US3061010A

US3061010A - Locator for collars joining pipe lengths

Info

Publication number: US3061010A
Application number: US755253A
Authority: US
Inventors: Martin B Conrad; John B Mcelheny
Original assignee: MCELHENY
Current assignee: MCELHENY
Priority date: 1958-08-15
Filing date: 1958-08-15
Publication date: 1962-10-30
Anticipated expiration: 1979-10-30

Description

Oct. 30, 1962 M. B. CONRAD ETAL 3,061,010

LOCATOR FOR COLLARS JOINING PIPE LENGTHS Filed Aug. 15, 1958 4 Sheets-Sheet l 1- .4 IIIIIIIiiilllilllllllllllllli I r mam/MM ml N0 e wewwm Oct. 30, 1962 M. B. CONRAD ETAL 3,

LOCATOR FOR COLLARS JOINING PIPE LENGTHS 4 Sheets-Sheet 3 Filed Aug. 15, 1958 IINVENTORS.

Oct. 30, 1962 M. B. CONRAD ETAL LOCATOR FOR COLLARS JOINING PIPE LENGTHS T W44 44p 44% J4 United States Patent Ofiice 3 ,06 1,010 Patented Oct. 30, 1 962 3,061,010 LO-CATUR FER CULLARS JOINTNG PIPE LENGTH-IS Martin B. Conrad, Downey, and John B. McElheny,

Fullerton, Calif; said Conrad assignor to said Mc- Elheny Filed Aug. 15, 1958, Ser. No. 755,253 6 Claims. (Cl. 166-64) This invention relates to oil well casing; and more particularly to means for locating casing collars after the casing is in place.

Well casing comprises lengths of pipe, externally threaded at both ends and joined together by collars threadedly engaging these ends. The pipe lengths are not uniform; they may be as short as twenty feet or as long as forty feet. The pipe is sunk into the well, a length at a time.

By appropriate well-known means, the depth of significant oil-bearing strata encountered during drilling operations is determined; after the casing is in place, the well is logged by appropriate apparatus, so that the depths at which the collars are located with respect to these strata are determined. Now when it is desired, for example, to perforate the well casing at a definite level corresponding to a significant stratum, the perforator apparatus should be quite accurately positioned in the well, especially if the stratum is quite shallow.

It is one of the objects of this invention to make it possible to obtain such accurate positioning, utilizing the logged depths of the collars as reference points. For example, if the desired depth at which a casing perforator is to be used lies between two collars identified on the well log, then in accordance with this invention, a dog or the like lowered into the well, can be caused to engage either one or the other of the opposed edges of adjacent pipe lengths at one of the collars neighboring the desired location. Such engagement of the dog restrains movement of the dog in one or the other direction along the well. This restraint is translated into a definite signal, such as greatly increased resistance to raising or lowering of the collar locator.

Accordingly, it is another object of this invention to make it possible to engage the edges of the pipe lengths, and to release them, as desired.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of several embodiments of the invention. For this purpose, there are shown a few for-ms in the drawings accompanying and forming part of the present specification. These forms will now be described in detail, illustrating the general principles of the invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

eferring to the drawings:

TTGURE 1 is a View in elevation of apparatus incorporating the invention, and in well casing, the well casing being shown in section; the length of well casing being cut away to reduce the size of the figure;

FIG. 2 is an enlarged sectional view of the apparatus, shown in use in well casing, the position of the apparatus being such as to render detectable a casing collar by engagement of a set of dogs with the lower edge of a length of pipe;

FIG. 3 is a sectional view taken along a plane corresponding to line 3-3 of FIG. 2 and illustrating the retracted position of a second set of dogs which are adapted to cooperate with the upper edge of a pipe length;

FiG. 4 is a fragmentary view similar to FIG. 2, illustratin the first set of dogs in retracted position;

FIG. 5 is a fragmentary view similar to FIG. 3 but illustrating a dog in active tilted position, cooperating with the upper edge of a pipe length;

FIG. 6 is a view similar to FIG. 4, illustrating a dog of the first set in tilted active position and capable of cooperating with the lower edge of well casing, the apparatus being shown as it would appear during descent into the well;

