CA1202998A - Shock absorbing snubber for derrick hooks - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An improved shock absorbing snubber for derrick hooks is shown which includes a stationary hydraulic plunger and a telescoping barrel arrangment. A spring loaded check valve mounted on the plunger allows generally free fluid flow as the barrel is moved in one direction relative to the plunger but restricts the flow of fluid as the barrel is moved in the opposite direction.

Description

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13ACKGI~OUND Ol` l`ill. INV~N1`1()N ~-This invention relates ~enerally to derrick hooks used on rotary earth drilling rigs and, more particularly, to an improved shock absorbing snubber of the type used to darllpen the vertical movement of the hook shank.
S Rotary earth drilling rigs used for drilling oil and L
gas wells utilize a traveling block and hook arrangement for tripping stands of pipe into and out of the well bore. When raising the pipe stand, an elevator assembly is positioned around the box end of the pipe held by slips in the ro~ary table. A pair of steel links connect the elevator assembly to the derrick hook. The derrick hook and associated trav- L
eling block are hoisted along tle vertical axis of the drilling rig by cable linkages.
Pipe strings at times extend tt)ous.1nds of feet into the earth requirin~ derrick hooks of massive size. I'rior ar~
hooks typically- have a shank which is free to move up and down withiln an outer housing. A helical coil spring is positioned~around the shank in the hook housing. A spring seat is connected to the upper el~d of the shank and engages the coil spring. Downward vertical movement of the shallk, 1.
such as occurs when a load is applied to the hook, compresses the spring.
In raising a stand of pipe from the well bore, the s1ips are relcased and the weight of the pipe string causes the hook shank to move downward alor-g Lhe vertical axis of the housing. This action compresses the coil spring positioned about the shank. When the pipe stand has been raised to the proper position, the slips are again engaged at the rotary and the pipe is unscrewed. As the threaded tool joint connection is unscrewed, the coil spring in the derrick hook exerts an upward force on the pipe stand. This upward force r assists in unscrewing the connection and in raising ~he stand of pipe high enough to allow it to be moved sidewise into the racking area.

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In order to prevent the pipe ~rom bouncing or "jumpin~ ;
out" as the sprin~ tension is relieved, a shock absorbin~
unit or "snubber" is utilized to dampen the ver~ical move-ment of the hook shank. By dampening the vertical travel oL
the shank, a controlled rate of return is achieved which prevents dama~e to the threaded tool joint connections.
In certain prior art embodimellt-s, the snubber unit is physically connected to the hook shank. One such snubber assembly uses a stationary plunger and a barrel that slides telescopingly over the plunger. The barrel is secured to the top of the shank. The plunger and barrel contain hydraulic fluid. An orifice in the bottom of the plunger restricts fluid flow between the barrel and plunger, dampening both upward and downward movement oE the shank. This design is dificult to service since it is necessary to disassemble the entire hook in order to service the snul)ber. A]so, application oE a sudden load to the hool( shank is Lrans~erre(l directly tq the snubber assembly SillCC ~he ~)arre1 i.s secured t.
to the top of the shank.
Other prior art snubbers are self-contair)ed units not r 20 physically connected to the hook shank. One such desi~n includes a piston located in a chamber in which hydraulic fluid exerts continuous hydrostatic pressure against the cylinder walls. The piston is biased downwardly and has a check valve that ~llows free fluid flow past the piston wi-en 25 moving downwardly. When moved upwardly, only restricted flow past the piston is allowed. Upward movemellt Or the shank pushes the piston upwardly, dampenin~ shank movemen~ only in the upward direction, as desired. The continuous pressure, however, in the chamber results in some leakage problems 30 around the piston sha~t, r . ~ _ .
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SUMMARY 0~ INVlNrl~N

It is accordingly an object Or this invention to b provide an improved snubber assembly which is easier ~o r maintain and has an improved service life.
Another object of this invention ;s to provide an i~lproved snubber assembly which is a seIf-contairled unit bul: L
which is not subjected to continuoui; fluid pressure in Lhe static state.
The i~nproved snubber of the present invention includes r a stationary hydraulic-plunger having a closed upper end mounted in the hook housing and cylindrical sidewalls. A
sliding barrel having a closed bottom and open top fits telescopingly over the plunger in concentric fashion. A
check valve including a spring biased plate is mounted on the lower end of the plunger. The check valve allows generally free flow of fluid when the barrel moves downward relative to the plunger, but restricts fluid flow upon upward move-ment of t~e barrel. The barrel is urged downwardly by a .
spring. U~warcl travel of the shank forces the barrel up- r:~
wardly, resultillg in dampening.

