CA1138490A - Rotary shouldered connection modification - Google Patents
Rotary shouldered connection modificationInfo
- Publication number
- CA1138490A CA1138490A CA000359338A CA359338A CA1138490A CA 1138490 A CA1138490 A CA 1138490A CA 000359338 A CA000359338 A CA 000359338A CA 359338 A CA359338 A CA 359338A CA 1138490 A CA1138490 A CA 1138490A
- Authority
- CA
- Canada
- Prior art keywords
- pin
- box
- threads
- sleeve
- threaded portion
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
Abstract A rotary shouldered pin and box connection in an earth boring drill string is modified by eliminating some threads of the box to form a cylindrical portion and similarly cutting away some threads on the outer end of a pin to form a cylindrical portion. A sleeve is positioned in the box cylindrical portion to receive the pin end, with the result that bending forces are transmitted through the sleeve rather than through the threaded connection.
Description
i-1.' ~ ROTARY S~OULDERED CONNECTION r~ODIFICATION
! Field of the Invention Tnis invention relates to earth boring operations and particularly to an improved connection between two components of a drill string.
Background of the Invention One very common means of joining two components of a drill string in an earth boring operation is a rotar~
shouldered connection, which is also often called a pin and box joint. In one example of this a drill stem i attached to a drill bit is formed with threads on the ; exterior of its upper end to become the pin. The threads are typically tapered so that the thread at the axially outer or upper end has a smaller diameter than the thread at the lower or axially inner end of the threaded portion. Adjacent the largest thread is an outwardly extending shoulder facing axially towards the threaded end.
A stabilizer, drill collar or other component to be attached to the pin is formed with an interiorily threaded end portion, commonly referred to as the box.
The box thread on the open axially outer end tapers axially to a diameter of smaller cross section on the axially inner end to mate properly with the threads on the pin. The tapered arrangement permits the pin to be inserted a considerable distance into the box be~ore it is necessary to rotate one or the other components to engage the threads. Also, with the tapered arrangement, the components are completely threadably engaged with a small amount of relative rotation, thus simplifying the threading operation, which is very convenient for components which are typically very heavy.
The threads are located and constructed such that the outer axial face of the box engages the shoulder on the pin when the threads are completely engaged. These axial faces are very accurately formed to form a seal 1138~90
! Field of the Invention Tnis invention relates to earth boring operations and particularly to an improved connection between two components of a drill string.
Background of the Invention One very common means of joining two components of a drill string in an earth boring operation is a rotar~
shouldered connection, which is also often called a pin and box joint. In one example of this a drill stem i attached to a drill bit is formed with threads on the ; exterior of its upper end to become the pin. The threads are typically tapered so that the thread at the axially outer or upper end has a smaller diameter than the thread at the lower or axially inner end of the threaded portion. Adjacent the largest thread is an outwardly extending shoulder facing axially towards the threaded end.
A stabilizer, drill collar or other component to be attached to the pin is formed with an interiorily threaded end portion, commonly referred to as the box.
The box thread on the open axially outer end tapers axially to a diameter of smaller cross section on the axially inner end to mate properly with the threads on the pin. The tapered arrangement permits the pin to be inserted a considerable distance into the box be~ore it is necessary to rotate one or the other components to engage the threads. Also, with the tapered arrangement, the components are completely threadably engaged with a small amount of relative rotation, thus simplifying the threading operation, which is very convenient for components which are typically very heavy.
The threads are located and constructed such that the outer axial face of the box engages the shoulder on the pin when the threads are completely engaged. These axial faces are very accurately formed to form a seal 1138~90
- 2 -for the joint so that drilling fluid cannot leak between the tubular drill string members and the annular space between the drill string and the surrounding drill hole.
In a drilling operation, the drill string components receive lateral or bending forces as well as axial I compressiv2 and tensile forces. These lateral or bending ¦ forces are particularly troublesome with respect to pin and box joints in that repeated forces of this nature repeatedly stress the metal and can eventually cause failure.
During this bending action the sides of the threaded connection are alternately placed in compres5ion and tension forces. This is somewhat analogous to the forces occuring in a piece of wire when it is bent back and forth alony its axis. After repeated bending a wire will break, and it will break more quickly at a change of diameter, a notch or weak point in it.