FIG. 7 is a sectional view, taken along a plane corresponding to line 77 of FIG. 2;

FIG. 8 is a sectional view, similar to FIG. 2, of a modified form of the invention;

FIG. 9 is an enlarged fragmentary sectional view of the modified form, illustrating a dog in active position and cooperating with the upper edge of a pipe length;

FIG. 10 is an enlarged sectional view, taken along a plane corresponding to line 10- 10 of FIG. 8;

FIGS. 11 and 12 are sectional views taken along planes corresponding respectively to lines 1 1-"11 and 1212 of FIG. 10; and

FIG. 13 is a fragmentary sectional view, taken along a plane corresponding to line 1313 of FIG. 9.

Well casing 1 (FIG. 1) comprises a series of

pipe lengths

2, 3, 4, etc. joined by collars 5. These collars extend around the ends of the pipe lengths. As shown most clearly in FIG. 6, the adjacent pipe lengths are not in contact; their

opposed end edges

6 and 7 form shoulders capable of engagement to make it possible to deter mine the location of the ends of pipe lengths or of the collars joining them.

Apparatus is lowered into the well casing provided with two sets of dogs, a first set being adapted to engage downwardly directed edge 6 of a pipe length 2, as shown in FIG. 2. When thus engaged, there is a restraint against upward movement of the apparatus, and this is perceivable at the top of the well, as hereinafter described. Another set of dogs is adapted to engage the upper edge 7 of a pipe length, should it be desired to place a restraint against downward movement of the apparatus. However, but one set of dogs is active at any time, the other set being rendered inactive in a manner to be described.

The support for the two sets of dogs is provided by a pipe or tubing 8 threaded within a socket member 9. This socket member 9 in turn is threadedly connected to the upper end of a supporting body 10. Appropriate sealing means may be provided between the socket member 9 and the upper end of the body 10 as by the aid of O-ring 11. This ring is disposed in an annular slot formed in shoulder 10a engaging the upper end of body 10. Furthermore, as shown most clearly in FIG. 2, the lower end of the socket member 9 has a tapered conical cam surface 12 forming a continuation of the conical cam surface 13 carried by the body 10.

Adjacent its lower end, the body 10 carries a flange 14 having an opposed conical cam surface 15. These two opposed conical surfaces 12-13 and 15 are utilized for operating the dogs to disengage the

end edges

6 and 7 of the pipe length, all as hereinafter described.

The body 10 carries at its lower end a socket member 16 which may carry any appropriate apparatus. Between the Socket 16 and the flange 14 there is confined an annular bowed spring structure 17. This may be in the form of upper and

lower flanges

18 and 19 carried by spring elements 20 so bent as to form a crest 21 intermediate the

flanges

18 and 19.

Slidably mounted on the exterior cylindrical surface of the socket member 9 is a cage 22 (see also FIG. 7). A collar 23 is attached to the upper end of the cage member in any appropriate manner. It is in sliding contact with the socket member 9. The lower end of the cage member has an internally threaded aperture 24 into which is threaded the upper end of a skirt member 25.

This skirt has an internal cylindrical surface adapted to contact the crest 21 of the spring structure 17. An inwardly radially directed projection 26 is also formed on the skirt. This projection is adapted to ride over the crest 21 to compress the spring structure 17 as the projection passes from one side of the crest to the other. This produces a greatly increased resistance to relative movement between the cage member 22 and the supporting body member 10. The utility of this arrangement will be explained hereinafter.

The cage member 22 has an internal cylindrical surface 27 (FIGS. 3 and 7) spaced from support 10; but this surface is joined to cylindrical surfaces 28 and 29 (FIGS. 3 and 4) by the sloping

surfaces

30 and 31. These sloping surfaces are adapted to coact with the conical surfaces 12-13 and 15 to limit the sliding movement of the cage structure 22 with respect to the supporting structure 8910.