r BRIEF DESCRIPTION OI TIIE ~I~AWlN(,S

Fig. 1 is a partially sectioned side view o a d~errick hook constructed in accordance with this invention.
Fig. 2 is an enlarged view of the upper portion oE the derrick hook of Fig. 1I partially in section.
Fig. 3 is a sectional enlarged view of a portion oE the derrick hook of Fig. 1, illustrating the operation of the snubber as a load is applied to the hook shank.
Fig. 4 is a sectional enlarged view of a portion of the derrick hook of Fig. 1, similar to Fig. 3 and showing the operation of the snubber as load is removed from the hook shank.
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DETAlL~D D~SCRIPrLON ()L [ll~ lNV~NII()~

Referring no-~ to Fig. 1, there is shown a derrickllook designated generally as 11. Verrick hook 11 includes a hook body 13 which engages the elevator-link assemb~y (notshown) used to raise and lower pipe ;nto and out of the well bore.
A bail 15 is provided on the upper end of hook 11 ~or connection to the derrick traveling block. A shank 17 is r connected to the hook body 13 by means of a pin 19. Shank 17 is rnounted with'ih a hook housing 21 for movement along and rotation about the vertical axis thereof. Shank 17 is lû polygonal in cross section and has an upper Elanged end 23, an intermediate region 25, and lower end 27.
A swivel ring 29 having a flared upper end 31, a transverse upper surface 33 and generally cylindrical lo~ler section 35, is mounted coaxially with Lhe shank l7 in the hook housing 21. Swivel ring 33 has a polygonal opening 37 adapted to receive the intermediate region 25 of shank l7, so that rotation of the shank 17 causes corres~)on~ing rotation o~ the swivel ring 29. Fl.ared upper end 31 ofswivel ring 29 rides on a bearing unit including upper race 39, lower race 41, and plurality of balls 43. Lower race 41 is received by circurnferential ledge 45 in housing 21.
An annular spring guide 47 rests on the upper trans-verse surEace 33 of swivel ring 29.The internal dia~neter of spring guide 47 is selected to allow the upper Elanged end 23 oE shank 17 to slide inside the spring guide 47 as shank 17 moves along the vertical axis of the hook housing 21.
An annular spring seat 49 having a bott:om end 51 and flared end 53 is connected to the upper Elan~ed end 23 of shank 17 by a plurality of balls 55 in a common race. The flared end 53 oE spring seat49 engages a helical coil spring 57 positioned about shank 17 in hook housing 21, so that downward vertical movement of the shank 19 coml)resses the i' ,, ,,,,, , " ........ . .. --spring 57. The axial spring force exerte~ by s~)r;og 57 on spring guide 47 maintains the position Or spring guide 47 on swivel ring 29. r The snubber assembly denoted generally as 59 in Fig. 1 is shown in greater detail in F`ig. 2. Snubber assembly 59 includes a stationary hydraulic plull~er 61 havirlg a closed mounting end 63, cylindrical sidewalls 65 and a lower etld 67. Mounting end 63 includes a lip 69 which is secured to hook housing 21 as by bolts 71. Mounting end 63 of plunger 61 is sealed by means of a cover 73 and bolts 75. A fill port 77 is provided with a lock screw. Low pressure spring loaded exha--st valves 79, 81 are positioned in mounting end 63 for serving as air passage means to allow flir displacement. The lower end 67 of plunger 61 is provided with a plurality of orifices 83 to allow 1uid flow into and out o~ the interior of plunger 61.
A sliding barrel 85 having a closed bottom 87 of resilient material, cylindrical sidewalls 89 and an open top-91 is adapted to receive the lower elld 67 of plunger 61 in telescopingly, concentric fashion. rhe internal diameter of barrel 85 is selected to allow the inner sidewalls of barrel 85 to slidingly engage the external sidewalls of plunger 61.
The lower end 67 serves as a partition dividing the in-terio~s of the plunger 61 and barrel 85 into a lower cl-am~er and an upward chamber. A helical coil spring 93 is positioned about snubber assembly 59 with one end seated about the closed bottom 87 of barrel 85 and the opposite end seated against the underside of lip 69 of hydraulic plunger 61. Thus in the position shown in Fig. 2, spring 93 exerts a downward force on barrel 85 causing the lower end 87 to contact upper flanged end 23 of shank 17.
In order to assure a tight fluid seal, the open end 91 of barrel 85 is provided with an annular soft metal wear bushing 95 having a groove 97 cut to receive a urethane rod wiper. A retainer plate 99 fastens busl-ing 95 to the openc~nd - u -91 of barrel 85 as by bolts 101. The lower end 87 oE barrel 85 has an o -ring seal 103 at the interrace or the lower end 87 with the sidewalls 89 to contain fluid in the interior oE r the barrel. Vent holes 105 are drilled in the siclewalls 89 5to allow air displacement in an annular space 107 between the barrel 85 and plunger 61.
