US3080179A

US3080179A - Slip engaging portion of drill string formed of increased wall thickness and reduced hardness

Info

Publication number: US3080179A
Application number: US845057A
Authority: US
Inventors: Carl F Huntsinger
Original assignee: HUNTSINGER ASSOCIATES
Current assignee: HUNTSINGER ASSOCIATES
Priority date: 1959-10-06
Filing date: 1959-10-06
Publication date: 1963-03-05
Anticipated expiration: 1980-03-05

Description

March 5, 1963 c. F. HUNTSINGER 3,080,179

SLIP ENGAGING PORTION OF DRILL STRING FORMED I OF INCREASED VWALL THICKNESS -AND REDUCED HARDNESS Fjiled Oct. 6, 195g: 5 Sheets-Shag: 1

li a 6?:

. IN VEN TOR. L192; II .H/A/TS/NGEE March 5, 1963 c. F. HUNTSINGER 3,080,179

SLIP ENGAGING PORTION OF DRILL STRING FORMED OF INCREASED WALL THICKNESS AND REDUCED HARDNESS Filed Oct. 6, 1959 INVENTOR.

(be; EHU/VT-S/NGEE 14 77-0 A/EY.

March 5, 1963 v c. F. HUNTSINGER 3,080,172

' sup ENGAGING PORTION OF DRILL STRING FORMED v OF INCREASED WALL THICKNESS AND REDUCED HARDNESS Filed Oct. 6, 1959 a Sheets-Sheet s 2! 5 5i 4 p40! a0 INVENTOR.

, I CARL E Hwvrswaee BY The present invention relates to rotary well drilling equipment and more particularly to tubular drill string members to be disposed in the well bore for rotating a drill bit, or the like, connected to its lower end. The tubular drill string may consist of drill pipe, light weight drill pipe, drill tubing, or drill casing. For convenience of reference, such tubular members may be classified as drill pipe. This application is a continuation-in-part of my application for Tubular Drill String Member for Drilling Well, Serial No. 810,035, filed April 30, 1959 and now abandoned.

The tubular drill string disposed in the well bore, to

the lower end of which the drill bit is attached, consists of a plurality of drill pipe members threadedly attached to one another. The threaded connections between the drill pipe sections are referred to as tool joints, a male tool joint on one section being threadedly attached to the female tool joint of an adjoining section.

During the operation of drilling the oil well, the drill bit eventually becomes dull or is to be changed for some other reason. Accordingly, the entire string of drill pipe is elevated in the well bore and the joints of drill pipe disconnected from one another by unthreading the sections removed from the hole from the sections that remain in the well bore. After the drill bit has been withdrawn from the Well bore, a new bit is attached to the lower end of the drilling string and the bit is inserted in the well bore, the tool joints being successively threadedly attached to one another and the entire assembled drill string lowered in the well bore until the new bit reaches the bottom of the hole, whereupon drilling is resumed. 'Normally, in drilling an oil well, a plurality of drill bits are used, requiring lowering and elevation of the entire drill string in the well bore for a plurality of round trips.

During the making of a round trip, drill pipe sections above the-rotary table at the top of the well bore are threaded or unthreaded from the drill string disposed therebelow. The lower portion of the string of drill pipe is suspended or hung in the hole by a slip assembly that usually consists of a plurality of segmentel slips having inner teeth adapted to engage and grip the exterior of a pipe section and outer downwardly tapering surfaces adapted to fit in a companion tapered surface of a slip bowl. The weight of the string of drill pipe hanging in v the well bore tends to move the slips downwardly, wedging them in the bowl and producing an inward force that causes the slip teeth'to tend to penetrate into the drill pipe section that they engage. With relatively long strings of drill pipe in the well bore, the downward force is correspondingly greater, causing the radial pressure of the slips upon the pipe'section to be increased, and tending to elongate the pipe section where it is gripped by the slips, or collapse the section inwardly. The force imposed by the string of drill pipe itself is oftentimes greatly increased by the fact that it is very often caught by the slip assembly during its lowering in the well bore, instead of being brought to a full rest prior to application of the slips thereby introducing an impact load upon the slip assembly, caused by the jamming of the slips in the bowl and their inward pressure upon the pipe area which they grip.