The cage structure is provided with slots within which are pivotally supported two sets of dogs. The first of these sets includes the diametrically opposite dogs 32 and 33 (FIGS. 2, 4 and 6). These dogs are located in slots 34 and 35 (FIG. 7) and pivoted by the aid of

pins

36 and 37 so that they may be tilted to the active position indicated in FIG. 2. Each of the

dogs

32 and 33 has an upper surface shown in FIG. 2 as in contact with the lower edge of pipe length 2. These dogs are furthermore urged toward the tilted active position by the aid of compression springs 38 located in sockets 39 in the cage structure 22. Struts 40 transmit the spring forces to the dogs. The upper portion of each

dog

32, 33 has a pair of apertures 32a32b and 33a-33b. The struts 40 engage the

outermost apertures

32a, 33a so as to cause the upper ends of both dogs to swing outward. These struts are urged outwardly of the socket 39 by the aid of the spring followers 41. T ese followers have ball and socket connections with the upper ends of struts 40. The lower ends of these struts are appropriately pivotally connected to the

dogs

32, 33.

In FIG. 6, these

dogs

32 and 33 are in tilted or active position, and they do not interfere with the downward movement of the apparatus. As these dogs pass the upper edges 7 of lengths of pipe, the springs 38 are compressed; the dogs being urged inwardly within the

slots

34 and 35.

However, upward movement of the tubular structure 8 will bring the

dogs

32 and 33 into engagement with the lower edge 6 of the first pipe length encountered.

In this upward movement there is sufficient friction between the spring structure 17 and the skirt 25 to move the cage structure 22 upwardly along with the tubular structure 8. As soon as the

dogs

32 and 33 engage an edge surface 6, the cage structure 22 is restrained from further upward movement. Accordingly, as the tube 8 and its associated parts move upwardly relative to the cage structure 22, the projection 26 carried by the skirt 25 passes over the crests of the spring structure 17. The pressure exerted by the projection 26 on the spring structure is'clearly perceptible at the top of the casing and indicates to the observer that a collar has been located. After the crest 21 is passed, the conical cam surface 15 engages the lower end of the

dogs

32 and 33 and urges them to the retracted position of FIG. 4.

Upward movement of the tubular member 8 relative to cage 22 causes outward tilting of another set of dogs 42, 43 (FIGS. 3, 5 and 7). These

dogs

42 and 43 are equiangularly spaced from

dogs

32, 33. They are pivoted in the same fashion as

dogs

32 and 33 but have downwardly directed engaging ends. In this case, however, the lower portions of the dogs are urged outwardly on their pivots by the struts 40. The

dogs

42 and 43 are identical with

dogs

32, 33, and likewise have two apertures 42a-42b and 43a--43b. Therefore, to urge these

dogs

42, 43 so as to assume the position of FIG. 5, the inner apertures 42b and 43b are engaged by struts against upward movement.

4 40. Accordingly, when the tube 8 has moved upwardly to the position of FIG. 4 (releasing dogs 32, 33), the second set of

dogs

42, 43 is placed in active position.

FIG. 5 thus illustrates one of these dogs of the second set in such position to restrain downward movement of the cage structure 22. In this position, the sloping surface 1213 has moved upwardly away from the dog 42, permitting the compression springs 38 associated with

dogs

42 and 43 to move them from the position of FIG. 3 to the position of FIG. 5.

Downward movement of the cage 22 is restrained as soon as

dogs

42, 43 engage an upper edge 7. From the position of FIG. 5, tube 8 can move downwardly. This movement ultimately causes the sloping

surfaces

12 and 13 to engage the upper end of the

dogs

42 and 43 and return them to the retracted position of FIG. 3 against the force of springs 38. Engagement of the sloping surfaces 1213 when the sloping surface 30 of the cage structure 22 limits this relative downward movement.

At the same time, the spring structure 17 has moved from the position of FIG. 5 to the position of FIG. 3. Again the projection 26 passes over the crests 21 of the spring structure, causing a definite indication at the top of the well that there is an obstruction to downward movement of the cage member 22. In other words, the upper end edge of a pipe length such as pipe 3 has been located.

