US2638316A - Power unit for a well pipe slip assembly - Google Patents

Description

May 12, 1953 G. E. MuLLlNlx 2,638,316

POWER UNIT FOR A WELL PIPE SLIP ASSEMBLY Filed Jan. 14, 195o 5 sheets-sheet 1 6*/@0 E. Maa/wx,

INVENToR.

May 12,1953 l G. E. MULLINlxl 2,638,316

POWER UNIT FOR A WELL PIPE SLIP ASSEMBLY Filed Jan. 14, 195o a sheets-sheet 2 6?@0 6'. Mll/HAY, INVENTOR..`

May 12," 1953 G. E. MULLlNlx 2Q-'638,316

PowER UNIT FOR A wELL PIPE sLIP ASSEMBLY 5 Sheets-Sheet 5 Filed Jan. 14, 1950 67@ E. MUL ///X,

IN VEN TOR.

May 12, 1953 ci. E. MULLlNlx 2,638,316

PowER UNIT FoEAwELL PIPE SLIP ASSEMBLY Filed Jan. 14, 1950 5 Sheets-Sheet 4 I 9 I Q E L! 'CNG G N Nr 2P E $9@ l L9 X Q "m /Y /Y /X/ w N if m s, C H L m an@ 0,1 l m io O O\NQ om 91 mags j u O m K9 G/eo E. Maa/Mx,

s IN VEN TOR.

5% www May 12, 1953 G. E. MULLlNlx POWER UNIT FOR A WELL PIPE SLIP ASSEMBLY 5 Sheets-Sheet 5 Filed Jan. 14, 1950 NWQ Q Patented May 12, 1953 UNITED STATE POWERv UNIT FO s PATENT OFFICE R A WELL PIPE SLIP SSEMBLY Application January V14, 1950, Serial No. 138,58

This invention relates to the well drilling art and is directed to` improvements in well pipe supporting apparatus. This invention nds particular usefulness in connection with power units for raising and lowering pipe yslip assemblies with respect to a slip bowl.

In the well drilling art it is common to employ a drill string for rotating a bit, the drill string being formed of a plurality of pipe sections joined end-to-end by threaded connections. The bit becomes dull and must be withdrawn at intervals from the bore hole for replacement. The threaded jointsbetween the pipe sections are customarily connected by supporting the lower portion of the pipe string by means of a plurality of wedge-shaped slips which are received within a stationary slip bowl. An upper section of pipe is then connected by turning it with respect to the lower portion of the drill string. -The slips and slip bowl are also employed for supporting and rotating the lower portion of the drill string when the pipe joints are to be disconnected. f Although such slip assemblies are ordinarily moved by hand to and lfrom operative position within the slip bowl, power operated devices have beenused with some success for performing this operation. The use of power leliminates the necessity of repeatedly liftingthe slip assembly out of the slip bowl by hand. r Fatigue of the crew members operating such assembly is thereby greatly reduced, and the crew members remain more alert to possible danger in the operation of the rig equipment.

y One of the objects of my invention is to provide a power unit for use in raising and lowering `pipe supporting slip assemblies, the power unit employing novel means for lifting and guidinga tubular post or column which carries the off-center weight of the slip assembly by means of a laterally extending arm secured to its upper end.

Another object is to provide a power lift device of this type having novel construction so that a minimum over-all height is achieved.

Another object is to provide a lift device of this type which is effective both for raising and for lowering the slip assembly under power.

Another object is to provide a power operated lift device for a well pipe slip assembly'which includes a lift column pivotally supported so that it may swing the slip assembly and kcarrier arm laterally to an inoperative position on the derrick floor. A

A related object is to provide a device of 8 Claims. (Cl. 254-93) this type vhaving a novel form of rotation latch device.

Another object is to provide a tubular post or lift column which is subject to bending forces applied bythe weight of the lateral arm and slip assembly, and in which the outer surface of the columnv is used for guiding the column for axial movement, and wherein the inner bore of the column is employed in connection with Athe stationary piston for Amoving the column by fluid pressure.