During the unthreading and threading operations, in disice connecting or reconnecting each tool joint, tongs are used, which are placed upon the adjacent tool joints of the upper and lower sections. At times, the tongs gripping the lower section will slip or turn during the time that the upper tong is being used to either make or break the threaded connection, eifecting a rotation of the lower string of drill pipe in the slip assembly, causing the hard slip members to tend to mar or tear the surface of the drill pipe that they engage. Such action can effect a cutting and tearing of the pipe in the slip affected area.

During certain special threading or unthreading operation in disconnecting or reconnecting each tool joint, it is not practical to place the tongs on the tool joints, but rather to place the tongs directly on the drill pipe. Also, certain types of drill pipe have no tool joint connections but, rather, have the threaded connections directly on the drill pipe. Tongs also have sharp and hardened inserts to better grip the tool joints or drill pipe. The results of placing the tongs directly on the drill pipe will often effect a cutting, tearing or notching action similar to that produced by the slip segment teeth when applied to the drill pipe. The gripping action applied by the tongs to the drill pipe will often produce a localized crushing action. The above tendency for the pipe section subjected to the gripping forces of the slips or tongs at the top of the well bore to be elongated or collapsed inwardly is more pronounced when lighter weight and higher strength drill pipe is used. Such use is dictated by increased hole depth, and also by the desire to have a larger inside diameter through the string of drill pipe to permit the pumping of greater volumes of drilling fiuid through the drill pipe to remove the cuttings at an increased rate and enhance penetration of the drill bit in the bottom of the well bore.

Lighter drill pipe weights enable less expensive surface equipment to be used inasmuch as such equipment does not have to support comparatively heavy loads.

When comparatively light weight drill pipe is used, it is of a type that had to be heat treated in order to increase its physical properties. The particular heat treatment employed results in a hardening of the steel of which the drill pipe is made, an increase inits strength, and a decrease in its ductility. The heat treatment also results in the steel becoming more notch sensitive to cuts, tears or notches caused by slip or tong teeth than softer or lower strength steels. The notching of the exterior of a drill pipe section by the slips may be a source of fatigue failure, and may ultimately result in. a twistoif or other disruption of the drill pipe at the location of the notch. The notching of a comparatively hard steel is potentially much more hazardous than that of a soft steel since the notch or crack produced thereby advances much more rapidly, probably due to the fact that the metal does not yield to any appreciable extent to distribute the stress to which the pipe is subjected in the region of the notch.

It is evident that the relatively thin wall drill pipe is more susceptible to inward crushing by the slips or tongs and to the provision of cracks resulting from the notching of the outer portions of the drill pipe section subjected to the slip segment teeth, or to the tong segment teeth.

Accordingly, it is an object of the present invention to provide a tubular drill pipe section of relatively light weight and thin wall thickness that is capable of better withstanding the inward crushing force of the slips and tongs at the top of the well bore and which has less notch sensitivity so as to be less conducive to fatigue failure.

Another object of the invention is to provide a drill pipe section of a composite character and in which the main portion of the pipe section is made of a material having-a relatively high unit strength, such main portion having a 3. relatively thin wall thickness in comparison to its outside diameter. The drill pipe section at the area that will be engaged by the slips or tongs at the top of the well bore: is made of a metal that has a greater wall thickness in comparison to. itsdiameter so as to resist inward crushing by the slips or tongs, such metal also having less notch sensitivity, so as to be less susceptible to fatigue failure resulting from notches produced by the slips or tongs at the top of the well bore. A drill pipe section is thus producedv of comparatively light weight throughout its'over-all length, because of its comparatively thin wall thickness, and which resists inward crushing of the slips or tongs and has less notch sensitivity. The metal having the greater wall. thickness and which is gripped by the slips or tongs can be of a lower grade than the main portion of the drill pipe section, but in view of its greater wall. thickness, it will be capable of withstanding the same loads as the main drill pipe section in tension, torsion, bending, and compression. This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of general forms in which it maybe embodied. These forms are shown in the drawings accompanying and forming part of the present specification. They will now be described in detail, for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since thescopeofthe inventionis best defined by the appended claims.