The excursion of the tubing 8 between the limiting positions of FIGS. 3 and 5 thus alternately releases one set of dogs and retracts another set of dogs. In the position of FIG. 3, as hereinbefore explained, the

dogs

32 and 33 will be in the active position while the

dogs

42 and 43 are in the retracted or inactive position. The

dogs

32, 33, 42, 43 all have identical forms, simplifying manufacture. The struts 40, however, are so connected to them that in every instance the compression springs 23, 38 urge the dogs toward active position.

Furthermore, either ends of the dogs can be made to cooperate with the edges of the pipe lengths. For example, the lower ends are effective for

dogs

32, 33; and the upper ends are effective for

dogs

42, 43. This is made possible by making the dog outlines symmetrical about a line normal to the axis of the pivot for the dogs.

When the cage structure 22 is restrained against upward movement as in FIG. 2, the upward movement of the tubular member 8 causes ultimate retraction of the

dogs

32 and 33 to the position of FIG. 4 and at the same time the other set of

dogs

42 and 43 is placed in active tilted position, capable of engaging the upper end of a pipe length.

The manner of use of quite obvious from the foregoing. Assuming that the apparatus is in the position of FIG. 2, the tube 8 may be gradually lowered into a well. The

active dogs

32 and 33 then click past the

ends

6 and 7 of successive lengths of pipe until approximately the desired depth is reached between two collars to be located, the two collars being identified on the well log. Then the tubing 8 is pulled upwardly against gravity until the dogs 33 engage the lower edge 6 of a length of pipe. Further upward pull on tube 8 causes the crest 21 to pass from one side to the other of projection 26, thereby giving an indication that the cage member 22 is restrained This additional necessary pull may be of the order of thousands of pounds, as determined by the design of spring 17. It is thus easy to observe this condition, and thereby to know that a collar has been located at a depth corresponding to the length of the tubing 8 in the well.

After this occurrence, the relative position of the cage structure 22 and tube 8 is illustrated in FIG. 4.

Dogs

32, 33 are retracted, and

dogs

42, 43 are in active position (FIG. 5). Further upward movement simply causes the second set of

dogs

42 and 43 to click past the edges of the adjacent pipe lengths. However, downward movement of tubing 8 brings the

dogs

42 and 43 to the position of FIG. against the upper edge of the pipe 3. Here again, increasing the weight on tube 8 sufliciently to move the crest 21 of spring 17 past the projection 26 is an indication that the cage structure 22 has been stopped in its downward movement. The

dogs

42 and 43 are then urged by

cam surfaces

12, 13 to the retracted position as indicated in FIG. 3 and the first set of

dogs

32 and 33 are released by the cam surface 15 to tilt into active position, as illustrated in FIG. 2.

Up and down movement of the tube 8 can thus sense the location of the collars 5. By appropriate coordination with the log of the well, it is possible to locate those two collars which are signifiant in connection with the operation to be performed in the well.

In the form of the invention illustration in FIGS. 8 to 13, inclusive, only one set of dogs is utilized, and relative movement between the cage structure and the supporting structure is opposed not by spring pressure but by hydraulic means.

In FIG. 8 a set of three dogs (two of which are shown at 44 and 45) is in retracted neutral position. The dogs are equiangularly disposed about the axis of the cage structure 47. The tubing in this case includes an upper section 48 coupled as by a collar 49 to the supporting body 50. Carried on a reduced portion 51 of the supporting body 50 are the three cams 52 as by the aid of a ring 53 and machine screws 54 (see also FIG. 13).

The cam surfaces 55 in the position of FIG. 8 cooperate with corresponding surfaces 55a of the three

dogs

44, 45, etc. to retract them to the position of FIG. 8 against the pressure of the enclosed springs 56. Each of the

dogs

44, 45, etc. is located in its slot such as 57, 58.

The cage structure 47 at its lower end threadedly engages the upper end of a sleeve 59. At its lower end, the sleeve 59 has a flange 60 which operates as a piston in a surface 61 of cylinder structure 63. An appropriate sealing means such as the O-ring 62 may be provided between the surface 61 and the piston 60.

