GB2064121A

GB2064121A - Fixed gauge

Info

Publication number: GB2064121A
Application number: GB7933076A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-09-24
Filing date: 1979-09-24
Publication date: 1981-06-10
Also published as: GB2064121B

Abstract

An end measuring rod for use in testing inter alia the straightness and cross-sectional circularity of pipes and pipe assemblies for oil/gas wells and drilling rigs, comprises a plug 5 of resilient material attached permanently or releasably to one or each end of a hollow metal hard plated cyclinder 1 to protect the latter from impact damage during said tests. The length and diameter of the metal cylinder are specific to the internal diameter of the pipe or pipe assembly to be tested and the projecting length and diameter of the or each plug member are selected such as not to interfere with correct testing which is, in effect, performed solely by the metal cylinder. <IMAGE>

Description

SPECIFICATION Drift mandrel This invention relates to drift mandrels for use in connection with pipes and pipe assemblies, e.g.

to test the straightness and/or uniform circularity of pipes and pipe assemblies used in oil or gas exploration and recovery. In such tests, the drift mandrel is allowed to fall under gravity through the interior of the pipe or pipe assembly.

The conventional drift mandrel used in an oil rig for testing the longitudinal straightness, circularity, bore uniformity and lack of inward deformation of pipes and pipe assemblies comprises a hollow steel cylinder having planar steel discs welded to each end, the cylinder length, L, and outside diameter, D, being specific to the inside diameter of the pipe or pipe assembly to be tested (e.g. as specified by the American Petroleum Institute, API Table 6.11). To ensure that the appropriate clearance allowed between the drift mandrel and the pipe or pipe assembly is sufficient, i.e. the installed string of pipes and/or pipe assemblies will still permit the passage therethrough of the required tools, the dimensions of the drift mandrel used for the preinstallation tests must be accurate at the outset (i.e. initially) and must be maintained accurate for as long as possible in use to delay the need for replacement of the drift mandrel. Furthermore, use of the drift mandrel should not damage the interior of the pipe or pipe assembly, particularly any interior seals, threads or other coupling formations.

With the drift mandrels available to date, the initial accurate dimensions have only been achieved with difficulty (if at all) since welding the end discs to the cylinder ends tends to result in a local deformation of the cylinder (the outer diameter of which should preferably not be less than nominal D and should preferably not exceed nominal D + 0.005 in or nominal D + 0.13 mm).

Moreover, the arris between the cylinder and each end disc is liable to burring or having burred edge, either as a result of the welding operation or as a result of use of the drift mandrel. This again leads to dimensional inaccuracy of the drift mandrel and also can give rise to damage of the pipe interior by a test procedure.

Accordingly it is desirable to provide a drift mandrel whereby one or more of the abovementioned and/or other disadvantages is or are obviated or at least minimised.

According to this invention there is provided a drift mandrel comprising an elongate metal body having a cylindrical outer surface and at one or each end of the metal body a resilient end member.

Preferably the or each resilient end member is releasably attached to the metal body, e.g. as by a bayonet-type coupling or by means of cooperating screw threads. Alternatively, the or each resilient end member is permanently attached to the metal body. Conveniently in the latter case and with a resilient end member at each end of the metal body, the said metal body is hollow and the two resilient end members are interconnected internally of the hollow metal body.

Preferably the diameter of the elongate metal body is greater than that of the or each resilient end member, the length of said metal body being that specified for the particular diameter bore to be tested.

Preferably the difference, y, in diameter between the body and the or each end member is provided by the relationship y/x = 4LC/(L2 - 4c2) where x is the length of the end member (at said diameter), L is the specified length of the metal body, and c is the clearance allowed between the drift mandrel and the bore to be tested, i.e. equals the interior diameter of the pipe or pipe assembly minus the specified drift mandrel diameter D.

From this relationship it will be appreciated that the diameter difference y may be reduced if the length of the or each end member is reduced correspondingly, i.e. by the same factor, and vice versa must be increased by the same factor as the said length is increased.

By way of non-limiting example, embodiments of this invention will now be described with reference to the accompanying drawings of which: Figure 1 illustrates schematically, in longitudinal cross-section, a drift mandrel according to this invention in a first embodiment thereof, Figure 2 is an exploded perspective view of parts of the drift mandrel of Fig. 1, Figure 3 shows in side elevation part of a drift mandrel according to this invention in a second embodiment thereof, and Figures 4 and 5 show in longitudinal crosssection part of drift mandrels according to this invention in respectively third and fourth embodiments thereof.

The exemplary drift mandrel 1 of Figs. 1 and 2 comprises a hollow cylindrical steel body 2 of length L and outer diameter D, the values of L and D being appropriately specific to the pipe 10 to be tested and leaving the desired clearance 'c'. The body 2 is accurately cut to the length L from cold drawn seamless steel tubing and is externally electroplated with nickel and/or chromium (for hardness and corrosion resistance) to provide an actual value of D that is the nominal or specified value -- 0.000 in to + 0.005 in (i.e. -0.000 mm to + 0.13 mm). The inner surface of hollow body 2 is machined or otherwise formed at each end with a pair of diametrically opposite, likewise orientated grooves 3 of j-like bayonet configuration.To each end of body 2, there is attached a resilient plug member 5 formed in a mold (by casting or molding) to have a pair of diametrically opposite, radially directed, outwardly projecting pins 4 co-operable with the bayonet grooves 3. The pins 4 project from a cylindrical part 6 of plug member 5, said part 6 having a diameter corresponding to the inner diameter of body 2 and extending from a generally hemispherical part 7 of the plug member that projects outwardly beyond the respective end of body 2. The said part 7 has a portion 8 extending for a length x adjacent part 6 and of a constant diameter equal to the maximum diameter of part 7 but less than the outer diameter D of body 2 by an amount y.