Referring to the drawings:

FIGURE 1 is a side elevational view of a string of drillipipe embodying the invention;

FIG. 2 is alongitudinal'section through the upper portionof. a drill. pipe section, the lower portion beingshown in side elevation;

FIG. 3 is alongitudinal section through the lower portion ofadrill. pipe section, the upper portion thereof being shown in side elevation;

FIG. 4 isa side elevational viewv of a modification of the drilllpipeshown in FIG. 1;

FIG; 5 is alongitudinal section, partly shown in side elevational, through the drill pipe section illustrated in FIG. 4;

FIG. 6. is. a longitudinal section, partly shown in side elevation, through another embodiment of a drill pipe section;

FIG.v 7 is a longitudinal section,. Partly shown in side l'evatiori, .of, a portion of still another drill pipe section;

FIG. 8 is a longitudinal section, partly in side elevation, of a portion of yet a further form of drill pipe section;

FIG. 9 is allongitudinal' section, with a portion illustr'atedv in side elevation, of yet another embodiment of drill pipe section.

, As disclosed in FIGS. 1 to 3' of the drawings, a drillings'tringlO includes a plurality of drill pipe sections 11, 12, 13 th'r'ad'edly attached to one another. The upper end of each section may be constituted asv a tool joint 14 having a threaded box 15 adapted to be threadedly connected to the lower threaded pin 16 of a tool joint 17 at an adjacent upper drill pipesection. The. tool joints are suitably secured to the intervening pipe 18 of each section in any'suitable manner. As specifically. disclosed, the lower tool joint 17 is connected to the adjacent portion. 18 of the pipe by a flash or pressure weld 19. The upper main portion of the drill pipe 18 is connected to a length. of protector tube 20, as by means of a flash or pressure weld 21, and the upper end of such protector tube section is, in turn, connected to the upper tool joint 14 by means of a flash or pressureweld 22. Although the drawings specifically disclose the flash or pressure welds for securing the several parts to one another, it is to 4 tool joint 17 may be made integral with the main length of drill pipe 18.

The main length of drill pipe 18 has a comparatively thin wall thickness T in relation to its external diameter D for the purpose of providing a lightweight pipe section 18 and to furnish an increased cross-sectional passage area P through which the drilling mud pumped down the drilling string can flow, so as to minimize the frictional resistance to flow of the drilling mud through the string of drill pipe and insure its delivery at a greater volumetric rate through the drill bit (not shown). At the lower tool joint 17, the main section of drill pipe 18 has its wall thickness H increased by decreasing its internal diameter to conform to the internal diameter of the lower tool joint section 17. Similarly, the upper portion of the main drill pipe section has its wall thickness M increased by decreasing its internal diameter, such internal diameter being essentially the same as the internal diameter through the lower tool joint 17. The upper tool joint 14 also has an internal diameter substantially conforming to the internal diameter through the lower tool joint 17, and the intermediate section of protector tubing 20 also preferably has an internal diameter substantially the same as the internal diameter of the tool joints 14, 17 and an external diameter substantially the same as the outside diameter of the main drill pipe section 18. The protector tube 20 is placed adjacent to the upper tool joint 14, which is the region-of the drill pipe section normally engaged by the toothed slips 50 at the top of the well bore when disposed in a slip bowl 51 mounted in the usual rotary table 52. Such protector tube is of such a length as to insure that the entire length of the slip teeth will engage such section, and not the main drill pipe section 18 therebelow. For example, the protector tube portion 20 of the drill pipe member may be about fortytwo inches in length; whereas the entire

drill pipe section

14, 20, 18, 17 may be about thirty feet in length.

The main portion 18 of the drill pipe section is made of a relatively high strength steel that has been heat treated. Such steel has a comparatively high ultimate tensile strength, a comparatively high yield strength, and a relatively low elongation; Its hardness is also relatively high- As an example, the portions of the drill pipe. section. just referred to may be grade P- drill tubing. having the following physical characteristics:

Despite its highv strength, such steels, or steels similar toit, have high notch sensitivity, and in view of the fact that the wall thickness T of the pipe section. is comparatively small, such steels are susceptible to inward crushing by the slipsat the top. of the Well home. However, the protector tube section 20 has an ultimate tensile strength and yield strength that is substantially lower than that of the main portion .18 of the drill pipe section, while its elongation is substantially higher. I-ts hardness is also substantially lower. By way of example, the protector tubular section 2-0 that is to be engaged by the slips at the top of the well bore may be made from grade B tubing, which has the following physical characteristics:

Ultimate tensile strength .p.s.i 118,800 Yield' strength p.s.i 84,400

.material between the upper tool joint 14 the weight per foot over only a Elongation percent 23.0 Rockwell hardness No. (1-22-25.

and the following chemical analysis:

Percent Carbon 0.37 Manganese 0.93 Silicon 0.16 Molybdenum 0.03

The grade B drill pipe 20 has a much greater wall thickness than the underlying portion of the tubular member, and since its outside diameter D to Wall thickness M is much less than the corresponding outside diameter D to wall thickness T of the main section of the tubular member, it is capable of withstanding inward crushing to a much greater extent than the main portion 13 of the tubular member. Since it is also not as hard as the main portion of the tubing section, it has lesser notch sensitivity, and despite the penetration of the slips, or other toothed members, such as tong segments, into its surface, fatigue failures do not result.