The upper end of cylinder structure 63 is threaded to receive a cap 64 that overlies the upper edge of this cylinder structure 63 and forms and end annular surface 74 for the cylinder surface 61. Cap 64 is sealed against the outer periphery of the sleeve 59, as well as against the cylindical surface 61. This may be accomplished by the aid of O-

rings

65 and 66.

The cylinder structure 63 includes a relatively thick lower head 67. This head 67 is connected by a lower hollow threaded extension 68 to a pipe or tube 69, the purpose of which will be hereinafter explained.

The surface 70 of the lower head 67 serves as an end surface for the cylinder space.

Also operating within the cylinder 63 is a flange 71, forming a piston integrally joined to the body 50. This flange or piston 71 may be sealed against the cylindrical surface 61 by the aid of an O-ring 72.

A cylinder chamber 73 is formed between the flange 71 and the surface 70 (see FIGS. 8, 11 and 12). When the flange 60 is spaced from the lower surface 74 of cap 64 (FIG. 9), there is another annular cylinder chamber 75 formed between the flange 60 and surface 74. Hydraulic fluid, in a manner to be hereinafter described, may be interchanged between these two

chambers

73 and 75, for controlling the retraction and tilting of the

dogs

44, 45, etc.

Let us assume that the member 69 is stationary, that is, by being bottomed in the well or by the aid of a packer carried by it. Thus, in order to move the

dogs

44, 45, etc. to the active position of FIG. 9, weight may be added to the tubing 48 so as to urge the liquid from the cylinder chamber 73 into the cylinder chambers 75 (FIG. 9). This interchange of liquid is effected through

ports

76 and 76a (see also FIGS. 10, 11 and 12) provided in the wall of the cylinder structure 63. The cylinder chamber 73 is in communication with port 76a by the aid of a check valve structure 77. This check valve structure may be quite conventional. It may include a cage 78 (FIG. 11) having a lower enlarged head 79' threaded into the bottom 67 of the cylinder 63. This cage provides a valve seat 80 at its upper end adapted to be engaged by the conical closure member 81 urged to closing position by compression spring 82. The cage 78 has a through port 78a communicating with port 76a and with the interior of the cage.

Appropriate sealing means such as O-

rings

83 and 84 are provided for the cage 78 to maintain fluid-tight seal between the cage and the wall 67. Furthermore, the clostn'e member 81 is carried by a stem 85 around which the compression spring 82 extends. The lower end of stem 85 is guided in head 79.

By making the spring 82 strong enough, a substantial resistance to the downward movement of the piston '71 is effected. This in turn means that the weight that must be imposed on tubing 48 to open the check valve 77 must be quite large. The rate at which relative movement is permitted between the stationary cylinder 63 and the support member 50 is also controlled by this check valve.

Flow of liquid past the check valve structure 77 to the port 76 causes liquid to be supplied to the interface between the flange 60 and the surface 74. Ultimately all the liquid from chamber 73 is accommodated in the chamber 75, as indicated in FIG. 9.

FIG. 11 illustrates an intermediate position of the piston or flange 71, being urged downwardly to force the liquid past the check valve structure 77. As this occurs, the flange or piston 60 is urged downwardly and ultimately into contact with the upper surface of the piston 71 as illustrated in FIG. 9.

Under such circumstances, the sleeve 59 being joined to the piston 60 moves downwardly and pulls the cage structure 47 away from the cam surfaces 55, permitting outward tilting of the

dogs

44, 45, etc.

Because the cylinder chamber 75 is long and narrow, as compared with the cylinder chamber 73, the piston 69 moves through a greater distance than piston 71 when there is an interchange of liquid between these chambers. This accordingly proivdes for a separation between the cam surfaces 55 and the dogs 45 to permit the dogs to be cocked to the position of FIG. 9.

The

dogs

44, 45 in the cooked position restrain the cage structure 47 from further downward movement upon engagement with an upper edge of a pipe length (FIG. 9).

After the dogs are thus cocked, the entire assembly may be moved upwardly to a desired depth. For this purpose, tubular member 69 is released so that it may move upwardly.