A check valve 10~ is provided on the lower end 67 of plunger 61. Referring to Figs. 3 atld 4 check valve 109 r includes a spring biased plate 111 moveable between a seated r 10position to restrict fluid flow and an unseated position for greater relative fluid flow. Sprin~ biased plate 111 is circular in shape and has a plurality of holes 113 each hole 113 in approximate vertical alignment with one oE the orifices 83 in the lower end 67 of plunger 61. rhe diameter 15of orifices 83 is at least twice the diameter of ma-ing holes r 113, thus the total cross-sectional area of the orifices 83 is greater than the total cross-sectional area oÇ ho]es 113.
In addition, a circumferential grove ~0 cut in the exterior surface of lower end 67 connects the oriEices 83 to provide 20for fluid flow in the event that holes 113 in plate l11 are not in perEect alignment with the orifice.s ~3 in plunger 61.
Plate 111 and lower end 67 are drilled to receive a bolt or shaft 119 which is held in place by washer ll7 and n~Jt 121.
A compression spring 115 seats at one end against the 25interior of lower end 67 and at the opposite end against washer 117. The exterior surface oE lower end 67 has a recess 123 oE slightly larger internal diameter than the external diameter Or plate 111 when plate 111 is seated.
Circumferential grooves 125 and 127 are cut itl the 30exterior sidewalls of lower end 67. Groove 125 contains a packing seal to prevent fluid loss. Groove 127 is Litted with a wear ring to lessen metal to meta1 contact between the sidewalls of the plunger and barrel. In the preferrcd embodiment, the external diameter of plunger 61 decreases 35gradually from the mounting end 63 to ti-e lower end 67 whilc the internal diameter of the barrel ~5 ~,radually dclcreases from the open top ~1 to the closed bottom 87 In this manner, the packing grove 125 will easily pass within the bushing 95 r of barrel 85 to facilitate assembly or disassembly of Lhc unit The operation of the improved snubber can best be understood by reference to Fig 's 3 and 4 ln Fig 3, the snubber unit has been filled ap~roximately half full with substantially incompressible hydraulic fluid 129 throu~h fill port 77 The hydraulic fluid volume should be less than the total volume of the plunger 61 and barrel ~5 when the barrel is in its uppermost position ~s a load is applied to shank 17, the shank begins to move vercicallly downward in housing 21. As upper end 23 of shank 17 moves downward, spring 93 forces barrel 85 to slide down stationary plunger 61 As barrel 85 moves downward, a partial VclCUUm i.S created in l-1er chamber 131. Hydraulic fluid flows From upper chamber 133 into lower chamber 131 to Fill the increased volume ~luid flows downward throu~h orifices ~3 an~ holes 113 Fluid pressure overcomes the resistance Or spring 115, thereby unseating plate 11l and allowing generally free flow of fluid around plate 111 and into the lower chamber 131 In Fig 4, the load has been removed from hook shank 17 causing it to spring upward and contact closed bottom 87 oF
barrel 85 As the closed bottom 87 is driven upward, the volume of hydraulic fluid in lower chamber 131 is COln pressed, forcing fluid against plate 111 and ~seatirlg p]ate lll in recess 123 in the lower end of l)lun~er 61 I`he only available 1uid passageway is through the relatively s~nall diameter holes 113 in plate 111, restrictin~ Fluid Flow back int,~ upper chamber 133 By restricl-ing the upward travel of t-the hook shank, a controlled rate of return is achieved The internal diameter of the holes 113 carll)e varied to vary the rate of return of the barre~ relative to the plunger Preferably the internal diameter of ~he holes 113 is se- ) lected so tl~at Lhe internal diameter Or Lhe oriLiccs ~3 are at least twice as great as the hole diameters aL i:he point at which plate 111 contacts plunger 61. Since there is insuLficient fluid to fill both the lower chamber 131 and upper chamber 133, upper chamber 133 will always be only partially ull. Lower chamber 13l wi]l be always full excepc for the momentary drawing o~ vacuum whe[l the barre] 85 s~arts downward. The upper chamber 133 is of fixed volume and the lower chamber 131 varies in volume with barrel 85 movement. r Air moves in and out of ports 79, 81 in upper chamber 133 in response to hydraulic fluid volume changes in the upper chamber, and to keep the upper chamber pressure substan-tially ambient.
It should be apparent from the foregoing that arl ~
invention has been provided with significant advantages. r The improved snubber assembly is subjected to Elllid pressure only in the dynamic state when the hook shank is moving vertic~lly~upward and exerting a rorce on the barrel. As a result, th~re is less chance of seal leakc-l~e and the ne~d Eor frequent maintenance than in a snubber having ~luid pressure in a static condition. The improv.ed snubber allows rela- r tively free movement of the barrel downward with respect to ' the plunger, and restricts only the return movement. The snubber assembly is a self contained uniL which can be removed to be serviced without disassemblin~ the hook. Since the snubber is not physically connected to the shank, a sudden load applied to the shank does not place undue stress on the snubber.
While the invention has been shown in only one of its forms, it should be apparent Lo those skilled in the art that it is not so limited but is susceptible to various changes and modifications without departing Erom the spirit ti-ere-o~ .