The resilient material employed for moldformation of each plug member 5 is preferably an elastomer of appropriate abrasion resistance, e.g.

an epoxy-derived urethane polymer or copolymer (such as that obtainable from Wright 8 Sumner Ltd., 55 Argyll Street, Kettering, Northants, England under reference CUE 02036). If desired the mold-formed plug member 5 may be internally reinforced as by textile or like fabric material, by a metal mesh or perforated strip, or by glass fibre material. Alternatively, if additional resiliency is desired, plug members 5 may be hollow formations for example formed by rotational casting (e.g. in accordance with UK Patent No. 1434345).

In the modified embodiment of Fig. 3, the grooves 3 are replaced by correspondingly shaped slots 13 extending through the wall of body 2, the plug 5 being attached to body 2 by intercoupling, in bayonet fashion, the pins 4 and slots 13. Thus, in like fashion to the embodiment of Figs. 1 and 2, the embodiment of Fig. 3 provides for the releasable attachment of the plug members 5 from the ends of body 2. A like result may be achieved by omitting the pins 4 and providing body part 6 with a mold-formed screw thread cooperable with a corresponding screw thread formed on the inner surface of body 2 in place of the grooves 3 or slots 13 (see Fig. 4).

In an alternative construction, shown in Fig. 5, the plug members 5 may have pins 4 omitted and be attached by their parts 6 to the ends of body 2 by being force fitted therein and/or by bonding thereto (e.g. as by adhesive). Preferably in such an arrangement the two plug members 5 are interconnected by a metal or plastics material tie rod extending internally of body 2 such that in use the stress on one plug member is to some extent taken up by the other and resists any tendency for a pressure increase within the drift mandrel to decouple the plug member remote from the impact end.

It will be appreciated from Fig. 1 that the length of the drift mandrel 1 exceeds the specified L by at least the distance x. Thus if the diameter of the extended portions provided by plug members 5 were identical to the diameter D of the body 2, the drift mandrel would be more readily obstructed, e.g. by longitudinal curvature and/or cross sectional ovality, than would be warranted by a drift mandrel of total length L. Accordingly the maximum diameter of projecting part 7 of each plug member 5 is less than diameter D by a distance y. A relationship between x and y in relation to L and D can clearly be established and, empirically, such a relationship might be derived as follows (reference being had to Fig. 1): R=r+D+c Also R2 = (L/2)2 + (r + D)2 so that substituting for R one obtains r = (L2 - 8cD -- 4c2)/8c Furthermore, tan a = L/(2r + 2d) = y/x so that substituting for r one obtains y/x = 4Lc/(L2 - 4c2).

In tests of a drift mandrel according to Fig. 1, the plug members 5 provided effective long-term protection against impact damage to the ends of body 2, and ultimately were readily replaceable with fresh plug members 5 by means of the bayonet coupling 3, 4 thereby prolonging the useful life of the main body 2 of the drift mandrel.

Claims

1. A drift mandrel comprising an elongate metal body having a cylindrical outer surface and at one or each end of the metal body a resilient end member.

2. A drift mandrel according to Claim 1, wherein the or each resilient member is releasably attached to the metal body.

3. A drift mandrel according to Claim 1 or Claim 2, wherein the or each resilient member is releasably attached to the metal body by a bayonet-type coupling.

4. A drift mandrel according to Claim 1 or Claim 2, wherein the or each resilient member is releasably attached to the metal body by means of co-operating screw threads.

5. A drift mandrel according to Claim 1 wherein the or each resilient end member is permanently attached to the metal body.

6. A drift mandrel according to Claim 1 wherein a said resilient end member is permanently attached to each of the two ends of the metal body, the metal body is hollow from end to end thereof, and said two resilient end members are interconnected internally of the hollow metal body.

7. A drift mandrel according to any preceding Claim, wherein the diameter of the elongate metal body is greater than that of the or each resilient end member, the length of said metal body being that specified for the particular diameter bore to be tested.

8. A drift mandrel according to Claim 7, wherein the (minimum) difference, y, in diameter between the metal body and the or each end member is provided by the relationship y/x = 4Lc/L2 - 4c2) where x is the length of the end member (at said diameter), L is the specified length of the metal body, and c is the clearance allowed between the drift mandrel and the bore to be tested, i.e. equals the interior diameter of the pipe or pipe assembly minum the specified drift mandrel diameter D.

9. A drift mandrel according to any preceding Claim, wherein the or each resilient end member comprises an elastomeric resilient material.

10. A drift mandrel according to Claim 9, wherein said material comprises an epoxy-derived urethane polymer or copolymer.

11. A drift mandrel according to any preceding Claim wherein the metal body is an externally electroplated, cold drawn, steel tube.

12. A drift mandrel substantially as herein described with reference to and/or as illustrated in the accompanying drawing.