Now, when support 50 is pulled up, the cylinder 63 is also moved up by aid of the column of liquid in chamber 75 as

pistons

60 and 71 move in unison upwardly. Since only the weight of the cylinder 63 and attached pipe 69 is effective to urge the wall 74 toward piston 60, another check valve 86 (FIG. 12) effectively prevents escape of liquid from chamber 75 while the assembly is moving upwardly. The location and further function of this valve will be hereinafter described. Upward movement of the support 50 thus carries with it the sleeve 59 and the cage 47 in unison so that the outer lower ends of the

dogs

44 and 45 simply click over the edges of the pipe lengths as the dogs move past these edges.

When it is desired to observe the location of a collar, the upward motion is reversed and now the entire structure moves downwardly until the

dogs

44, 45, etc. are restrained by the top edge of a pipe length. Now the cylinder structure 63 is urged downwardly by the flange 71. Thus in this movement, the liquid is urged outwardly from the cylinder chamber 75 into the cylinder chamber 73. Check valve 86 is used for this purpose, illustrated in FIGS. 10 and 12. This check valvestructure 86 com- 7 municates with the port 76 via port 76b. It has a body 87 having a threaded head 88 engaging a threaded aperture in the head 67. The body 87 is sealingly accommodated in a bore 89 communicating with an inlet port 90 to the space 73.

The body 87 extends into a bore 89 in communication with port 90. The body 87 at its upper end has a seat 91 cooperating with a conical closure member d2 disposed above the seat. This conical closure member 92 is urged strongly downwardly to seated position by the aid of a strong compression spring 93 located in the bore 89. Closure 92 has a stem extending in the central port of body 87 and guided therein. A transverse port 8712 extends from the central port and communicates with port 76b.

-By appropriate choice of the spring 93, the resistance to downward movement of the piston 71, body 50, and the cylinder 63 may be made quite high. When this resistance is overcome by added weight, the valve closure 92 is unseated, and the liquid slowly moves via

ports

76 and 76b to the chamber 73 (FIG. 8). The greatly increased resistance to downward movement may be observed at the top of the Well to indicate that the

dogs

44, 45, etc. are in restraining position.

Ultimately the parts reach the position of FIG. 8. The cam surfaces 55 now retract the

dogs

44 and 45. The operations may now be repeated.

The inventors claim:

1. In a locator for collars joining tubular lengths of pipe: a support member; a cage surrounding the member and slidable thereon within limits; said cage having a slot or slots that extend longitudinally of the cage; a dog or dogs respectively pivotally mounted in said slot or slots whereby the dog or dogs may be tilted to engage the end edge of a pipe length or retracted to disengage said dog or dogs from said end edge and thereby respectively to restrain movement of the cage or to permit movement of said cage; said support member having a tapered surface adapted to engage the dog or dogs to retract the dog or dogs; resilient means for tilting said dog or dogs into engaging position, said cage having a surface corresponding to said tapered surface and engageable with the tapered surface on the support member for imposing a limit on the relative sliding motion; said cage having a skirt; a bowed spring structure of annular form carried by the support member and having a crest engaging the skirt; and a projection carried by the skirt and adapted to ride over the crest to provide a temporary increased resistance to sliding movement.

2. In a locator for collars joining tubular lengths of pipe: a hollow rigid support member of generally tubular configuration; the interior of said hollow member being unobstructed; a cage member slidably supported on the exterior of said support member; means for limiting relative sliding movement between the members; one or more dogs carried by the cage member and movable optionally to extend outwardly of the cage member or to be retracted therein; resilient means urging said one or more dogs outwardly; said dog or dogs being adapted, when in their outward position, to engage an end edge of a length of pipe as the support member and cage member are moved in one direction and thereby to arrest the movement of the cage member; means interposing a. resilient force resisting movement in said direction of the support member after the cage movement is stopped by the dog or dogs, comprising a spring structure carried by one of said members constructed to provide a maximum resilient resisting force against relative movement between the cage member and the support member, occurring intermediate said relative movement; and means carried by the support member for retracting the dog or dogs upon continued movement of the support member in said one direction.

