in Figure 2, such that the recesses 23 are recessed from an inner concave surface 24 of the arcuate formation and the webs 13, 14 are curled back upon an outer surface 25 of the arcuate formation to provide complimentary hinge portions 26, 27.

Each of the blades 11, is of elongate rectangular formation each end portion of which is provided with a square aperture 28, 29 each side of which corresponds in dimension with each side of the apertures 20, 21 of the blank 12. As shown in Figure 5 the central longitudinal axis of each of the blades 11 is bowed.

Each of the blades 11, is connected to collars 10 by means of a series of bolts, one of which is shown at 30 and corresponding nuts 31. Each of the bolts 30 comprises a head portion 32 of such dimension as to fill a corresponding one of the recesses 23 and a shank having a threaded portion 33 and an intermediate portion 34 between the head portion 32 and the threaded portion 33. The intermediate portion 34 is of square transverse cross section the area of which corresponds to the area of each of the apertures 20, 21 and 28, 29. Each threaded portion 33, is adapted to receive a corresponding nut 31.

A plurality of collars 10, blades 11, bolts 30, corresponding nuts 31 and hinge pins (not shown) are transported to a site where a borehole has been prepared and devices for centralising casings or pipes in the borehole are provided by selecting pairs of collars 10 and connecting the collars of each pair together by interengaging one with another the cooperating hinge portions 26, 27 and locating therein a corresponding hinge pin whereb the pairs of arcuate collars 10 are connected one to another.Each pair of collars 10 then has connected thereto by means of bolts 30 and corresponding nuts 31 a plurality of blades 11, the shank of each bolt 30 being inserted through a corresponding aperture 20, 21 of each collar 10 such that the head portion 32 of each bolt 30 is received in the recess 23 adjacent the corresponding aperture 20, 21 and the shank also extends through a corresponding aperture 28, 29 of each blade 11 connected to the collar 10, the connection being secured by means of nuts 31 screwed on to the respective shanks of the bolts 30. In this manner a cage is formed comprising two pairs of collars 10, each pair being connected to another pair by a plurality of blades 11 each connected at one end portion thereof to one pair of collars 10 and at a remote end portion thereof to another pair of collars 10.The cage is secured by ensuring that the hinge portions 26, 27 of each pair of collars 10 are connected so that each pair of collars 10 comprises an annulus for receiving a casing or pipe. The cages then are inserted in series axially in the borehole so that the outwardly bowed blades 11 engage a circumferential wall of the borehole whereby when a casing or pipe is received in the annular pairs of connected collars 10, the casing or pipe is centrally located in the borehole.

It will be appreciated that since the collars 10 and the blades 11 are secured one to another by means of the bolts 30 and corresponding nuts 31 and are not welded one to another, a disadvantage inherent in devices known hitherto for centralising casings and pipes in boreholes is eliminated.

It will also be appreciated that storage and transportation costs are reduced since storage and transportation of the components 10, 11, the bolts 30 corresponding nuts 31 and hinge pins requires less space than would be necessary if such components were combined to form erected devices.

Furthermore, it will be appreciated that the provision of a bolt 30 having a shank with an intermediate portion 34 of square cross section which corresponds with the dimension of each of the apertures 20, 21 and 28, 29 ensures that rotation of each bolt 30 about a central longitudinal axis thereof relative to a collar 10 and a corresponding blade 11 will not occur during screwing together of the bolt 30 and a corresponding nut 31. In consequence, only a single tool is necessary to screw together each bolt 30 and corresponding nut 31 since each nut 31 is applicable to a corresponding bolt 30 fro outside of a device being constructed.

Claims (5)

Claims

1. A device for centralising a component in an enclosure comprising a pair of annular members, a plurality of elongate members and means for connecting opposite end portions of the elongate members each to a corresponding one of the annular members so that the annular members are spaced one from another on an axis extending through the annular members.

2. A device as claimed in Claim 1 wherein the means comprises a plurality of bolts and corresponding nuts and each of the said members is provided with a plurality of apertures each for receiving a shank of a corresponding one of the bolts.

3. A device as claimed in Claim 2 wherein at least a portion of each shank is of rectangular transverse cross section and each of the apertures is of rectangular configuration whereby, when a shank of a said bolt is located in a said aperture of a member, angular movement of the shank relative to the member is restrained.

4. A device as claimed in Claim 3 wherein an inner surface of each annular member is countersunk adjacent each aperture.

5. A device for centralising a component in an enclosure substantially as hereinbefore described and as illustrated in accompanying drawings.