A further object of this invention is to provied a novel form of connection for securing the laterally extending arm to the upper end of the lift column.

Other objects and advantages will appear more fully hereinafter. y

In the drawings:

Figure 1 is a side elevation partly broken away showing a rotary machine, a pipe slip supporting assembly, and a power unit for actuating said assembly, the power unit comprising a preferred embodiment of my invention.

Figure 2 is a top plan View thereof partly broken away Figure 3 is a sectional elevation of the power unit taken substantially on the lines 3-3 as shown in Figure 2.

Figure 4 is a sectional plan view taken substantially on the lines 4-4 as shown in Figure 3.

Figure 5 is a sectional plan view taken substantially on the lines 5--5 as shown in Figure 3.

Figure 6 is a sectional plan View taken on the lines 6 6 as shown in Figure 3.

Figure '7 is a sectional elevation partly broken away taken substantially on the lines 'l--l as shown lin Figure 5.

Figure 8 is a fragmentary sectional plan view showing the head member in tilted position with respect to the lift column.

Referring to the drawings, the power unit generally designated lli comprises in general an upright frame il from which a vertical lifting post or column l2 projects. The post l2 is guided for reciprocation within the frame and carries a head member it at its upper projecting end'. Laterally projecting arm I4 connects the head I3 to a support structure I5 which carries a unitary slip assembly It. rlhe slip assembly I6 is movable into operative position within the slip bowl I'I provided on the master bushing I8 of the rotary machine i9. A preferred type of slip assembly I6 and support structure l5 is shown and described in my copending application, Serial No. 138,588, filed January 14, 19501. Another type of slip assembly and support structure is shown in my copending application, Serial No. 660,679, filed April 9, 1946, now issued as Patent No. 2,575,356, dated November 20, 1950.

The function of the power unit I8 is to raise and lower the support structure i and slip assembly I5 in order to set the slips for'supporting a well pipe 20.

The rotary machine I9 may be of any standard design and rests upon the usual supporting struc:- ture (not shown). A mounting flange 2I is provided on the base of the rotary machine I9 and supports a mating flange 22 by means of bolts 23. The mating flange carries a sub-base M which in turn supports the upright frame Hl and is connected thereto by means of bolts 2S.

As shown in Figures 3-7, the tubular column or lifting post I2 comprises a cylindrical member closed at its upper end and mounted for vertical reciprocation within the frame Il. The post I2 is relatively large in diameter in order to withstand without undue deflection the oli-center or side load imposed by the weight of the supporting structure I5 and unitized slip assembly IG. The post is guided on its outer periphery by roller elements carried on the frame and is raised and lowered by fluid pressure acting within its in` ternal bore 26. An axially immovable piston rod assembly 27 extends upwardly into: the bore 216 and carries a piston 28 at its upper end which forms a sliding seal within the bore 2B. The piston 2S divides the bore 26 into an upper pressure chamber 29 and a lower pressure chamber 3G. The piston assembly 2' comprises a pair of concentric tubes SI and `32 which cooperate to denne an inner fluid passageway 33 and an annular fluid passageway S4. The outer tube 32 is provided with an annular shoulder 35 which rests on the thrust bearing assembly 36. rThis assembly 3S is carried on the base plate 3'7 which is attached to the frame il` by means of bolted connections 38'. The lower end of the outer tube 32 extends downwardly through the bore t2k in the base plate 37 so that it may rotatel relative to base plate 37. A snap ring 49 on the lower projecting end of the outer tube- 32 maintains the parts in assembled relation.

