Method of and apparatus for making up a threaded connection

A method of and apparatus for making up two members having mating threaded connections, such as pipe joints or bolts, for insuring that a specified number of threads have been engaged and a specific torque has been applied. The mating threaded connections are threadably engaged while measurements are made of the torque required to turn one of the members relative to the other, and measurements are made of the number of turns of the members relative to each other. In order to insure that a bad joint is not made up, the measurements of torque and turns must remain within specified parameters or the threaded interconnection is discontinued. The method and apparatus further includes avoiding erroneous turn measurements that may occur such as due to bending or swaying of one of the members during makeup.

BACKGROUND OF THE INVENTION 
It is well known that in order to satisfactorily make up a threaded 
connection between two members having mating threads, such as oil field 
tubing and casing joints or bolts, that a specified number of threads have 
to be engaged and a specific torque applied, particularly in the case of 
tubular goods which are required to be leak proof. Prior U.S. Pat. Nos. 
3,368,396; 3,606,664; 3,745,820 illustrate apparatus for measuring torque 
and counting the number of turns a threaded connection is engaged. 
However, the prior art devices only indicate that a "bad joint" has been 
made up when certain predetermined conditions are found to exist. It is 
desired that failure in a made-up joint be predicted and detected as soon 
as possible so that additional damage to the threads does not occur and 
also to avoid the continual application of torque to defective joints 
because it is very difficult and time-consuming to uncouple defective 
threaded connections. 
Generally, when a threaded connection begins to interengage, more torque is 
required to rotate one of the members relative to the other member. When 
the applied torque reaches a predetermined point, it is referred to as 
reference torque and is the starting point for counting the number of 
turns of one member relative to the other for measuring engagement of the 
threads. However, it has been found that during actual makeup of the 
threaded connection, bending of one of the threaded members relative to 
the other threaded member, such as occurs on a drilling rig when rotating 
pipe sways, creates a false indication of reference torque during initial 
makeup before proper actual thread makeup is started. With the prior art 
devices, any time torque was exceeded, turn counts were measured with the 
counts discontinuing when torque fell below reference torque. The false 
turns were included as a portion of the final turns producing an error 
that resulted in insufficient actual thread makeup. However, the present 
invention overcomes the problem of erroneous turn count by utilizing the 
fact that when the torque drops below reference torque the turns 
introduced, while the torque, was above reference torque are removed. When 
torque is maintained above reference torque number of turns are 
accumulated. 
SUMMARY 
The present invention is directed to a method of and apparatus for making 
up a threaded connection of two members having mating threads by 
monitoring the makeup as it proceeds and predicting failure of the joint 
before the end point of the makeup is reached thereby avoiding damage to 
the threaded connection. The threaded turns and the applied torque are 
continuously measured during the makeup and if the torque/turn 
relationship does not proceed within certain specified parameters, the 
makeup is discontinued. 
A further object of the present invention is the provision of a method and 
apparatus for avoiding erroneous measurement of turns of the makeup of the 
mating threads by counting the turns if the measured torque exceeds a 
reference torque value, but if the measured torque drops below the 
reference torque, then all measured turns accumulated are automatically 
erased and when the torque again exceeds the reference torque value, a new 
measurement of turns will be made. This particular feature will avoid 
errors in turn counts caused by deflection of one of the threaded members 
relative to the other threaded member during initial makeup. 
Yet a still further object of the present invention is the provision of a 
method of and an apparatus for making up two members having mating threads 
by threadably interengaging said mating threads while measuring the torque 
required to turn one of the members relative to the other member until a 
predetermined reference torque is reached. Thereafter further threadably 
interengaging the mating threads and counting the number of turns of one 
member relative to the other while continuing to measure the torque, but 
discontinuing the further threaded interengagement of the mating threads 
when the torque required to further threadably engage the mating threads 
is greater than 
##EQU1## 
or is less than 
##EQU2## 
where N is the number of threaded turns. 