Similarly, the roots of a thread in a threaded joint represent notches or weak points at which failure can occur. This is particularly true when the components joined are thicker or of larger diameter than the pin and box, such as ~hen a drill collar or a stabilizer is connected to a drill stem. These ~atçral bending ~P
forc~s add to the tensile forces;are particularly large with heavy components, such as a la~ge diameter raise head drill bit. Consequently, failure of the pin and box joint between the drill stem of a raise head drill bit assembly and a component connected to the - 30 drill stem is a particular problem.
In analyzing such failures it has b2en found that a very high percentage of them occur in the box at a position adjacent to the end thread of the pin. ~hat is, the failure is near the inner end of the box threaded portion. It is believed that the end thread on the pin creates a "notch" effect on the adjacent ~13~
box structure with the stem under tension. When a bending force is applied it produces additional tension -forces on one side of the ioint. Further, this bending load urges the axis of the pin out of line with the axis of the box which in turn increases tensile loads on the thread on the side away from the center of ~; ' curvature of the bend. Such loads are especially detrimental at the last engaged thread. With the pin ~' 10 axis being moved off center with respect to the axial bore, the side load to the thread tends to cause the thread to act like a wedge producing additional local stresses in the box thread, which are in the same -direction as, and additional to the tensile loads.
Summary of the Inven'tion As a means to minimize such failures in the pin and box joints, the outer end of the pin is formed'with a cylindrical portion and the inner end of the box is formed with a similar cylindrical portion so that lateral forces may be transmitted through these cylindrical portions rather than through the threads which would normally be in this area. This relieves or distributes the forces which are concentrated in a particular thread root so that the forces are - 25 transmitted to a larger area thus reducing failures.
- By properly selecting the diameters of the cylindrical portions a sleeve ~ay be positioned between the cylindrical portions. That is, the outer surface of the sleeve snugly engages the surrounding cylindrical surface in the box and the cylindrical surface on the pin is inserted into and snugly engages the inner ' surface of the sleeve.
Existing pin and box threads may be modified by forming the cylindrical portions. With this modification an unmodified pin can still be used with a modified box; and conversely, an unmodified box may be used with a modified pin.
113~490 Description of the Drawings Fig. 1 is a schematic view of a drill string carrying a raise head drill bit and illustrating the location of a pin and box connection that is subjected to high tensile and bending forces;
Fig. la is a schematic view of a drill string illustrating lateral bending forces;
Fig. 2 is a cross-sectional view of a modified pin and box connection employing a sleeve to transmit benaing forces;
Fig. 3 is a cross-sectional view showing a regular or unmodified pin with a modified box and with the ' sleeve removed;
,~', 15 ~ig. 4 is a cross-sectional view of a modified pin insertea in a regular box;
Fig. 5 is an enlarged view of a commonly used pin and box thread in which lateral or bending forces are particular problem;
Fig. 6 is an alternative form of the invention employing a cylindrical surface on both sides of a - threaded section.
Referring first to Fig. 1 there is schematically - illustrated a dril-ling assembly lO, often referred to '25 as a raise head, having a plurality of cutters 12 on its upper surface for cutting a large-hole as the '' assembly is'rotated and pulled upwardly. The asse~bly includes a-stem 1~ which extends upwardly through a , pilot hole 16, and is connected to a stabilizer, drill collar or other component 18 in a drill string leading to the drill rig (not shown). The invention concerns ' the joint or connection bet,ween the cutter assemhly stem 14 and the member 18, or other such joints within a drill string.
As mentioned above, the connections between drill string components receive lateral or bending forces in addition to vertical loads., While the axial loads in a vertical hole in a raise drilling opera-tion are ~138490 much larger than the transverse forces, the magnitude o the transverse forces nevertheless produce very - significant stresses on the connections. Such loads are of course increased with slant or non-vertical holes. Figure la illustrates this in a very exaggerated manner wherein a drill string 21 is shown in a wavey or bent configuration, with the string being bent around large radius centers of curvature. ~hus, a~
the instant shown for the connection 23,structure on the inner side of the bending curve is in compression while the structure on the outer side of the bending - curve is in tension due to these lateral forces. The invention is directed to an improved structure for accommodating such bending forces and other forces on the connection.
Fig. 2 is an enlarged cross-sectional view of such a connection. As can be seen, both members 14 and 18 are tubuIar and are joined by a pin and box threaded connection. The end 15 of member 14, which is often referred to as the pin, has an exterior diameter which is smaller than that of the main body of the member 14. It includes a threaded portion 20 on its exterior surface which tapers in diameter becoming smaller in the direction towards the end of the pin 15.