Despite the fact that the unit strength of the protector tube 20 is somewhat less than that of the main portion 18 of the drill pipe section, it is capable of withstanding at least the same tensile loads, compressive loads, bending loads and torques. This is due to the fiact that its crossssectional area is greater than the cross-sectional area of the main portion 18 of the drill pipe section. Its greater wall thickness, which is provided by having substantially the same outside diameter as the main portion 18 of the drill pipe section, and an inside diameter that is no less than the inside diameter through the adjacent tool joint 14, results in a considerable increase in its resistance to inward crushing by the slips.

By way of example, the drill pipe, with the exception of the protector tube portion 20, may be made of grade P-l05 steel. The main portion 18 of the drill pipe section may be of 3 /2 inches 0.1)., and have a Weight of 9.2 lbs. per foot. Assuming that the grade P-l05 pipe has a guaranteed minimum yield strength of 105,000 p.s.i., and that the protector tube portion 20 is made of grade E pipe having a guaranteed minimum yield strength of 75,- 000 p.s-.i., the protector tube portion will have the same tensible strength as the main portion of the drill pipe-if the weight per foot of the protector tube is 9.2 105,000+7s,e00=12.9 lbs. per foot Typically, the protector tube 20 with the grade E material that is used can have a weight of 13.3 lbs. per foot. By inserting such a Weight of grade B and the main portion 18 of the drill pipe section, the protector tube 20 will have a tensile strength at least equal to that of the main portion of the drill pipe section. In the examples given, a grade P-105 pipe section has a yield strength in crushing of approximately 7,000 lbs., while the protector tube has a yield strength in crushing of approximately 26,000 lbs. Accordingly, the crushing yield 1 strength of the protector tube 20 is almost four times that the drill pipe string, while short length of about three to four feet has been increased by less than fifty percent. This has been done without restricting the passage through the section 241 of drill pipe below that of the inside diameter through the usual tool joints 14, 17.

It is, accordingly, apparent that :a drill pipe section has been provided in which a heavier cross-sectional area of pipe 2%) is present at the region of engagement with the slips at the top of the well bore, which will better resist of the main portion 18 of localized crushing under the action of the slip segments.

Despite the fact that the protector tube section has a lesser unit tensile strength than the main portion 18 of the drill pipe section, the elongation due to excessive tensile loads will be no greater because of the much heavier cross-sectional area of the protector tube. The

material of which the protector tube is made has a much lower notch sensitivity than the main portion 18 of the drill pipe section, and, therefore, offers less opportunity for fatigue cracks to develop, with potential resultant fatigue failure at the region of engagement of the pipe by the slips. If the protector tube 20 becomes excessively marred by the slip teeth, it can easily be cut out and a new section inserted in its place, thereby avoiding the necessity for scrapping the entire length of drill pipe.

Although the protector tube disclosed in FIGS. 1, 2 and 3 has been described in connection with the application of slips to the protector tube section 20, it is also applicable to the engagement of such protector tube portion by tongs having sharp and hardened inserts. The teeth of such tongs can have the same harmful effect-on the .drill pipe section as described above specifically in connection with engagement of slips with a drill pipe section. Moreover, the protector tube portion 24 can be applied between the lower tool joint 17 and the main portion 18 of the drill pipe section as well as between the upper tool joint 14 and the drill pipe section 18 as shown in FIGS. 4 and 5. When located between the lower tool joint 17 and the main drill pipe section 18, the protector tube section 2.0 will ordinarily be engaged by tongs having the sharp and hardened inserts. Such lower protector tube portion will better Withstand the cutting, tearing, not-ching and localized crushing action of the tong segments than the main portion 18 of the drill pipe section, which is of high strength and has greater susceptibility to notching andlocalized crushing.