Still a further object is the provision of a method and apparatus of 
continuously monitoring the makeup of a threaded connection from the 
reference torque point to the end of a successful makeup, but stopping the 
progress of the makeup anytime the relationship between the measured 
torque and measured turns exceeds predetermined values. 
Other and further objects, features and advantages will be apparent from 
the following description of a presently preferred embodiment of the 
invention, given for the purpose of disclosure and taken in conjunction 
with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
While the present invention is applicable to making up threaded connections 
such as bolt and stud connections, for purposes of illustration only, it 
will be described in connection with joining one length of tubular goods, 
such as a well pipe, to another. 
Referring now to the drawings, power tongs, generally indicated by the 
reference numeral 10, include a rotatable jaw member 12 for gripping and 
rotating a well pipe string section, such as pipe section 14. The lower 
end of pipe section 14 is shown being threaded into a pipe coupling 16 to 
which is also threaded the upper end of a second pipe section 18. A tong 
prime mover 20, such as a hydraulic motor, is connected to the rotatable 
jaw member 12 by a drive mechanism (not shown) in a conventional manner. A 
supply line 22, provided with a valve 24, is connected to the hydraulic 
motor 20 for supplying actuating power to the motor 24. An energizing 
relay 26 actuates the valve 24. Any suitable apparatus for measuring the 
torque exerted by the rotary jaw member 12 on the well pipe 14 may be 
utilized. For example, an electric strain gauge 30 may be incorporated in 
a backup line 33 connected to the power tongs 10 which provide an 
electrical signal indicative of the torque exerted by the rotary jaw 
member 12, which torque is proportional to the strain in the backup line 
33. 
Suitable means are provided for measuring the rotation of the rotatable jaw 
member 12 and thus of the pipe section 14. For example, the rotary jaw 
member 14 may be provided with a number of lugs or projections 32 which in 
turn actuates a microswitch 34 having an actuating arm 36 so that the 
projections 32 will successfully engage actuating arm 36 to momentarily 
close microswitch 34 as the rotatable jaw member 12 is driven by the motor 
20. The result is that a series of pulses or counts will be transmitted 
through line 38. Therefore, the thread makeup of the pipe section 14 
relative to the coupling 16 (if the coupling is stationary) may be 
measured by counting the number of switch closures as the pipe 14 rotates. 
Normally, the lugs 32 actuate the switch 34 ten times per one revolution 
of the pipe 14. 
Of course, if the coupling 16 is already tightly threaded to the pipe 
section 18, then the only concern is to make up a satisfactory fluid-tight 
joint between the pipe section 14 and the coupling 16. However, if the 
coupling 16 is merely floated onto the pipe section 18, then the power 
tongs 10 will provide a double end makeup. That is, the tongs 10 will make 
up the threaded connection between the pipe 14 and coupling 16 as well as 
between the coupling 16 and the pipe section 18. In the case of a double 
end makeup, the number of turns of rotation of the pipe coupling 16 must 
also be measured. For example, a bottom wheel 40 is provided which 
frictionally engages and rides on the outer surface of the coupling 16 
whereby the rotation of the coupling 16 causes wheel 40 and a connecting 
actuator wheel 42 mounted on a common shaft with the wheel 40 to rotate. A 
number of lugs or projections 44 are provided on the actuator wheel 42 so 
as to engage actuating arm 45 of a second microswitch 46. Microswitch 46 
provides a series of pulses or counts to line 48 to provide an indication 
of the rotation turns of coupling 16. 
The output from the strain gauge 30, which is a measure of the torque 
applied by the tongs 10 to the pipe section 14 is measured by lines 50 and 
52, converted to voltage in converter 54, transmitted to a slope 
conversion subsystem 56 and further transmitted to the microprocessor 60 
which includes a ROM 62 (read only memory) and a RAM 64 (random access 
memory). 