An unthread~d relief area 22 is loGated ad3acent the inner, or large diameter end 2Oa of the tapered thread 20. An annular shoulder 24 having an axial face facing - the end of the pin extends radially outwardly from the unthreaded portion 22 and larger end of the threaded portion 20.
The member 18 includes an inner threaded portion-26 on its lower open end 19. This interiorily threaded end portion 19 mates with the pin threads 20 and is commonly referred to as a box. The threaded portion 26 tapers from the thread 26a at the outer end of the box decreasing in diameter towards the axially inner end 113~3490 26b. In otherwords, the taper is opposite to that of the pin so that the pin and box threads mate properly.
As is well-known, the purpose for the tapered threads is to permit the pin to be inserted a considerable distance into the box before the threads engage and the threads can then become completely engaged with a small amount of relative rotation between the members. This is of great importance due to the mass of man~ of the components being joined and due to the fact that drill stem members have to be repeatedly connected and unconnected as the drilling depth changes and access to the drill bit is required.
The pin and box are designed so that the pin shoulder 24 and the box end face 28 are tightly engaged when the threaded connection has been fully made; and thes~
mating surfaces are accurately machined so that a fluid tight seal is formed. This of course is re~uired to prevent fluid communication between the interior passage 29 and the annular space 16 surrounding the drill stem. These mating surfaces also accommodate compressive forces.
In the prior art pin and box connections, the tapered threads 20 extend to the end of the pin, and the tapered threads 26 extend inwardly within the box as far as necessary to accommodate the threads of the pin. Such reguiar pin is shown at 44 in Fig. 3; and a -regular box is shown at 48 in Figure 4. As discussed - above, most failures have occurrea in the box in the area of the inner end 26b or of the box thread adjacen-t the pin end. This stress concentration area is roughly indicated by the numeral 30 in Fig. 2.
To minimize the nu~ber of failures in this area, the threads on the inner end of the box have been eliminated. In the case of modifying an existing box the threads are ~ut away by boring or drilling to form a substantially unthreade~ cylindrical inner wall or t 5P
1~38490 surface 32 at the inner end of the box~ As can be seen from Fig. 2, this cylindrical surface extends from an inner shoulder 34 to the inner end of the box to a point nearly half way to the end of the outer end of the box. Also, the threads on the outer end of the pin are cut away to form a cylindrical surface 36 which extends from the outer end of the pin nearly half T~ay to the end of the threaded portion 20. ~s can be seen the diameter of the cylindrical surface 32 is smaller than the crest o the adjacent thread 26 and the diameter of the cylindrical pin surface 36 is smaller than the remaining thread 20. Further, the diameter of the surface 36 is smaller than the diameter of the surface 34. A cylindrical sleeve 40 is press fit into the cylindrical surface 32 in the box and the pin end is inserted more than half way into the sleeve, with the sleeve inner surface snugly engaging the outer cylindrical surface 36 on the pin.
With this arrangement, lateral or bending forces are transmitted between the pin and the box primarily through the sleeve 40 rather than through the threads.-Thus, the forces are distributed a significant distance - ' -- along the pin and box rather than through concentrated stress areas as existed without the sleeve approach.
Conseguently-, the threads are primarily sub3ected to axial forces in conjunction with the interface between the end face 28 and the shoulder 24. This in turn minimizes or eliminates the need for the threads to be quite so precise from a lateral or transverse standpoint.
Another advantage of the modification is that the regular or unmodiied pin 44 as seen in Fig. 3 can be used with a modified box 19~ That is, the substantially unthreaaed cylindrical recess 32 is formed in the box but no sleeve is positioned therein.
Conversely, as seen in Fig. 4, a modified pin 15 may be utilized with an unmodified box 48, although there ~13~490 is less support for lateral forces than with a totall~
unmodified arrangement. That is, the pin is formed with the c~lindrical surface 36 but it does not cooperate or interfere with the ad~acent threads 26b on the box 48.
The threads shown in Figs. 2 - 4 are intended to indicaLe generally any thread form. Figure 5 illustrates a specific thread form commonly used for rotary shouldered connections rece~iving tremendously high loaas.
It is a thread which is frequently used when the joint is subjected to high tensile stresses such as in a raise boring operation, as illustrated in Fig. 1. Such thread is identified as DI-22 by Drillco Industrial, a division of Smith ~nternational, Inc., assignee of the present invention. The thread is relatively deep and coarse with the thread angle being about 45 degrees on the flank 50 with respect to a radial plane or line perpendicular to the drill pin axis 52, and only about 15 degrees on the pressure flank 54, as is illustrated in Fig. 5. The high angle, non-pressure flank 50 facilitates insertion of the pin into the box. The low -angle, pressure flank 54 minimizes outward or "hoop"
stresses on the surrounding box during non bending, concentric operation. The thread has a relativel~ low taper angle, and it has a relatively low "break out", ~ or uncoupling force to "make up" or coupling torque ratio.