In the form of invention disclosed in FIG. 6, a drill pipe section 12 has a flush internal diameter throughout its length, that is to say, the internal diameter through the tool joints 14, 17 and protector tubes 213a the same as the internal diameter through the main portion 18a of the pipe section. The main portion or length 18a of the pipe section has its wall thickness M increased at each of its upper and lower parts by increasing its external diameter, and this external diameter will conform to the external diameter of each protector tube 211a, which has the greater Wall thickness M than the lesser Wall thickness T of the main section 1&1 of the drill pipe. As in the forms of invention previously described, the main portion 18a is connected to each protector tube 20a, as by means of a flash or pressure weld 21. The end of each protector tube remote from the main portion 18a can also be connected to its adjacent tool joint 14, 17 in any suitable manner, as by means of a flash or pressure weld 22.

Again, in lieu of the flash or pressure weld, the several parts can be threadedly attached to one another.

In all respects, the drill pipe section disclosed in'FIG. 6 is the same as that illustrated in FIGS. 2 and 5, in that each protector tube Zi a is made of a material having a lesser unit strength than the main portion 18a of the drill pipe section, which is compensated for by the fact that its wall thickness is much greater. In this instance, the greater wall thickness is secured by increasing the outside diameter of the protector tube 212a rather than decreasing the inside diameter, as illustrated in FIGS. 2 and 5. Thus, inward crushing action of slips or tong segments is resisted. The fact that the protector tube portion 20:: is not as hard as the main portion 18a of the V for attachment to the adjacent tool joint.

drill pipe section renders it less susceptible to notching, minimizing, if not fully eliminating, fatigue failures.

In the form of invention disclosed in FIG. 7, the main portion 18b of the drill pipe section 12 may be Welded or otherwise secured to an upper tool joint 14 or a lower tool joint 17, or to both upper and lower tool joints 14, 17, the ends of the main portion being thickened to provide a larger wall thickness M and cross-sectional area Each thickened area, in efiect, provides a shoulder 36 against which a tube 2% abuts that is placed over the main portion 15b of the drill pipe section and along a particular length of such section, which may be three to four feet, for example. A tube 2% can be first heated and then slipped over the main portion of the drill pipe section until it engages the shoulder 30. Upon cooling, the tube 20b shrinks upon the pipe section and is thus firmly secured thereto. If desired, the tube 20b can be slipped over the drill pipe section 18b and then welded thereto at its upper and lower ends, as indicated at 21, 22.

The tube 2012 adds to the thickness of the drill pipe at the region of engagement by the slips of the rotary table or by the toothed tong segments, and thereby provides a composite drill pipe section which is better able to withstand the inward crushing action of the slips or tongs. Moreover, the tube 2% may be made of a steel having essentially the same physical characteristics as the steel described above from which the

protector tube sections

20 and 20a are made, which steel is not as hard as the steel of which the main tubing section 18b is made, and which will, therefore, have a lesser notch sensitivity so that fatigue failures do not result, regardless of the penetration of the slip or tong segment teeth thereinto.

In the form of invention disclosed in FIG. 8, the protector tube 20c is disclosed as being integral with the adjacent tool joint 14, 17, and is attached to the main portion or length 18a of the drill pipe section 12 With an internal flush fluid passage through the tool joint, protector tubes and main tubing section. The drill pipe section is essentially the same as disclosed in FIG. 6, with the exception that each tool joint is integral with the adjacent protector tube portion 20c. In other words, each tool joint and adjacent protector tube portion 200 are made from the same steel, have much lesser notch sensitivity than the steel of the main section 18a and are better capable of withstanding inward crushing. Accordingly, it is only necessary to provide a separate welded or threaded connection 21 between the end of the protector tube portion remote from the tool joint and the adjacent end of the main portion 18a of the drill pipe section.

In the form of invention disclosed in FIG. 9, the protector tube portion 20d having the greater wall thickness is integral with the main portion or length 180 of the drill pipe section and is made from a steel having the same chemical analysis. Each protector tube portion 20d is made of a suitable length, such as three to four feet, and has a greater wall thickness M than the thickness T of the main portion of the section. It is welded, or otherwise secured, to the adjacent tool joint 14, 17. However, the heat treatment of the main portion 180 of the tubular member or drill pipe section is diiferent from the heatv treatment of the protector portion 20d in order to provide the proper characteristics to these different portions. As an example, the entire drill pipe section 12 can be heat treated to provide the appropriate physical characteristics desired in the thin wall portion T of the section, including high ultimate tensile strength, high yield strength, relatively low elongation and relatively high hardness. Each protector tube portion 20d is then made softer so that it is less notch sensitive by simply tempering the length of the protector tube 20d in a subsequent tempering operation without reheating the main thin wall portion 18c of the pipe section.