The turns count of the top pipe section 14 is transmitted over line 38 to 
the microprocessor 60 and the turns count of the bottom coupling member 16 
is transmitted over line 48 to the microprocessor 60. A reset switch 66 is 
provided to reset the system prior to threadably connecting each pair of 
threaded connections. 
A control panel 68 is provided on which various values are preset, 
depending upon the type of makeup being connected such as specific size, 
weight, grade and type of pipe connection. Thumbwheel switches 70, 72 and 
74 are provided for setting in the values of low turns, minimum turns, and 
maximum turns, respectively. Thumbwheel switches 76, 78 and 80 are 
provided for inserting values of maximum torque, minimum torque and 
reference torque into the system. Various manually actuated switches, 
which will be described in greater detail, such as an automatic turn 
correction switch 82, an automatic-manual switch 84, and a single-double 
makeup switch 86 are provided to set the mode of operation of the system. 
Various displays are provided to provide the operator with instantaneous 
values concerning the number of turns and applied torque as the makeup 
progresses. Thus, display 88 provides a readout of the turns of top member 
14, display 90 provides a readout of the number of turns of the bottom 
member 16, display 92 provides a readout of the torque applied by the 
power tongs 10, and readout 94 provides a hold readout indicating the 
maximum torque applied by the tongs 10 to a makeup. A recorder 96 is 
provided which may be a strip chart device for recording both the applied 
torque in turns and the values set into the system thereby providing a 
record of the makeup of each joint. The inlet-outlet port 98 provides an 
interface between the processor 60 and the control panel 68 and recorder 
96. Indicator lights 95 and 97 indicate whether the joint being made up is 
good or bad, respectively, and a horn 91 and a siren 93 are provided to 
give an audible signal of whether a makeup is good or bad, respectively. 
It is generally known that if a specified number of threads is engaged and 
a specified torque is applied, together with proper cleaning and 
application of specific pipe dope compounds, then a threaded connection 
will be leak proof. Referring now to FIG. 2, a chart is shown of torque 
versus applied turns for a particular pipe, namely, 41/2inch API-NU, 12.6 
pounds, grade J-55 casing. If the measured torque and measured turns fall 
within the square 100 at the end of a makeup, then the connection is 
generally considered a good joint. The square 100 is bounded by a minimum 
torque rating 102, a maximum torque rating 104, a minimum turn 106 and a 
maximum turn 108. However, if the torque and turn measurement fall outside 
of the square 100 at the end of the makeup, then the threaded connection 
is considered a bad joint. 
As one member of a threaded connection is being made up, that is, 
connecting one member to another member, one member such as pipe section 
14 is rotated relative to the other member such as coupling 16. As the 
coacting threads between pipe section 14 and coupling 16 begin to engage, 
more torque is required to rotate the pipe 14. When the applied torque 
reaches a predetermined point, it is referred to as reference torque 110 
and is the starting point for beginning the measurement of the turn counts 
of the rotation of the pipe. When a threaded connection is being made up, 
there are relationships that exist between the applied torque, and the 
number of threads being engaged. If proper doping procedure is used, then 
the relationship between the applied torque and the turns being engaged is 
predictable (assuming that the threads are not damaged) from the reference 
torque point 112 to a seal tight point, the end of a successful makeup, in 
the good joint area 100. In the past, no consideration was given to this 
relationship until the end point of makeup was reached, and, at that 
point, the threaded connection would be determined to be either a good 
joint or a bad joint. For example, it would be considered a bad joint if 
the torque was excessive with insufficient threads engaged or if an 
excessive number of turns were applied. 
If the makeup process continues along the line 114 with the torque/turns 
relationship indicated, this would indicate an ideal type makeup and a 
good joint. 
