Note: Descriptions are shown in the official language in which they were submitted.
1 ~2d~!9~3
BACKGROUND O~ THE INVENTION
This in~ention relates in general to earth boring
drill pipe, and in particular to the tool joints for connecting
the sections of drill pipe together.
Deep wells such as for oil and gas are drilled with a
rotary drill bit rotated by a string of drill pipe. The drill
pipe is made-up of indi~idual members, each about 30 foot in
length. The members are secured together by a threaded
connection, called a tool joint. The tool joints must with-
stand the normal torque encounted during drilling, and also
pro~ide sealing to prevent drillin~ fluid being pumped down
the drill pipe from leaking out the joints. Leakage out the
tool joints causes wear due to the abrasiveness of the drilling
fluid, which would lead to early fallure.
The tool joint is made-up of a pin member and a box
member. The pin member has external threads and an external
annular make-up shoulder. The box member has internal threads
and a rim or face that makes up against the make-up shoulder.
In conventional drill pipe, there is no internal shoulder in
the box member for contact by the nose or face of the pin.
When the tool joint members are made-up at the surface, normally
they will be made-up to a tor~ue that exerts a pressure that is
; about one-half the yield strength between the box face and pin
~ make-up shoulder.
i ~ 4 ~ ~
Should additional torque be encountered while drilling,
such as due to the bit or pipe becoming stuck, it is possible
~or the yield strength of -the pin and box to be exceeded and to
part. Consequently, it is very important to have tool joints
with high torque withstanding abilities, preferably in excess
of the drill pipe itself.
SUMMARY OF THE INVENTION
In this invention, a tool joint is provided that has
a substantially increased yield stren~th without any additional
thickness in the pin or box, and without further hardening
of the steel. The box is provided with an internal shoulder
located below its threads. The pin has a face on the end of
its nose that mates with the internal shoulder in the box.
The dimensions of the pin and box are calculated so that when
hand tightenedl the box face will contact the external shoulder
of the pin. A clearance, however, will exist between the pin
face and the internal shoulder of the box. ~hen the tool
joint is fully made-up to its normal make-up torque, the box
face will engage the external make-up shoulder to the normal
pressure, which is about one half the yield strength of the
tool joint. The pin face will exert little or no pressure
against the internal shoulder at normal make-up torque.
During drilling operation, if additional torque is
encountered, the joint will further tighten, causing the
pin face to engage and tighten against the internal shoulder.
The counterbore of the box, and the base and nose sections
of the pin are selected so that the nose section of the pin
will reach its yield strength approximately the same and
no later than the time at which the box counterbore and
pin base reach their yield strengths. The internal make-up
shoulder increases the amount of torque required to part
the tool joint.
2 'i 9 ~
BRIEF DESCRIPTI~N OF _HE DRAWINGS
Fig. 1 is the sole figure, and it shows a cross-
sectional view of a tool joint constructed in accordance
with this invention,
DESCRIPTION OF THE PREFERRED EMBODIME~T
Fig. 1 shows an upper drill pipe member 11 secured
into a lower drill pipe member 13. The ends of the drill
pipe members 11 and 13, when connected together, are ~nown
as a tool joint. A pin 15 is formed on the lower end o~
upper drill pipe member 11, and also on the lower end (not
shown) of the lower drill pipe member 13. Pin 15 has an
external, annular make-up shoulder 17. A relief groove 19
is located at the inner diameter of external shoulder 17.
A base section 21 extends downward from external
should 17. Base section 21 is cylindrical and does not
contain any threadsO A bench mark shoulder 23 is formed a
short distance downward from make-up shoulder 17 for use
in measuring the amount of metal removed from make-up
shoulder 17 when redressed. A set oE threads 25 is formed
on pin 15 helow base section 21. Threads 25 are tapered
; and terminate in a cylindrical nose section 27. Nose section
27 terminates in a face ~9, which is a circular rim located
in a plane perpendicular to the axis of the drill pipe
member 11.
~5 The upper end of lower drill pipe member 13, as well
as the upper end (not shown) of the upper drill pipe
member 11, has a box 31 formed on it. Box 31 receives pin
15 and includes a rim or face 33 on its upper extremity.