Another manner of securing the desired physical characteristics in themain portion 180 of the drill pipe section 12 and in the protector tube portion 20d is to normalize the full length of the drill pipe 12 and then air quench the entire pipe section 12. Since each protector tube portion 20d is heavier than the thin wall main portion 180 of the pipe section, the cooling rate of each protector tube portion is appreciably'slower than the main portion, with a resultant lower unit strength and hardness in the thicker wall protector tube portions 20d.

The device illustrated in FIG. 9 can be made in several manners prior to its heat treatment. It can be hot rolled to the desired outside diameter of the protector tube portions 20d and the desired wall thickness. It

can then be cold drawn through a split die on a draw bench to achieve the reduced wall thickness T of the main portion of the pipe. The constant internal diameter through the main portion 1-8c and each protec tor tube portion 20d can be maintained with a punch; whereas the split die accomplishes the change in outside diameter from the lesser diameter of the main length 180 of the drill pipe section to the greater diameter of the protector tube portions 20d.

The inventor claims:

1. A tubular drill pipe section to be used in a well bore comprising upper and lower tool joints, a main steel tubular portion extending upwardly from said lower joint and terminating near said upper tool joint, and an elongate steel protector tube extending downwardly from said upper tool joint and secured to the upper end of said main portion, said main portion having a much lesser wall thickness throughout substantially its entire length than said protector tube and being made of a steel having substantially greater hardness and unit tensile and torsional strength than the steel of said protector tube, the length of said protector tube being about at least four times the outside diameter of said main portion and said protector tube being disposed in said drill pipe section at a location for engagement by supporting slips at the top of the well bore, the cross-sectional area of said protector tube being such that the total tensile and torsional strength of said protector tube is no less than the total tensile and torsion-a1 strength of said main portion, whereby said protector tube has less notch sensitivity and greater resistance to inward crushing than said main portion to the action of the slips.

2. A tubular drill pipe section to be used in a well bore comprising upper and lower tool joints, a main steel tubular portion extending upwardly from said lower joint and terminating near said upper tool joint, and an elongate steel protector tube extending downwardly from said upper tool joint and secured to the upper end or said main portion, said main portion having a much lesser wall thickness throughout substantially its entire length than said protector tube, the wall thickness of said main portion adjacent said protector tube being substantially the sameas the wall thickness of said protector tube, said main portion being made of a steel having substantially greater hardness and unit tensile and torsional strength than the steel of said protector tube, the length of said protector tube being about at least four times the outside diameter of said main portion and said protector tube being disposed in said drill pipe section at a location =for engagement by supporting slips at the top of the well bore, the cross sectional area of said protector tube being such that the total tensile and torsional strength of said protector tube is no less than the total tensile and torsional strength of said main portion where it has the aforesaid lesser wall thickness, whereby said protector tube has less notch sensitivity and greater resistance to inward crushing than said main portion to the action of the slips.

3. A tubular drill pipe section to be used in a well bore comprising upper and lower tool joints, a main steel tubular portion extending upwardly from said lower joint and terminating near said upper tool joint, and an elongate steel protector tube extending downwardly from said upper tool joint and secured to the upper end of said main portion, said main portion having a much lesser wall thickness throughout substantially its entire length than said protector tube and being made of a steel having substantially greater hardness and unit tensile and torsional strength than the steel of said protector tube, the length of said protector tube being about at least four times the outside diameter of said main portion and said protector tube being disposed in said drill pipe section at a location for engagement by supporting slips at the top of the well bore, the cross-sectional area of said protector tube being such that the total tensile and torsional strength of said protector tube is no less than the total tensile and torsional strength of said main portion, the inside'diameter of said protector tube being no less than the inside diameter of said upper tool joint, where by said protector tube has less notch sensitivity and greater resistance to inward crushing than said main portion to the action of the slips.