Claims (2)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A shock absorbing snubber for a derrick hook of the type having a housing, a shank axially movable in the housing, and a load bearing hook connected to the lower end of the shank, comprising:
a plunger carried by the housing, having a hollow interior and a lower end;
a sliding barrel having a closed bottom adapted to be contacted by the upper end of the shank, and an open top telescopingly receiving the lower end of the plunger;
the barrel and plunger containing hydraulic fluid with a volume less than the volume of the interiors of the barrel and the plunger when the shank has pushed the barrel to an uppermost position;
check valve means mounted in the interior of the plunger for restricting fluid flow rate from the barrel to the plunger upon movement of the barrel upward relative to the plunger, and for allowing an increased rate of fluid flow from the plunger to the barrel upon movement of the barrel downward relative to the plunger; and air passage means in the top of the plunger communicating with the atmosphere for allowing air to pass in and out of the plunger above the hydraulic fluid in response to hydraulic fluid volume changes to maintain the pressure in the plunger substantially at ambient.

2. A shock absorbing snubber for a derrick hook of the type having a housing, a shank axially movable in the housing, and a load bearing hook connected to the lower end of the shank, comprising:
a plunger carried by the housing, having a hollow interior and a lower end;
a sliding barrel having a closed bottom adapted to be contacted by the upper end of the shank, and an open top telescopingly receiving the lower end of the plunger;

the barrel and plunger containing hydraulic fluid with a volume less than the volume of the interiors of the barrel and the plunger when the shank has pushed the barrel to an uppermost position;
check valve means mounted in the plunger for allowing generally free flow of fluid from the plunger to the barrel when the barrel moves downwardly, and restricting the flow of fluid from the barrel to the plunger when the barrel is pushed upwardly by the shank; and low pressure spring loaded exhaust valves in the top of the plunger communicating with the atmosphere for allowing air to pass in and out of the plunger above the hydraulic fluid in response to hydraulic fluid volume changes to maintain the pressure in the plunger substantially at ambient.