The inner tube 3l is enlarged at each end to nt within the bore of the outer tube 32 and` to form a seal therewith. The annular passageway 34` communicates with a port 38 in the outer tube 32 to establish communication with the lower pressure chamber 30. The annular passageway 34 also communicates with lateral ports $0 formed in the Wall of the outer tubeV` 32 and with an annular recess 4I provided in the wall of the central bore 42 of the base plate 37. A passage 43 in the base plate 37 communicates with the annular recess 4I and with suitable piping connections 34. Similarly, the inner passageway 33 communicates through ports 45 in the Wall of the outer tube 32 with an annular recess 48 formed adjacent the bore 42 in the base plate 37. The passage 47 in the base plate 37 communicates between the annular recess 4S and the pip'- ing. 48. From this description it will be understood that the piping 48 communicates via the passage 47 and inner passageway 33 with the upper pressure chamber 29, while the piping 4d communicates via passage 43 and annular pas-'- sageway 34 to the lower pressure chamber 3U.

The lower end of the lower pressure chamber 30 is defined by a cylinder head 5B which is received within the lower end of the tubular post I2 and held in position against an annular shoulder 5I by means of a snap ring 52. The cylinder head 5|] is provided with a central bore 53 for a sliding reception of the outer surface of the outer tube 32 on the piston rod assembly 27. An outer sealing ring 54 prevents leakage of fluid between the cylinder head 50 and the tubular post I2, and an inner sealing ring 55 prevents leakage between the cylinder head 5i) and the outer surface of the outer tube 32.

A four-way control valve 56 is provided at a convenient elevation and connected by suitable piping to the line li-i and lit, as well as to a vent and a pressure supply source (not shown) When the four-way valve 5t is turned to one position iiuid pressure is admitted to the upper pressure chamber 29 and exhausted from the low pressure chamber 30 so that the post I2 is raised. When the four-way Valve 5E is turned to another position the fluid pressure is admitted into the lower pressure chamber 30 and exhausted from the upper pressure chamber 23 so that the post l2 is moved downwardly under power.

Suitable guide means are provided for Guiding the post. I2 with respect to the frame II. As shown in the drawings, this means includes three guide roller assemblies B0, 6I and 62 mounted within the upper portion oi` the frame or housing II and a pair of rollers 63 mounted upon trunnions 64 provided on the ring generally designated 65. The ring 65 is carried on the lower end of the plungerv and the rollers 63 are disposed within vert-ical trackways 66 provided on opposite sides of thel frame I I. The three guide roller assemblies 60, Si and 62 are mounted on a support plate 67 which is in turn secured to a flange 68 of the frame II as by stud bolts U8 (see Figure '7). As shown particularly in Figure 5, the plate 67 is generally U-shaped in plan. view and the three guide roller assemblies are disposed thereon and substantially equally spaced about the post I2. The front or main guide roller assembly 30 comprises two vertically spaced rollers 'I0 carried upon shafts 'il supported within a bifurcated bracket element 72'. A bore 73 is formed in the bracket element 72 to receive a supporting shaft 74, the ends of said shaft being. secured within spaced lugs 75 formed at opposite sides of. the open end of the support plate 67. rEhe other two guide roller assemblies Si and 62 are substantially identical to one an other, each including a single roller 76 carried by shafts 77 and 78 respectively. The ends of these shafts are supported within upstanding spaced lugs 79 on the plate 67. All four rollers are substantially identical and are provided with friction-reducing needle-type bearings 8B. It will. be noted that the face' of each roller is contoured to conform to the outer cylindrical Surface of the tubular post I2, whereby a maximum bearing surface will be presented by said rollers to the surface of said post. The main guide roller assembly 60 is preferably provided with two rollers as shown, rather than a single roller, inasmuch as said main assembly is subjected to considerably greater lateral force from the post I2 than either of the other guide roller assemblies GI and 52, especially at such time as the slip assembly I6 is being raised from the master bushing bowl I7.

As shown in Figure 7, they support plate Si includes an integraly depending threaded boss BI carrying a downwardly extending stop bolt 82. This bolt is provided with a lock nut 33. The function of this stop bolt 82 is to limit the up-v ward stroke off the post I2C. A resilient bumper element 84 is secured to the trunnion' ring 65,l which'bumper element is adapted to engage the head of said stop bolt.