Analysis of failures of box threads for eight and a quarter inch diameter connections employing the thread of the type illustrated in Fig. 5 indicates that, in raised drilling Dperations as shown in Fig. 1, approxima~ely 90 percent of the failures caused by fatigue of the box of the member 18 where connected to the stem 14 occur in the area indicated b~ the numeral 30 in Fig. 2. The metal fatigue failure is thought to occur for a variety of reasons. The threads are under large tensile forces. The last thread on the end 1131~49~
of the pin produces a "no-tch" e~ect in the surrounding box strucLure, when a tensile load is applied to the joint. By way of illustration in Fig. 5, this would be in the area 30 adjacent the pin thread 20b. Bending ^ loads applied to the connection, force the axis 52 ' (Fig. 2) of the pin out of alignment with the a-~is of the box, (not separately shown) which increases tensile loads on the thread on the side of the thread remote from the center of bending curvature. Assume for analysis purposes, that the center of bending is to the left of the paper in Fig. 5, such as it would be for the connection 23 when illustrated as in Fig. la.
Such loads are especially detrimental at the area 30 due to the notch effect mentioned above. Such loads move the small end of the pin slightly off center with respect to the axis of the bore imparting a severe side load to the thread which causes the thread flank ¦~ 54 to tend to act like a wedge producing local stresses in the surrounding box thread which are in the same direction as the additional stress aue to the tensile loads. This wedging effect is particularl~ severe ` with the shallow l5 degree pressure flan~ thread illustrated in Fig. 5.
The sleeve design of Fig. 2 effectively prevents the small end of the pin from moving off center with -respect to the box and eliminates the wedging efect on the threads which are not centralized. Further, the sleeve design is intended to enable the threaded - 30 section to provide a better resistance to tensile loads, free of any requirements to provide centralizing of the connection. The sleeve provides a direct path for the transmission of loads perpendicular to the axis of the connection from the pin to the box and vice versa. Thus, the sleeve provides a simple but effective solution to a troublesome and costly problem.
Fig. 6 is a somewhat schematic view of an : . - - , ... .
alterna-tive form of the invention wherein a pin 60 and a box 62 are provided with cylindrical portions 64 and 66 on opposite ends of a threaded portion 68.
The cylindrical portions may mate directly with each o-ther as shown or may be formed to receive sleeves along the lines shown in Fig. 2. In either case, lateral.forces are accommodated by the cylindrical portions and thus minimize such forces on the thread area to reduce failures in pin and box connections, .
.
,
In a drilling operation, the drill string components receive lateral or bending forces as well as axial I compressiv2 and tensile forces. These lateral or bending ¦ forces are particularly troublesome with respect to pin and box joints in that repeated forces of this nature repeatedly stress the metal and can eventually cause failure.
During this bending action the sides of the threaded connection are alternately placed in compres5ion and tension forces. This is somewhat analogous to the forces occuring in a piece of wire when it is bent back and forth alony its axis. After repeated bending a wire will break, and it will break more quickly at a change of diameter, a notch or weak point in it.
Similarly, the roots of a thread in a threaded joint represent notches or weak points at which failure can occur. This is particularly true when the components joined are thicker or of larger diameter than the pin and box, such as ~hen a drill collar or a stabilizer is connected to a drill stem. These ~atçral bending ~P
forc~s add to the tensile forces;are particularly large with heavy components, such as a la~ge diameter raise head drill bit. Consequently, failure of the pin and box joint between the drill stem of a raise head drill bit assembly and a component connected to the - 30 drill stem is a particular problem.
In analyzing such failures it has b2en found that a very high percentage of them occur in the box at a position adjacent to the end thread of the pin. ~hat is, the failure is near the inner end of the box threaded portion. It is believed that the end thread on the pin creates a "notch" effect on the adjacent ~13~
box structure with the stem under tension. When a bending force is applied it produces additional tension -forces on one side of the ioint. Further, this bending load urges the axis of the pin out of line with the axis of the box which in turn increases tensile loads on the thread on the side away from the center of ~; ' curvature of the bend. Such loads are especially detrimental at the last engaged thread. With the pin ~' 10 axis being moved off center with respect to the axial bore, the side load to the thread tends to cause the thread to act like a wedge producing additional local stresses in the box thread, which are in the same -direction as, and additional to the tensile loads.