3. In a locator for collars joining tubular lengths of pipe: a hollow rigid support member of generally tubular configuration; the interior of said hollow member being unobstructed; a cage member slidably supported for movement within limits on the exterior of said support member; one or more dogs carried by the cage member and movable optionally to extend outwardly of the cage member or to be retracted therein; resilient means urging said one or more dogs outwardly; said dog or dogs being adapted, when in their outward positions, to engage an end edge of a length of pipe as the support member and cage member are moved in one direction and thereby to arrest the movement of the cage member; a resilient structure encircling the support member and encircled by the cage member; means carried by one of the members to cause the resilient structure to be momentarily compressed when said support member is moved relative to the arrested cage member, said compression occurring at an intermediate point in the relative movement of the support member and cage member; and means carried by the support member for retracting the dog or dogs upon continued movement of the support member in said one direction.

4. In a locator for collars joining tubular lengths of pipe: a hollow rigid support member of generally tubular configuration; the interior of said hollow member being unobstructed; a cage member slidably supported for movement within limits on the exterior of said support member; one or more dogs carried by the cage member and movable optionally to extend outwardly of the cage member or to be retracted therein; resilient means urging said one or more dogs outwardly; said dog or dogs being adapted, when in their outward positions, to engage an end edge of a length of pipe as the support member and cage member are moved in one direction and thereby to arrest the movement of the cage member; a resilient structure encircling the support member and encircled by the cage member; said resilient structure having a crest intermediate its ends; means car-ried by one of the members for depressing the crest when said support member is moved relative to the arrested cage member, said compression occurring at an intermediate point in the relative movement of the support member and the cage member; and means carried by the support member for retracting the dog or dogs upon continued movement of the support member in said one direction.

5. In a locator for collars joining tubular lengths of pipe: a hollow rigid support member of generally tubular configuration; the interior of said hollow member being unobstructed; a cage member slidably supported on the exterior of said support member; means for limiting relative sliding movement between the members; a first set of one or more dogs carried by the cage member and capable of tilting and moveable into engagement with an edge of a length of pipe when the support member and cage member are moved in one direction; a second set of one or more dogs carried by the cage member and capable of tilting and moveable into engagement with an end edge of a length of pipe when the support member and cage member are moved in the other direction; resilient means for urging the dogs of the sets into tilting position; said dogs serving to arrest the movement of the cage member; means interposing a resilient force resisting relative movement of the support member and cage member after movement of the latter member is stopped by the dog or dogs, comprising a spring structure constructed to provide a maximum resilient resisting force against said relative movement occurring at an intermediate point in said relative movement; and means carried by the support member for retracting the dog or dogs upon continued movement of the support member after movement of the cage member is stopped by the dog or dogs.

6. In a locator for collars joining tubular lengths of pipe: a hollow rigid support member of generally tubular configuration; the interior of said hollow member being unobstructed; a cage member slidably supported within limits on the exterior of said support member; a first set of one or more dogs carried by the cage member and capable of tilting into engagement with an end edge of a length of pipe when the support member and cage member are moved in one direction; a second set of one or more dogs carried by the cage member and capable of tilting into engagement with an end edge of a length of pipe when the support member and cage member are moved in the other direction; resilient means for urging the dogs of the sets into tilting position; said dogs serving to arrest the movement of the cage member; said support member having two surfaces limiting the relative sliding movement of said support and cage members, each said surface being also adapted to urge respective set of dog or dogs to retracted position upon completion of said relative movement in one direction for one surface and one set of dog or dogs and in the other direc- 10 tion for the other surface and the other set of dog or dogs; a resilient structure encircling the support member; and means carried by one of the members to cause the resilient member to be momentarily compressed at an intermediate point in said relative movement, for either direction of relative movement.

References Cited in the file of this patent UNITED STATES PATENTS 2,091,750 Brown Feb. 27, 1940 2,199,020 Barrett et a1. Apr. 30, 1940 2,280,769 Page Apr. 21, 1942 2,380,022 Burt July 10, 1945 2,613,746 Whitney Oct. 14, 1952 2,741,316 Long Apr. 10, 1956 2,746,550 Mitchell May 22, 1956 2,856,007 Fredd Oct. 14, 1958 2,924,278 Garrett et a1. Feb. 9, 1960