I The trunnion ring or guide ring 65 is rotatably carried by the lower end of the post I2 by means of the ball bearing assembly 85. As shown in Figure 6, access is provided to the bearing raceway 86 by means of a removable plug 81, and the individual balls 88 of the bearing assembly 85 are introduced into the raceway 86 through the opening normally closed by the plug 81. A fitting 89 is provided at oneside of the ring 65 whereby lubricant may be supplied to said bearing assembly. A pair of O-rings 90 disposed in annular grooves formed in the guide ring 65 on either side of the bearing assembly 85 retain lubricant supplied through fitting 89 and also to prevent the entrance of foreign matter. The rollers 63 turn upon roller bearing assemblies 9| provided upon the integral trunnions 64 carried on the ring 65. i

, Thetrunnions are axially bored at 93 whereby a part of the lubricant supplied through fitting 39 may reach the bearings 9| of the two rollers 63. End covers 94 direct lubricant into the bearings 9|. The vertical trackways B6 are defined by two pairs of ribs 95, which pairs of ribs constitute integral inward extensions of the inner wall of the frame It will be noted that the rollers v(i3 each include a flange 95 adapted to abut the inner surfaces 91 of the ribs so as to prevent more than a slight amount of lateral movement of the bottom of the post I2 in a direction toward either pair of ribs 95.

The post I2 must normally be locked against rotation with respect to frame in order that the slip assembly I6 will remain in substantial vertical alignment with the master bushing bowl I1. For this purpose the guide ring 65 is provided with a pair of spaced lugs 98 adapted to support the ends of a shaft 99 upon which is pivotally mounted a latch |00. The upper portion of this latch includes a tongue |0| which is normally disposed between a pair'of spaced lugs |02 formed on a latch ring |03, which latch ring is rigidly secured to the post I2, as by welding, just above the guide ring 65. A torsion spring |04 carried by shaft 99 serves to constantly exert an inward or closing force upon the latch |00. To release said latch whereby the post will be free to turn with respect to the frame, the post is moved upwardly so as to dispose the latch |00 adjacent a hinged door |05 formed at the rear of the frame II. rPhe door |05 is then opened to permit a crew member to reach into the frame and pull the upper part of the `latch |00 -outwardly whereby the tongue IOI will be displaced from between the lugs |02 and the post will be free to rotate. When unlatched, the tongue |0I will ride upon the outer periphery of the latch ring |03. At such time as thepost I2 is turned back to its normal vposition said tongue will automatically snap back into latched position under the influence of the spring |04.

The piston 28 is free to rotate in unison with the post I2 by virtue of the rotatable connection of the pistonrod assembly 21 to the housing base plate 31. Hence, the lower packing ring |06 o-f said piston, when expanded by the uid pressure within the lower pressure chamber 30, will not restrain rotation of the post I2. It will be seen that the aforedescribed construction makes it possible to move the slip assembly |6 into an inoperative position clear of the rotary `'machine I9 when not in' use by rotating the slip assembly support structure I5 about thevertical axis of the post I2. M

As shown in the drawings, the frame II does.v

not comprise a single integral member but rather comprises a main body IIO having a footing I2 I, a detachable access panel I I secured to said main body as by bolts ||2 and having the hinged ,door |05 mounted thereon, and a top cover I|3. The top cover |I3 is shown secured to the support plate .61 by removable cap screws II4. These various components of the frame I I cooperate to form an enclosure I5. The bottom rear portion of the frame may be left open as atv |I6 to provide :easy access tothe enclosure II5. The door |05 on the access panel |II may be pivotally mounted upon an inclined hinge structure |01 so that said door automatically shuts by gravity. With particular regard to the top co-ver ||3, it will be seen that a resilient wiper element I|1 is secured centrally thereto to prevent the entrance of foreign matter into the frame enclosure II5.