Summary of the Inven'tion As a means to minimize such failures in the pin and box joints, the outer end of the pin is formed'with a cylindrical portion and the inner end of the box is formed with a similar cylindrical portion so that lateral forces may be transmitted through these cylindrical portions rather than through the threads which would normally be in this area. This relieves or distributes the forces which are concentrated in a particular thread root so that the forces are - 25 transmitted to a larger area thus reducing failures.
- By properly selecting the diameters of the cylindrical portions a sleeve ~ay be positioned between the cylindrical portions. That is, the outer surface of the sleeve snugly engages the surrounding cylindrical surface in the box and the cylindrical surface on the pin is inserted into and snugly engages the inner ' surface of the sleeve.
Existing pin and box threads may be modified by forming the cylindrical portions. With this modification an unmodified pin can still be used with a modified box; and conversely, an unmodified box may be used with a modified pin.
113~490 Description of the Drawings Fig. 1 is a schematic view of a drill string carrying a raise head drill bit and illustrating the location of a pin and box connection that is subjected to high tensile and bending forces;
Fig. la is a schematic view of a drill string illustrating lateral bending forces;
Fig. 2 is a cross-sectional view of a modified pin and box connection employing a sleeve to transmit benaing forces;
Fig. 3 is a cross-sectional view showing a regular or unmodified pin with a modified box and with the ' sleeve removed;
,~', 15 ~ig. 4 is a cross-sectional view of a modified pin insertea in a regular box;
Fig. 5 is an enlarged view of a commonly used pin and box thread in which lateral or bending forces are particular problem;
Fig. 6 is an alternative form of the invention employing a cylindrical surface on both sides of a - threaded section.
Referring first to Fig. 1 there is schematically - illustrated a dril-ling assembly lO, often referred to '25 as a raise head, having a plurality of cutters 12 on its upper surface for cutting a large-hole as the '' assembly is'rotated and pulled upwardly. The asse~bly includes a-stem 1~ which extends upwardly through a , pilot hole 16, and is connected to a stabilizer, drill collar or other component 18 in a drill string leading to the drill rig (not shown). The invention concerns ' the joint or connection bet,ween the cutter assemhly stem 14 and the member 18, or other such joints within a drill string.
As mentioned above, the connections between drill string components receive lateral or bending forces in addition to vertical loads., While the axial loads in a vertical hole in a raise drilling opera-tion are ~138490 much larger than the transverse forces, the magnitude o the transverse forces nevertheless produce very - significant stresses on the connections. Such loads are of course increased with slant or non-vertical holes. Figure la illustrates this in a very exaggerated manner wherein a drill string 21 is shown in a wavey or bent configuration, with the string being bent around large radius centers of curvature. ~hus, a~
the instant shown for the connection 23,structure on the inner side of the bending curve is in compression while the structure on the outer side of the bending - curve is in tension due to these lateral forces. The invention is directed to an improved structure for accommodating such bending forces and other forces on the connection.
Fig. 2 is an enlarged cross-sectional view of such a connection. As can be seen, both members 14 and 18 are tubuIar and are joined by a pin and box threaded connection. The end 15 of member 14, which is often referred to as the pin, has an exterior diameter which is smaller than that of the main body of the member 14. It includes a threaded portion 20 on its exterior surface which tapers in diameter becoming smaller in the direction towards the end of the pin 15.
An unthread~d relief area 22 is loGated ad3acent the inner, or large diameter end 2Oa of the tapered thread 20. An annular shoulder 24 having an axial face facing - the end of the pin extends radially outwardly from the unthreaded portion 22 and larger end of the threaded portion 20.
The member 18 includes an inner threaded portion-26 on its lower open end 19. This interiorily threaded end portion 19 mates with the pin threads 20 and is commonly referred to as a box. The threaded portion 26 tapers from the thread 26a at the outer end of the box decreasing in diameter towards the axially inner end 113~3490 26b. In otherwords, the taper is opposite to that of the pin so that the pin and box threads mate properly.
As is well-known, the purpose for the tapered threads is to permit the pin to be inserted a considerable distance into the box before the threads engage and the threads can then become completely engaged with a small amount of relative rotation between the members. This is of great importance due to the mass of man~ of the components being joined and due to the fact that drill stem members have to be repeatedly connected and unconnected as the drilling depth changes and access to the drill bit is required.