4. A tubular drill pipe section to be used in a well bore comprising upper and lower tool joints, 2. main steel tubular portion extending upwardly from said lower joint and terminating near said upper tool joint, and an elongate steel protector tube extending downwardly from said upper tool joint and secured to the upper end of said main portion, said main portion having a much lesser wall thickness throughout substantially its entire length than said protector tube, the wall thickness of said main portion adjacent said protector tube being substantially the same as the wall thickness of said protector tube, said main portion being made of a steel having substantially greater hardness and unit tensile and torsional streng-th than the steel of said protector tube, the length of said protector tube being about at least four times the outside diameter of said main portion and said protector tube being disposed in said drill pipe section at a location for engagement by supporting slips at the top of the well bore the cross-sectional area of said protector tube being such that the total tensile and torsional strength of said protector tube is no less than the total tensile and torsional strength of said main portion where it has the aforesaid lesser wall thickness, the inside diameter of said protector tube being no less than the inside diameter of said upper tool joint and the inside diameter of said main portion adjacent said protector tube, whereby said protector tube has less notch sensitivity and greater resistance to inward crushing than said main portion to the action of the slips.

5. A tubular drill pipe section to be used in a well bore and adapted to be engaged by gripping slip segments or tong segments used in supporting and threadedly attaching or unthreading drill pipe sections to or from one another, comprising upper and lower tool joints, a main steel tubular portion between said joints, and an elongate steel tubular protector portion between and secured to said main portion and one of said joints and adapted to be engaged by gripping segments, said main portion having a much lesser wall thickness throughout substantially its entire length than said protector portion, the steel of said main portion having different physical characteristics than the steel of at least the outer portion of said protector portion, such that said main portion has substantially greater hardness and unit tensile and torsional strength than the steel of said outer portion, the length or" said protector portion being about at least four times the outside diameter of said main portion, the cross-sectional area of said protector portion being such that the total tensile and torsional strength of said protector portion is no less than the total tensile strength of said main portion, whereby the outer portion of said tubular protector portion has less notch sensitivity than said main portion to the action of the gripping segments and said tubular protector portion has greater resistance to inward crushing than said main portion to the action of the gripping segments.

6. A tubular drill pipe section to be used in a well bore and adapted to be engaged by gripping slip segments or tong segments used in supporting and threadedly attaching or unthreading drill pipe sections to or from one another, comprising upper and lower tool joints, a main steel tubular portion between said joints, and an elongate steel tubular protector portion between and secured to said main portion and one of said joints and adapted to be engaged by the gripping segment, said main portion having a much lesser wall thickness throughout substantially its entire length than said protector portion, the steel of said main portion having different physical characteristics than the steel of said protector portion, such that said main portion has substantially greater hardness and unit tensile and torsional strength than the steel of said rotector portion, the length of said protector portion being about at least four times the outside diameter of said main portion, the cross-sectional area of said protector portion being such that the total tensile and torsional strength of said protector portion is no less than the total tensile and torsional strength of said main portion, whereby said tubular protector portion has less notch sensitivity and greater resistance to inward crushing than said main portion to the action of the gripping segments.

7. A tubular drill pipe section to be used in a well bore and adapted to be engaged by gripping slip segments or tong segments used in supporting and threadedly attaching or unthreading drill pipe sections to or from one another, comprising upper and lower tool joints, a main steel tubular portion between said joints, and an elongate steel tubular protector portion integral with said main portion and secured to one of said joints and adapted to be engaged by the gripping segments, said main portion having a much lesser wall thickness throughout substantially its entire length than said protector portion, said main portion and protector portion being composed of steel having the same chemical analysis, but having different physical characteristics, such that said main portion has substantially greater hardness and unit tensile and torsional strength than the steel of said protector portion, the length of said protector portion being about at least four times the outside diameter of said main portion, the cross-sectional area of said protector portion being such that the total tensile and torsional strength of said protector portion is no less than the total tensile and torsional strength of said main portion, whereby said tubular protector portion has less notch sensitivity and greater resistance to inward crushing than said main portion to the action of the gripping segments.