The head member I3 interconnects the upper end of the post I2 and the end of the laterally extending support arm I4. The head member I3 comprises, generally, a platform element llt` rigidly secured, as by welding, to the upper end of the tubular post I2, and serves to close the upper end of the bore 26 in the post. A mounting cap I9 is pivotally supported upon said platform element |8 by means of a horizontal pivot bolt |29 and is provided with a mounting flange |22 to Whichthe end of the laterally extending arm I4 -is adapted to be rigidly secured as by bolts |23. A horizontally slidablelatch member |25 cooperates with a pivoted link |25, as described in detail hereinafter, to releasably latch the mounting cap I I9 against pivotal movement relative tothe platform element I I8 about the axis of pivot bolt |20.

The front portion of the platform element includes an .internallythreaded boss |26 which receives a downwardly extending stop bolt |21. This bolt |21 is vertically adjustable with respect to the platform element and is provided with a lock nut |28. The function of this stop bolt is to limit the downward travel of post I2 by the en-` gagement of the bolt head with a resilient bumper element |29 secured to the top of the frame I An upstanding spring mount |30 is also formed at the front portion of platform element I I8. The platform element I I8 is formed at its midportion with a pair o-f upstanding spaced lugs I3| which support shaft bolt |20. The platform element is formed at its rear portion with a pair of laterally extending spaced lugs |32 which are adapted to receive the ends of a link shaft |33. The mounting cap ||9 is of generally'circular configuration in plan view except for the elongated mounting flange I22` f-or arm lil. Said cap includes a pair of shaft bolt lugs |34 bored to receive shaft bolt |20. A pair of laterally extending spaced lugs |35 are formed upon the rear side walls of the cap and are bored for the reception of the ends of a shear pin |36.

The link |25 pivotally receives the central portion of the shear pin |36. An elongate bore |31 formed at the front portion of said link accommodates the lcenter portion of the link shaft |33. It will be noted that the upper front porti-ons of link |25 include a pair of lateral extensions |38 which overlie and rest upon the pads |50 provided upon the platform element II8. Accordingly, counterclockwise pivotal movement of the mounting cap ||9 about the axis of shaft bolt |20 is normally prevented, inasmuch as such movement assente' is resisted by the shear pin I. It. should be noted that the shear pin |36 is purposely made relatively small and of insufficient strength to withstand a severe shock or blow, so that in the event they arm M of the slip assembly support structure l5y is inadvertently subjected to an excessive load in either upward or downward direction, said shear pin tt. will fail and allow the mounting cap ||9` to pivot clockwise or counterclockwise about the axis of shaft bolt |23.

The latch member |25 is disposed lbetween the upstanding lugs |3| of platform element ||8 and includes a latch lug |39 at its rear portion and a spring chamber It@ at lits front portion. An elongated slot 54| formed in said latch |215 accomm-odates the center portion ci the shaft bolt |20 whereby horizontal movement of said. latch |24 toward or away from the link |25 is permitted, said latch Abeing adapted. to slidel upon the nat surfaces |42 formed upon the platform element ||8. A compression spring |43 disposed between the spring mount |36 of the platform element and the end wall of the spring chamber |40 serves to constantly urge the latch |26 toward the link |25. As shown in Figures 3 and; e, the top surface |44- of the upper front portion of said link |25 normally abuts the underside of the latch lug |39 on the latch |24. Accordingly,. the mounting cap H9 is normally restrained against clockwise pivotal movement. about the axis of shaft bolt |20. However, it is` possible to release the iront portion of said. link |25 from engagement with the latch lug |33 by moving the latch |21!V yin a direction away from said link 25. rlhis is accomplished by inserting a suitable tool (not shown) through an aperture |115y formed in the rear side Wall of the mounting cap HS so as to engage the end surface of the latch lug and force the latch |24 toward the front portion of the mounting cap H9. It is then possible to pivot the mounting cap clockwise about shaft. bolt |213 inasmuch as said link |25 will then be free to swing about the shaft |33, as shown in Figure 8. As soon as the front portion of the link |25 has been raised a short distance the latch |214 may be released, inasmuch as the .forward end lits ci the linkwill then abut the rear end surface |41 of the latch lug |39. As the front of the mounting cap il!! continues to rise, the link |23 becomes disengaged from the latch its.. At this' time the head member elements will assui'ne the position shown in Figure 8, the spring' |183 having returned' latch |24v to its normal position.