The pin and box are designed so that the pin shoulder 24 and the box end face 28 are tightly engaged when the threaded connection has been fully made; and thes~
mating surfaces are accurately machined so that a fluid tight seal is formed. This of course is re~uired to prevent fluid communication between the interior passage 29 and the annular space 16 surrounding the drill stem. These mating surfaces also accommodate compressive forces.
In the prior art pin and box connections, the tapered threads 20 extend to the end of the pin, and the tapered threads 26 extend inwardly within the box as far as necessary to accommodate the threads of the pin. Such reguiar pin is shown at 44 in Fig. 3; and a -regular box is shown at 48 in Figure 4. As discussed - above, most failures have occurrea in the box in the area of the inner end 26b or of the box thread adjacen-t the pin end. This stress concentration area is roughly indicated by the numeral 30 in Fig. 2.
To minimize the nu~ber of failures in this area, the threads on the inner end of the box have been eliminated. In the case of modifying an existing box the threads are ~ut away by boring or drilling to form a substantially unthreade~ cylindrical inner wall or t 5P
1~38490 surface 32 at the inner end of the box~ As can be seen from Fig. 2, this cylindrical surface extends from an inner shoulder 34 to the inner end of the box to a point nearly half way to the end of the outer end of the box. Also, the threads on the outer end of the pin are cut away to form a cylindrical surface 36 which extends from the outer end of the pin nearly half T~ay to the end of the threaded portion 20. ~s can be seen the diameter of the cylindrical surface 32 is smaller than the crest o the adjacent thread 26 and the diameter of the cylindrical pin surface 36 is smaller than the remaining thread 20. Further, the diameter of the surface 36 is smaller than the diameter of the surface 34. A cylindrical sleeve 40 is press fit into the cylindrical surface 32 in the box and the pin end is inserted more than half way into the sleeve, with the sleeve inner surface snugly engaging the outer cylindrical surface 36 on the pin.
With this arrangement, lateral or bending forces are transmitted between the pin and the box primarily through the sleeve 40 rather than through the threads.-Thus, the forces are distributed a significant distance - ' -- along the pin and box rather than through concentrated stress areas as existed without the sleeve approach.
Conseguently-, the threads are primarily sub3ected to axial forces in conjunction with the interface between the end face 28 and the shoulder 24. This in turn minimizes or eliminates the need for the threads to be quite so precise from a lateral or transverse standpoint.
Another advantage of the modification is that the regular or unmodiied pin 44 as seen in Fig. 3 can be used with a modified box 19~ That is, the substantially unthreaaed cylindrical recess 32 is formed in the box but no sleeve is positioned therein.
Conversely, as seen in Fig. 4, a modified pin 15 may be utilized with an unmodified box 48, although there ~13~490 is less support for lateral forces than with a totall~
unmodified arrangement. That is, the pin is formed with the c~lindrical surface 36 but it does not cooperate or interfere with the ad~acent threads 26b on the box 48.
The threads shown in Figs. 2 - 4 are intended to indicaLe generally any thread form. Figure 5 illustrates a specific thread form commonly used for rotary shouldered connections rece~iving tremendously high loaas.
It is a thread which is frequently used when the joint is subjected to high tensile stresses such as in a raise boring operation, as illustrated in Fig. 1. Such thread is identified as DI-22 by Drillco Industrial, a division of Smith ~nternational, Inc., assignee of the present invention. The thread is relatively deep and coarse with the thread angle being about 45 degrees on the flank 50 with respect to a radial plane or line perpendicular to the drill pin axis 52, and only about 15 degrees on the pressure flank 54, as is illustrated in Fig. 5. The high angle, non-pressure flank 50 facilitates insertion of the pin into the box. The low -angle, pressure flank 54 minimizes outward or "hoop"
stresses on the surrounding box during non bending, concentric operation. The thread has a relativel~ low taper angle, and it has a relatively low "break out", ~ or uncoupling force to "make up" or coupling torque ratio.