However, it is desirous that any prospective failure mode be detected as 
soon as possible so that additional damage to the coupling 16 or pipes 14 
or 18 would not occur. As an example, if the coupling 16 contains a 
defective thread, then a continued application of torque could cause 
damage to the coacting threads. Another disadvantage to continued 
application of torque is, that excessive damage to the threads makes it 
very difficult and time-consuming to uncouple the defective components, 
resulting in lost time. 
The present invention is directed to a method and apparatus whereby the 
turns count is compared to the applied measured torque as soon as the 
reference torque 110 occurs, and the results during the continued makeup 
of the threaded connection must be within certain specified parameters or 
the makeup is discontinued. That is, the present apparatus and method is 
directed to predicting the occurrence of a bad joint without waiting until 
the end of the joint makeup. 
The parameter control portion of this invention relates to maximum and 
minimum slopes established. During makeup, the actual slope of 
torque/turns must continually stay within the boundaries or it is 
predicted either a mechanical or leakage problem will be encountered. 
Referring to FIG. 2, the maximum allowable slope 116 is designated "M. 
max." and reflects equation 1. The minimum slope 118 is labeled "M. min." 
and reflects equation 2. 
##EQU3## 
where: Min. Torque Set = Value derived by certain stress calculations, and 
proven in field test, for each grade, type and size of pipe. 
Max. Torque Set = 120 - 200% Min. Torque Set 
Ref. Torque Set = 10% Min. Torque Set (hand tight) 
Min. Turns Set = Value derived by certain stress calculations and proven in 
field test, for each grade, type and size of pipe. 
Max. Turn Set = 120 - 200% of Min. Turns Set 
Low Turns Set = 25% of Min. Turns Set 
It should be noted that variable percentages of minimum torque can be used 
as well as variable percentages of minimum turns can be used for the other 
set points. 
The three torque settings (reference torque 120, minimum torque 102, and 
maximum torque 104), and the three turns settings (low turns 122, minimum 
turns 106, and maximum turns 108) are entered by the operator into digital 
thumbwheel switches 80, 78, 76, 70, 72 and 74, respectively, located on 
the control panel 68 (FIG. 1). The "set" values are supplied to the 
operator in booklet form for each type, grade and size of pipe. 
When the processor 60 is energized, the set points are introduced to the 
electric circuits, and the value of "M min." and "M max." are placed in 
memory. 
When makeup commences and threads are engaged, torque requirements increase 
until strain gauge 30 detects a "hand tight" condition (reference torque 
110). 
When reference torque point 112 is reached, count pulses normally 
representing 0.1 or 0.01% of a turn per pulse are introduced into the 
processor 60, or other factors of a turn can be used dependent upon the 
count pickup means. When an amount of pulses representing "low turns" 106 
is reached, all parameter circuits are energized, and two equations are 
calculated. 
High Acceptance (HA) = N(M. max.) + Ref. Torque 
Low Acceptance (LA) = N(M. min.) + Ref. Torque 
Actual Value (AV) = Torque 
where: 
N = No. of Turns in 0.1 or 0.01 turns increments (or other incremental 
turns used) 
Torque = Measured torque, in ft. lbs. 
If AV is less than HA, and greater than LA, then the joint is forecast to 
be a good joint. However, if AV is greater than HA, or less than LA, the 
joint is forecast to be a bad joint. 
Certain defects can exist before the low turns point is reached. Defective 
threads can cause excessive torque before low turns are reached. In this 
case, if min. torque 102 is reached before low turns 122, then the joint 
is forecast to be a bad joint. 
To better understand this invention, assume a type and grade of pipe is 
selected. The torque and turns settings for producing a leak proof 
connection are furnished. 
Pipe--41/2 inch API-NU, 12.6 LBS., Grade J - 55 Casing 
The Data Book Shows 
Min. Torque Set = 1500 ft. lbs. 
Min. Turns Set = 1.4 Turns 
Ref. Torque Set = 150 ft. lbs. 
Max. Torque Set = 3000 ft. lbs. 