When the mounting cap I9 is pivoted counterclockwise to: lower the arm lll, the iront of the link |25 will also gradually be lowered until the forward end surface |48 thereof engages the rear end surface la? ofthe latch lug |39. Thereafter, as the result of this. engagement the latch |24 will be cainmed toward the front portion of the cap 9 against the resistance of spring |43 until such time as the top surface IM of said link assumes a lower elevation than the bottom surface |48' of said latch lug, whereupon the latch Will automatically snap back into its normal position.

It should be understood that this construction makes it possible: to raise the slip assembly |6 and its support structure i5 with. respect to the post i2. This feature may prove very desirable atsuchtime as the slip assembly t5 is to be moved to an inoperative position clear of the rotary machine I9. It will also be understood that the normal procedure in so moving the slip assembly involves raising the pos-t l2 so as to dispose the said latch |00, then swinging the arm I and slip assembly i6 about the axis of the post I2 tor a point preferably directly behind the frame It occasionally happens, however, that certain drilling apparatus or equipment will be disposed upon the derrick floor on the arc path to be traversed by thas-lip assembly, said equipment being of such a height as to interfere with thernovernent of said slip assembly. In thisv situation the latch |214 within head I3 may be disengaged so as to release mounting cap H9 for pivotal movement about the bolt |20 whereby a catline (not shown) may be attached to the slip assembly support structurey l5 so as to raise it clear of the obstruction while being moved to its out-onthe-wayv position.

The embodiment of the invention just described is universally adaptable to the various makes. and sizes of rotary machines because of the provision of the vertically adjustable stop bolts 82 and |21, these bolts making it possible to limit the stroke of the post l2 whereby thel slip assembly l5 will seat at exactly the correct depth Within the master bushing bowl il'. rlie guide means provided for the post f2 prevent wobble of the post with respect to the ira-me even at suchtime as said post reaches the top of its stroke. The mounting of the head member i3 for pivotal movement about the horizontal bolt irl! and pivotal movement about the vertical axis of the post |2 provides a simple arrangement for moving the slip assembly l5 and its support structure l5 into an inoperative storageA position Wholly clear of the rotary machine lli.

Having fully described my invention, it is to be understood that I do not wish to be limited to the details herein set forth, but my invention is of thev full scope of the appended claims,

I claim:

l. In a power unit for lifting a lateral support arm carrying a Well pipe slipassembly, the combination of: a stationary frame, an upright post, guide rollers carried on the upper portion of the frame engaging the post, a trunnion ring rotatably mounted on the lower end of the post and having laterally extending trunnions, rollers on the trunnions guided by vertical trackways on the frame, the upper end of the post extending above the frame, attachment parts on said upper end of they post for securing the lateral support arm thereto, and cooperating fluid operated elements for raising the post relative to the frame.

2. In a power unit' for lifting a lateral support arm carrying a well pipe slip assembly, the conibination of: a stationary frame, an upright post, guide rollers carried on the upper portion of the frame engaging the post, a trunnion ring rotatably mounted on the lower end of the post and having late-rally extending trunnions, rollers on the trunnions guided by vertical trackways on the frame, roles-sable latch parte for preventing relative rotation between the trunnion ring and the post, the upper end of the post extending above the frame, attachment parts on said upper end of the post for securing the lateral support arm thereto, and cooperating Huid-operated elements for raising the post relative to the frame.