8. A tubular drill pipe section to be used in a well bore and adapted to be engaged by gripping slip segments or tong segments used in supporting and threadedly attaching or unt-hreading drill pipe sections to or from one another, comprising upper and lower tool joints, a main steel tubular portion between said joints, and an elongate steel tubular protector portion between said main portion and one of said joints and adapted to be engaged by the gripping segments, said protector portion having an inner portion integral with said main portion and secured to said one joint and also having an outer portion encompassing said inner portion, said main portion having a much lesser wall thickness throughout substantially its entire length than said protector portion, the steel of said main portion having different physical characteristics than the steel of said outer portion, such that said main portion has substantially greater hardness and unit tensile and torsional strength than the steel of said outer portion, the length of said protector portion being about at least four times the outside diameter of said main portion, the cross-sectional area of said protector portion being such that the total tensile and torsional strength of said protector portion is no less than the total tensile and torsional strength of said main portion, whereby the outer portion of said tubular protector portion has less notch sensitivity than said main portion to the action of the gripping segments and said tubular protector portion has greater resistance to inward crushing than said main portion to the action of the gripping segments.

9. A tubular drill pipe section to be used in a well bore and adapted to be engaged by gripping slip segments or tong segments used in supporting and threadedly attaching or unthreading drill pipe sections to or from one another, comprising upper and lower tool joints, a main steel tubular portion between said joints, and upper and lower elongate steel protector portions between and secured to said main portion and said joints, each of said protector portions being adapted for engagement by the gripping segments, said main portion having a much lesser wall thickness throughout substantially its entire length than each of said protector portions, the steel of said "main portion having difierent physical characteristics than the steel of at least the outer portion of each of said protector portions, such that said main portion has substantially greater hardness and unit tensile and torsional strength than the steel of the outer portion of each of said protector portions, each of said protector portions having a length about at least four times the outside diameter of said main portion, the cross-sectional area of each of said protector portions being such that the total tensile and torsional strength of each of said protector portions is no less than the total tensile and torsional strength of said main .portion, whereby the outer portion of each of said tubular protector portions has less notch sensitivity than said-main portion to the action of the gripping segments and each of said tubular protector portions has greater resistance to inward crushing than said main portion to the action of the gripping segments.

References Cited in the file of this patent UNITED STATES PATENTS 1,236,145 Burns Aug. 7, 1917 1,613,461 Johnson Jan. 4, 1927 1,714,813 Reed May 28, 1929 1,973,848 Duffy Sept. 18, 1934 1,993,269 Fletcher M31. 5, 193 5 2,257,335 Evans et a1 Sept. 30, 1941 2,340,706 SOmeS Feb. 1, 1944 FOREIGN PATENTS 129,918 Australia June 18, 1946 849,532 Ger-many Sept; 15, 1952 865,883 German F65. 5; 1953

Claims

1. A TUBULAR DRILL PIPE SECTION TO BE USED IN A WELL BORE COMPRISING UPPER AND LOWER TOOL JOINTS, A MAIN STEEL TUBULAR PORTION EXTENDING UPWARDLY FROM SAID LOWER JOINT AND TERMINATING NEAR SAID UPPER TOOL JOINT, AND AN ELONGATE STEEL PROTECTOR TUBE EXTENDING DOWNWARDLY FROM SAID UPPER TOOL JOINT AND SECURED TO THE UPPER END OF SAID MAIN PORTION, SAID MAIN PORTION HAVING A MUCH LESSER WALL THICKNESS THROUGHOUT SUBSTANTIALLY ITS ENTIRE LENGTH THAN SAID PROTECTOR TUBE AND BEING MADE OF A STEEL HAVING SUBSTANTIALLY GREATER HARDNESS AND UNIT TENSILE AND TORSIONAL STRENGTH THAN THE STEEL OF SAID PROTECTOR TUBE, THE LENGTH OF SAID PROTECTOR TUBE BEING ABOUT AT LEAST FOUR TIMES THE OUTSIDE DIAMETER OF SAID MAIN PORTION AND SAID PROTECTOR TUBE BEING DISPOSED IN SAID DRILL PIPE SECTION AT A LOCATION FOR ENGAGEMENT BY SUPPORTING SLIPS AT THE TOP OF THE WELL BORE, THE CROSS-SECTIONAL AREA OF SAID PROTECTOR TUBE BEING SUCH THAT THE TOTAL TENSILE AND TORSIONAL STRENGTH OF SAID PROTECTOR TUBE IS NO LESS THAN THE TOTAL TENSILE AND TORSIONAL STRENGTH OF SAID MAIN PORTION, WHEREBY SAID PROTECTOR TUBE HAS LESS NOTCH SENSITIVITY AND GREATER RESISTANCE TO INWARD CRUSHING THAN SAID MAIN PORTION TO THE ACTION OF THE SLIPS.