Max. Turns Set = 4.2 Turns 
Low Turns Set = 0.4 Turns 
The above set points are entered via thumbwheel switches 70, 72, 74, 76, 78 
and 80 into the control panel 68. 
The processor 60 is energized, makeup commences and the threads are 
engaged. Assume reference torque 110 is reached, and the count pulses 
starts. When the turns count reaches low turns 122 set (in this case 0.4 
turns) assume torque = 540 ft. lbs. This torque value is then 
electronically compared to HA: 
##EQU4## 
Since the torque (AV) = 540 the M. max. has not been exceeded. 
Compare AV to LA 
##EQU5## 
Since AV = 540, then M. min. has not been exceeded. 
The makeup is proceeding within the max. and min. boundaries, and is 
predicted to be a successful makeup. 
If the torque value at 0.4 turn was 1100 ft. lbs., the M. max. 116 would be 
exceeded. If the torque value at 0.4 turns was 220 ft. lbs., then M. min. 
118 would be exceeded, and in both cases, a bad joint alarm would be 
activated. 
By referring to FIG. 2, it may be seen that as long as the torque value 
stays within the Max./Min. values 116 and 118, the end result will be a 
successful connection. 
However, in prior art systems, it has been found that during actual makeup 
of the pipe section 14 to a pipe coupling 16, swaying of the rotating pipe 
section 14 created false indications of torque during initial makeup, and 
reference torque was reached before actual thread makeup was started. It 
was also noted that the reference torque, which was erroneously surpassed, 
dropped below reference torque in unison with the sway. Therefore, by 
measuring the turn counts based upon when reference torque was exceeded, 
an error was produced in measuring a turn count and sufficient thread 
makeup was not reached. Another feature of the present invention is the 
provision of automatic means to remove false turn counts. Therefore, the 
microprocessor 60 monitors the turns input signals, and if the measured 
torque exceeds the reference torque, it allows the turn count pulses to be 
accepted. However, if the measured torque drops below the reference torque 
110 anytime, for any reason, before the minimum torque 102 point is 
reached, then all of the turn counts accumulated are automatically erased 
from the storage bank. When the measured torque again exceeds the 
reference torque 110, new turn counts will be received. 
Referring now to FIGS. 3A, 3B and 3C, the control programs stored in the 
microprocessor 60 is best seen. Preferably, the microprocessor may be an 
RCA microprocessor model 1802. In step P1, the main program control is set 
to register one, in step P2, the entire system is reset, in step P3, RAM 
62 is zeroed and the work registers are set. In step P4, the input data 
which is set in the hand switches 70, 72, 74, 76, 78 and 80 which includes 
reference torque, minimum torque, maximum torque, low turns, minimum 
turns, and maximum turns, are received. In step P5, the input data 
received in step P4, which is in binary coded decimal form, is converted 
to binary form and then in step P6 are stored in the RAM 64 for future 
tests. 
In step P7, all received data is checked to determine if it is defective, 
and if so, the processor proceeds to step P8 and P9 and recycled and 
provides an indication of a bad joint to indicate a defect in the received 
data. On the other hand, if in step P7 the data received is numeric, the 
processor continues to step P10 by zeroing and blanking the displayed 
digits in displays 88, 90, 92 and 94. In step 11, the automatic testing is 
prepared for programming. Panel input switches 82, 84 and 86 have been 
manually actuated to indicate whether the automatic turns correction 
feature is to be used (ATC), whether the thread makeup is to be 
automatically terminated upon the indication of a failure prediction or 
merely sound an alarm (auto-manual), or to indicate whether or not a 
single threaded connection is to be made up, such as a threaded connection 
between pipe section 14 and the pipe coupling 16, or if a double threaded 
connection is to be made up between the pipe section 14, the coupling 16, 
and the lower pipe section 18 (single-double). The information from 
switches 82, 84 and 86 is then stored in RAM 64 which determines the mode 
of operation. Step P3 sets the displays and if good flag is off and bad 
flag is off, then display the last torque and turn values on the displays 
88, 90, 82 and 94. 