3. In a power unit for lifting a lateral support arm carrying a well pipe slip assembly, 'the combination of: a stationary frame, an upright tabular' post, guide rollers carried on the upper portion of the yframe engaging the post, a trunnion ring rotatably mounted on the lower endof the post and having laterally extending trunlatch |00 adjacent the housing door |65, releasing 75 nions, rollers on the trunnions guided by vertical trackways on the frame, the upper end of the post extending above the frame, attachment parts on said upper end of the post for securing the lateral support arm thereto, an axially immovable piston rod turnably mounted on the base and extendinginto the interior of the post from the lower end thereof, a piston xed on the piston rod and slidably engaging the interior surlface of the tubular post to form a seal, the piston rod having` a conduit for admitting fluid pressure into the interior of the tubular post above the piston for raising the post relative to the frame. i

4. In a power unit for lifting a lateral support arm carrying a well pipe slip assembly, the combination of z a stationary frame, an upright tubular post, guide rollers carried on the upper portion of the frame engaging the post, a trunnion ring rotatably mounted on the lower end of 'the post and having laterally extending trunnions, cooperating latch parts for releasably latching the trunnion ring and post against relative rota tion, rollers on the trunnions guided by vertical trackways on the frame, the upper end of the post extending above the frame, attachment parts on said upper end of the post for securing the lateral support arm thereto, an axially immovable piston rod extending into the interior of the post from the lower end thereof, a thrust bearing rotatably supporting the piston rod upon the frame, and a piston iiXed on the piston rod and slidably engaging the interior surface of the tubular post to form a seal.

5. A power unit adapted to provide vertical reciprocal movement of a well pipe slip assembly support structure, comprising: a stationary frame, a post disposed within said frame for vertical re ciprocal movement with respect thereto, guide means disposed between said frame and said post to guide said post for vertical movement with respect to said frame, releasable latch means normally interlocking said frame and said post whereby said post is normally restrained against rotation with respect to said frame but is adaptable upon release of said latch means to be rotated about its vertical axis, a head member carried by said post and attachable to said slip assembly support structure, and horizontal pivot means mounting said head member on said post for pivotal swinging movement relative thereto.

6. A power unit adapted to provide vertical reciprocal movement of a well pipe slip assembly support structure, comprising: a stationary frame, a post disposed within said frame for vertical reciprocal movement with respect thereto, guide means disposed between said frame and said post to guide said post for vertical movement with respect to said frame, releasable latch means normally interlocking said frame and said post whereby said post is normally restrained against rotation with respect to said frame but is adaptable upon release of said latch means to be rotated about its Vertical axis, a head member carried by said post and attachable to said slip assembly support structure, horizontal pivot means mounting said head member on said post for pivotal swinging movement relative thereto, and means releasably latching said head member against pivotal swinging movement relative to said post.

7. In a power unit for lifting a well pipe slip assembly, the combination of: a stationary frame, a post guided for vertical movement on the frame, a platform member fixed on the upper end of the post, a tiltable member having a laterally extending support arm secured thereto, a horizontal pivot shaft pivotally connecting said members, releasable means for preventing relative pivotal movement between said members under normal operating conditions, said means including a frangible element proportioned to fail in the event that overload stresses should be applied to the support arm.

8. In a power unit for liftingl a well pipe slip assembly, the combination of: a stationary frame, a post guided for vertical movement on the frame, a platform member iiXed on the upper end of the post, a tiltable member having a laterally extending support arm secured thereto, a horizontal pivot shaft pivotally connecting said members, releasable means for preventing relative pivotal movement between said members under normal operating conditions, said means including Va link pivotally connected to each of said members at spaced locations, a portion of the link engaging one of the members so that relative pivotal movement between the members in one direction is prevented, and a latch on the other member releasably engaging the link so that relative pivotal movement between the members in the other direction is also prevented.

GIR/D E. MULLINIX.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,222,915 Anderson Apr. 17, 1917 1,784,553 Stukenburg Dec. 9, 1930 1,856,660 Schultz May 3, 1932 2,059,130 May Oct. 2.7, 1936 2,231,923 Koen Feb. 18, 1941 2,340,597 Kelley Feb. 1, 1944

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