Analysis of failures of box threads for eight and a quarter inch diameter connections employing the thread of the type illustrated in Fig. 5 indicates that, in raised drilling Dperations as shown in Fig. 1, approxima~ely 90 percent of the failures caused by fatigue of the box of the member 18 where connected to the stem 14 occur in the area indicated b~ the numeral 30 in Fig. 2. The metal fatigue failure is thought to occur for a variety of reasons. The threads are under large tensile forces. The last thread on the end 1131~49~
of the pin produces a "no-tch" e~ect in the surrounding box strucLure, when a tensile load is applied to the joint. By way of illustration in Fig. 5, this would be in the area 30 adjacent the pin thread 20b. Bending ^ loads applied to the connection, force the axis 52 ' (Fig. 2) of the pin out of alignment with the a-~is of the box, (not separately shown) which increases tensile loads on the thread on the side of the thread remote from the center of bending curvature. Assume for analysis purposes, that the center of bending is to the left of the paper in Fig. 5, such as it would be for the connection 23 when illustrated as in Fig. la.
Such loads are especially detrimental at the area 30 due to the notch effect mentioned above. Such loads move the small end of the pin slightly off center with respect to the axis of the bore imparting a severe side load to the thread which causes the thread flank ¦~ 54 to tend to act like a wedge producing local stresses in the surrounding box thread which are in the same direction as the additional stress aue to the tensile loads. This wedging effect is particularl~ severe ` with the shallow l5 degree pressure flan~ thread illustrated in Fig. 5.
The sleeve design of Fig. 2 effectively prevents the small end of the pin from moving off center with -respect to the box and eliminates the wedging efect on the threads which are not centralized. Further, the sleeve design is intended to enable the threaded - 30 section to provide a better resistance to tensile loads, free of any requirements to provide centralizing of the connection. The sleeve provides a direct path for the transmission of loads perpendicular to the axis of the connection from the pin to the box and vice versa. Thus, the sleeve provides a simple but effective solution to a troublesome and costly problem.
Fig. 6 is a somewhat schematic view of an : . - - , ... .
alterna-tive form of the invention wherein a pin 60 and a box 62 are provided with cylindrical portions 64 and 66 on opposite ends of a threaded portion 68.
The cylindrical portions may mate directly with each o-ther as shown or may be formed to receive sleeves along the lines shown in Fig. 2. In either case, lateral.forces are accommodated by the cylindrical portions and thus minimize such forces on the thread area to reduce failures in pin and box connections, .
.
,
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In an earth boring drill string, rotary, shouldered connection comprising a first member called a box having internal threads and an annular end face, and a second member called a pin having external threads which mate with the box threads when the pin is inserted into the box, said pin having an axially facing annular shoulder adjacent to and extending outwardly from the last thread, the threads on said pin and box being formed such that the pin can be threaded into the box.
to the point wherein the shoulder on said pin engages the end face of said box, the outer side surface of said pin adjacent the end of the pin being substantially unthreaded, and the side surface of the inner end of said box being substantially unthreaded so that the unthreaded portion of said pin fits within said box unthreaded portion, and a sleeve positioned within the inner end of said box with the-outer surface of said sleeve snugly engaging the surrounding walls of said box unthreaded portion, and with the unthreaded surface on said pin end extending into and snugly engaging the inner wall of said sleeve, said sleeve being dimensioned and made of material which results in the sleeve providing the primary means for centering said pin end in said box and means for transmitting lateral loads between said pin end and box rather than the adjacent mating threads of the pin and box.
to the point wherein the shoulder on said pin engages the end face of said box, the outer side surface of said pin adjacent the end of the pin being substantially unthreaded, and the side surface of the inner end of said box being substantially unthreaded so that the unthreaded portion of said pin fits within said box unthreaded portion, and a sleeve positioned within the inner end of said box with the-outer surface of said sleeve snugly engaging the surrounding walls of said box unthreaded portion, and with the unthreaded surface on said pin end extending into and snugly engaging the inner wall of said sleeve, said sleeve being dimensioned and made of material which results in the sleeve providing the primary means for centering said pin end in said box and means for transmitting lateral loads between said pin end and box rather than the adjacent mating threads of the pin and box.
2. The improvement of Claim l wherein the threads of said pin and box are axially tapered to that the pin extends into said box a considerable distance before the pin is threadably engaged with the threads of the box and wherein the mating threads on the pin and the box are threadably engaged with a minimum of relative rotation between the pin and the box before said pin shoulder engages the end face of said box.