Face 33 is a circular, flat surface located in a plane
perpendicular to the axis of lower drill pipe member 13,
Face 33 engages external shoulder 17 of pin 15. The inner
bore of box 31 includes an upwardly facin~ shoulder 35 formed
a short distance below face 33 for servin~ as a bench mark.
2~a
Bench mark 35 enables the user to determine how much metal
has been removed from face 33 during redressing operations.
~ cylindrical counterbore section 37 is located
immediately below bench mark 35. Counterbore section 37
extends about the same length as base section 21, but has an
inner diameter that is greater than the outer diameter of
base section 21. This results in an annular cavity between
the base section 21 and counterbore section 37. A set of
internal threads 39 are located below the counterbore
section 37. Threads 39 are tapered and sized to engage
threads 25.
Box 31 has a cylindrical base section 41 located
below threads 39. Base section 41 terminates in an annular
upwardly facing internal shoulder 43. Shoulder 43 is located
ir, a plane perpendicular to the axis of lower drill pipe
member 13, and is adapted to be engaged by pin face 29. A
relie~ groove 45 is formed at the intersection of internal
shoulder 43 and base section 41. An axial passage 47 of
box 31 below internal shoulder 43 is equal tc, the diameter
of an axial passage 49 of pin 15. An annular recessed area
51 is formed on the exterior sidewall of counterbore section
37, Recessed area 51 has a slightly smaller diameter than
the outer diameter of the portion con-taining threads 39.
The box 31 and pin 15 are dimensioned so that the
distance from the external shoulder 17 to pin face 29 is
slightly less than the dis-tance from the box face 33 to
internal shoulder 43. The box 31 and pin 15 are dimensioned
so that at the surface, when two members 11 and 13 are made~
up manually hand tight without the use o~ wrenches or tools,
a clearance will exist between pin face 29 and internal
shoulder 43. At hand tight, there will be no pressure between
box ~ace 33 and external shoulder 17, although they will
contact each other.
In operation the drill pipe members 11 and 13 are
made-up to a torque that pro~ides pressure equal to about
one-half the yield strengths o~ the pin base 21 and box
I ~ ~ 2 ~
counterbore section 37. The yield strength is the pressure,
either compression or tension, at which either the pin base 21
or the box counterbore section 37 will permanently deform~
As tor~ue is applied, counter~ore sectlon 37 compresses and
5 pin base 21 lengthens, resultin~ in the pin face 29 advancing
downward. At make-up torque, pin face 29 will be spaced
closely to, or possibly even in contact with the internal
shoulder 43. However any pressure at internal shoulder 43
is less than at external shoulder 17 at make~up.
The drill pipe members are then lowered into the well
and rotated or drilling. During drilling, additional torque
might be encountered if the drill bit or structure on the
lower end of the drill string becomes stuck. Further
compression of counterbore section 37 and lengthening of pin
15 base 21 b" the additional torque will cause the pin face 29
to press against the internal shoulder 43 and make-up tightly.
Ideally, t:he dimensions are such that the yield strength of
the nose section 27 will be reached approximately the same
time or no later than the time at which the cumulative yield
20 strengths of the pin base section 21 and box counterbore
section 37 are reached. The additional pressure exerted by
the pin face 29 against the internal shoulder 43 increases
the amount of torque required to yleld the tool joint
considerably.
The base section 21, countexbore section 37 and nose
section 27 serve as spring means for causing the box face 33
to tighten against external shoulder 17 to a pressure at
make-up torque in excess of the pressure, if any, that pin
face 29 imposes against internal shoulder 43. The lengths
30 are selected to provide sufficient spring to allow deflection
of these members and result in the ma3~e~up of the internal
shoulder 43 if additional torque is encountered during
drilling. To explain how these dimensions are determined,
an actual example for modification of an A.P.I. (American
35 Petroleum Institute~ standard 3 1/2 inch I~Fo tool joint
~AIill be discussed. First, the ~ores 47 and 49 are
o
--6--
standard diameter bores for this size of tool joint, this
dimension being 2.688 inch, The outer diameter of base
section 21 is selected to be 3.668 inch, which is the
minimum outer diameterof a standard tool joint pin at its
last engaged pin thread. This minimum thickness of the base
section 21 is selected to assure that the pin 15 will not
have less strength than a base section of a prior art pin.
The cross-sectional area of the base section 21 calculates
to be 4.892 square inches.
To assure that the counterbore section 37 dGes not
fail substantially earlier than the pin base section 21,
the cross-sectional area of the counterbore section 37 is
selected to be substantially the same as that of the base
section 21. In the preferred embodiment, to achieve this,
the count~rbore diameter is determined by the standard
counterbore diameter of a tool joint box. The outer diameter
of the recessed area 51 is then calculated to result in the
cross-sectional area of the counterbore section 37 being
substantially the same as that of the pin base section 21.
The recessed area 51 serves to prevent wear on the outer
diameter of counterbore section 37, which might otherwise
reduce the cross-sectional area to below the design amount.
If reduced below the design requirements, the counterbore
section 37 might fail earlier than the base section 21. In
the preferred embodiment, the outer diameter of the recessed
section 51 is 4.813 inch. In the preferred embo~iment, the
inner diameter chosen is 4O073 inch, this resulting in a
cross-sectional area of 5.132 square inches. The difference
in areas of pin base section 21 and counterbore section 37
is .24 square inches, a difference of about 5 percent.
Next, the length of the counterbore section 37 is
selected. This length must be sufficient to provide a
considerable deflection when torque is applied. In the
preferred embodiment, a length of two inches was selected
for the counterbore section 37~ This results in a length
of the base section 21 being slightly greater due to the
engagement of the threads, this becoming 2.19 inch.
The amount of deflection at yield can then be
determined by dividing the yielcl strength for the steel
for this tool joint by Young's ~lodulus, this being 120,000
divided by 28,600,000, resulting in .004 inch per inch.
That is, at the yield stress of 120,000 psi (pounds per
square inch) being exerted on a steel member of this type,
the member will deflect, either in compression or in
tension, .004 inch for each inch of length of the member.
During make-up, the counterbore section 37 will
compress and the base section 21 will elongate. At a
torque that results in one-half the yield strength, 60,000
psi ~pouncls per square inch), the base section 21 elongation
will be 2.19 inch multiplied by .004 inch per inch, and
divided b~ 2, equaling .00438 inch. The counterbore section
37 will compress by an amount equal to two inches in length
times .004 inch per inch divided by two, and multiplied
by the ratio of the cross-sectional area of the base section
21 over the cross-sectional area of the counterbore section
37. This results in a total de~lection at one-half yield
strength of .00381 inch. Consequently, the total relative
motion of the pin face 29 at one-half the yield strength
is the sum of .00433 and .00381 or .00819 inch. At three-
fourth yield strength the deflection is .0122~ inch and atfull yield, the deflection is ~01638 inch.
The dimensions of the nose section 27 are selected by
choosing a length that will cause the nose section to reach
yield strength simultaneously or slightly sooner than the
pin base section 21 and counterbore section 37. To avoid
making the length longer than necessary, a criteria that
the pin face 29 contact initially internal shoulder 43 only
at three-fourth yield was chosen. At this point, pin base
section 21 and counterbore section 37 will have moved pin
face 29 down~ard .01228 inch. To reach full yield, pin
base section 21 and counterbore section 23 must deflect an
additional .00409 inch. Nose section 29 will compress
.00~09 inch because of this deflection. The length of nose
section 29 is selected to reach full yield when compressed
.00409 inch. We previously noted that deflection of this
type of steel is the yield strength over Young's Modulus or
.004 inch per inch. Since approximately .004 inch of com-
pression is needed in nose section 29 to reach full yield
simultaneously with pin base section 21 and counterbore
section 37, the len~th of nose section 29 should be one inch.
For the outer diameter of nose section 29, the threads
25 and 39 were truncated as much as possible without reducing
their strength. The selected length is about 2 3/8 inches.
A diameter slightly less than the minimum outer diameter
at the truncated end of the threads was selected to be the
outer dia~eter of nose section 27, which in the preferred
embodiment is 3.188 inch.
The next dimension to determine is the positioning
of the in1:ernal shoulder 43. A criteria in the design is
that at full make-up torque, which is one-half yield
strength at external shoulder 17, the pin ~ace 29 will
exert little i~ any pressure against the internal shoulder 43.
We have previously determined that pin face 29 will move
downward .00319 inch at full make-up torque and one-half
yield strength. A clearance of .012 inch between pin face
29 and internal shoulder k3 at hand tight would thus reduce
to about .004 inch at full ma~e-up torque because oE the
.00819 inch movement due to the deflection of pin base section
21 and counterbore section 37. Additional torque encoun-tered
up to three-fourths of the yield at the external shoulder 17
would result in a de~lection of pin base section 21 and
counterbore section 37 of an additional ~00~09 inch. ~his
places the pin face 29 initially in contact with the internal
shoulder 43 at three-fourth yield. Additional torque from
three fourths yield to full yield would cause the pin face 29,
if unrestrained, to mo~e downward an additional .30409 inch.
However, since the pin ~ace 29 contacted the internal shoulder
~ ~2`~`YO
43 at three-fourth yield strength, the nose section 27 will
compress for .00409 inch. This is the amount of deflection
that the nose section 27 undergoes at full yield. This
results in the nose section 27 reaching full yield
simultaneously with the pin base section 21 and counterbore
section 37.
To achieve the desirecl yap between pin face 29 and
internal shoulder 43 at hand tight of .012 inch, the distance
from the box face 33 to the internal shoulder 43 is selected
to be .012 inch greater than the distance from the pin
shoulder 17 to the pin face 29, or 5.742 inch. While this
is the ideal dimension, a reaslistic manufacturing tolerance
for these dimensions is plus 0 and minus .005 inch from the
total dimensions of 5.730 and 5.742 inches. This results
in a hard tight gap between pin face 29 and internal shoulder
43 of a minimum of .007 inch and an ideal maximum of .012 inch.
If a tool joint has a minimum gap rather than the ideal gap,
the nose section 27 will yield before the pin base section 21
or counterbore section 37 yields. ~lsof at full make-up
torque, pin face 29 will exert some compression against
internal shoulder 43. This occurs because with a total
defleetion frGm hand tight to half yield of .00819 inch, a
minimum hand tight gap of .007 inch will place the nose
section 27 under .001 inch compression. A deflection of
.001 inch places nose section 27 at one-fourth yield,
while pin base section 21 and counterbore section 37 will
be at one-half yield. Nose section 27 will reach its full
yield strength at a compression of .004 inch. Increasing
the torque from one-half yield to three-fourth yield of
pin base section 21 and counterbore section 37 causes
.00409 deflection of these members. Consequently, the
nose section 27 will reaeh full yield slightly before the
base section 21 and counterbore section 37 reach three-fourth
yield. This might result in cracking of the nose section 27,
however, this will be less detrimental than cracking occurring
in the base section 21 or counterbore section 37. Cracking of
2 ~
--10--
the nose section 27 will not result in parting of the drill
string. Up to, and beyond the point at which the nose section
27 yields, it does provide additional torque withstanding
abilities.
Through standard calculations, the torque to yield
pin base section 21 or counterbore section 37 on the above
described tool joint at the ideal dimensions is 25,583 foot
pounds. A conventional tool joint having a five inch outer
diameter and ~ 11/16 inner diameter, as does this tool join-t,
has a torque withstanding ability of only 18,100 ~oot pounds
at full yield. This increase in torque required to yield
a tool joint furthex reduces the chances for parting of the
drill string while drilling. The increase in the strength
of the tool joint is accomplished without additional metal5 thicknesses or higher steel strengths.
h'hile the invention has been shown in only one of its
forms, it should be apparent to those skilled in the art that
it is not so limited but is susceptible to various changes
and modifications without departing from -the scope of the
invention.