In step P14, if the measured torque is above or greater than the said 
reference torque, the set turns of the top and bottom counters are enabled 
in step P15 or otherwise the flag for clear turns is enabled. 
If the measured torque is below reference torque and the reset switch 66 is 
off, the program is recycled. If the measured torque is below reference 
torque and the reset switch 66 is on, the program starts again at step P1. 
If the measured torque is below the reference torque and the turns 
correction switch 82 is enabled, then any accumulated measured turns are 
zeroed. If the measured torque is greater than the reference torque, the 
turns accumulation in step P15 is actuated and step P16 is actuated to 
start the recorder 96. 
In steps P17, P18, P19, P20 and P21, the binary torque measurements, the 
binary top count measurement, and the binary bottom count measurement are 
converted to binary coded decimal display measurements and displayed in 
displays 88, 90, 92 and 94. In step P22, the measured torque is compared 
with the maximum set torque to determine if the measured torque is greater 
than the maximum torque, and if so, step P23 indicates this on display 94 
and in step P24 turns the top and bottom counts and the recorder off. 
Steps P25, P26, P27 and P28 relate to automatically correcting the turns 
count whenever the measured torque is less than the reference torque by 
zeroing the top and bottom measured count. 
In steps P29, P30 and P31, if the measured torque is less than the 
reference torque, the program is recycled to step P2. However, if the 
measured torque is greater than the reference torque, the program 
continues to step P33 which is controlled by the auto-manual switch 84. 
When the manual switch is actuated the following test will only provide a 
visual and audible indication to the operator who then manually controls 
the continuation or stopping of the threaded makeup. If the auto position 
is selected, the following test will continue to automatically make up the 
joint or stop the makeup automatically depending upon the test results. 
Step P34 compares the measured top and bottom counts with the set low turns 
to determine when the low turns parameter has been reached. Steps P35 
through 44, test the measured torque and measured turn counts to insure 
that they are within the control parameters. A bad flag is indicated in 
the RAM 64, the bad lamp 97 and siren 93 are turned on, and the bypass 
valve 24 is actuated to stop the joint makeup when the following 
indications occur: 
If the measured torque is less than 
##EQU6## 
If measured torque is less than 
##EQU7## 
If measured torque is greater than 
##EQU8## 
If measured torque is greater than 
##EQU9## 
If measured torque is greater than the minimum torque and either the top 
turns is less than low top turns or bottom turns is less than low bottom 
turns, 
If either bottom measured turns are greater than maximum bottom turns or 
measured top turns are greater than maximum top turns, 
If measured torque is greater than maximum torque. 
On the other hand, if the measured torque is less than minimum torque and 
the top measured turns are less than minimum top turns and the bottom 
measured turns are less than the minimum bottom turns, this is an 
indication that the threaded makeup is progressing satisfactorily, a good 
flag is set and the program recycles to step P14. 
Assuming that the threading of the joint proceeds satisfactorily and does 
not indicate a failure, a good test condition will be indicated, the green 
light 95 and horn 91 will be indicated and the bypass valve 24 will be 
actuated to stop the joint makeup when the measured torque is greater than 
the minimum torque and both the measured bottom turns are greater than the 
minimum bottom turns and the measured top turns are greater than the 
minimum top turns. A print command is given to the recorder 96 to record 
and save all of the data set in the switches 70, 72, 74, 76, 78 and 80 and 
in the displays 88, 90, 92 and 94. 
The present invention, therefore, is well adapted to carry out the objects 
and attain the ends and advantages mentioned as well as other inherent 
therein. While a presently preferred embodiment of the invention is given 
for the purpose of disclosure, numerous changes in the details of 
construction, arrangement of parts, and steps of the process will readily 
suggest themselves to those skilled in the art and which are encompassed 
within the spirit of the invention and the scope of the appended claims.