3. In an earth boring drill string connection wherein a first tubular member is formed with internal threads on one end which decrease in cross-sectional diameter from the axially outer end of the threaded portion towards the axially inner end of the threaded portion, and a second tubular member having external threads on one end which increase in cross-sectional diameter from the axially outer end of the threaded portion to the axially inner end of the threaded portion and which mate with the threads on the first member when the second member is inserted into the first member, said second member having an axially facing annular shoulder adjacent to and extending outwardly from the last thread on the axially inner end of its threaded portion, the threads on said members being formed such that the second member can be threaded into the first member to the point wherein said shoulder engages the axial end face of said first member to form a seal between the interior and exterior of said members, the modification wherein the threads on the inner end of the first member having been removed to form a cylindrical surface and wherein the threads on the outer end of the second member have been removed to form a cylindrical surface, and including a sleeve positioned between said cylindrical surfaces with the outer surface of the sleeve snugly engaging the surrounding cylindrical surface of said first member and with the cylindrical surface of said second member snugly engaging the surrounding inner wall of said sleeve, said sleeve being sufficiently incompressible.
so that lateral forces on said connection are primarily transmitted through said sleeve and said cylindrical surfaces rather than through the mating threads of said members.
so that lateral forces on said connection are primarily transmitted through said sleeve and said cylindrical surfaces rather than through the mating threads of said members.
4. The connection of Claim 3 wherein the threads on said members have a thread form with a crest and two flanks adjacent the crest with one flank having approximately a 45° angle and the other approximately a 15° angle with respect to a radial plane through said members.
5. A drill string joint connection comprising:
a first member having an internally threaded portion on one end with an internal unthreaded portion on each end of the threaded portion; and a second member having an external threaded portion on one end threaded into said threaded portion on said first member, and having unthreaded exterior portions on each end of said second member threaded portion to fit snugly within the unthreaded portions on said first member so that lateral forces applied to said connections are primarily transmitted through said unthreaded portions.
a first member having an internally threaded portion on one end with an internal unthreaded portion on each end of the threaded portion; and a second member having an external threaded portion on one end threaded into said threaded portion on said first member, and having unthreaded exterior portions on each end of said second member threaded portion to fit snugly within the unthreaded portions on said first member so that lateral forces applied to said connections are primarily transmitted through said unthreaded portions.
6. The connection of Claim 1 wherein said sleeve extends axially beyond the end of said pin to bridge the area of said box surrounding the end of said pin.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US7102079A | 1979-08-30 | 1979-08-30 | |
| US71,020 | 1979-08-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1138490A true CA1138490A (en) | 1982-12-28 |
Family
ID=22098789
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000359338A Expired CA1138490A (en) | 1979-08-30 | 1980-08-29 | Rotary shouldered connection modification |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1138490A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5188402A (en) * | 1989-01-31 | 1993-02-23 | University Of Florida | Gasket apparatus and hermetically sealed joints employing said gasket apparatus |
-
1980
- 1980-08-29 CA CA000359338A patent/CA1138490A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5188402A (en) * | 1989-01-31 | 1993-02-23 | University Of Florida | Gasket apparatus and hermetically sealed joints employing said gasket apparatus |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| EP1015802B1 (en) | Ultra high torque double shoulder tool joint | |
| US4549754A (en) | Tool joint | |
| US6120067A (en) | Threaded tool joint for connecting large tubes | |
| EP0241521B1 (en) | Seal for threaded pipe connection | |
| US6478344B2 (en) | Threaded connector | |
| EP1101056B1 (en) | Threaded and coupled connection for improved fatigue resistance | |
| US4384737A (en) | Threaded joint for well casing and tubing | |
| CA1316964C (en) | Tubular coupling with improved metal to metal seal | |
| US6511102B2 (en) | Pipe connector | |
| US4099745A (en) | Drill pipe joint | |
| US6767156B1 (en) | Thread joint and threaded components for percussive drilling components | |
| US4040756A (en) | Drill rod thread form | |
| US7513534B2 (en) | Fatigue-resistant threaded component for a tubular threaded joint | |
| US11795981B2 (en) | Threaded and coupled tubular goods connection | |
| US6041487A (en) | Method for producing sealing surfaces on a tubular member | |
| CA1138490A (en) | Rotary shouldered connection modification | |
| GB2127463A (en) | Two-piece drill bit | |
| US3447340A (en) | Resilient unit for drill strings | |
| GB2161563A (en) | Pin and box couplings | |
| RU200381U1 (en) | THREADED DRILL PIPE CONNECTION | |
| CN102425381B (en) | Drill stem connection | |
| RU202611U1 (en) | THREADED DRILL PIPE CONNECTION | |
| CA1234255A (en) | Tool joint | |
| SU1550078A1 (en) | Threaded joint of pipes | |
| CN217151858U (en) | Novel double-wall guide drill rod |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |