torque vs tension interpretation instructions rev 6

7/27/2019 Torque vs Tension Interpretation Instructions Rev 6

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Torque vs. Tension Interpretation Instructions

The enclosed 2008 raise drill Steel Torque-Tension charts are the latest edition from Mining

Technologies International of Sudbury, Ontario, Canada.

The DI-22 threaded raise drill steel was originated by Drilco Industrial of Midland, Texas in

1965. However, it was not until 1975 that Drilco introduced the first torque tension charts to aidin the application and use of the steel. In that 10 year period, with the exception of the 12-7/8

steel with 10-1/8 DI-42 connections, most of the current steel sizes were produced and put into

service. As a result, the Torque-Tension charts did not have the significance that they should

have had. A lack of instruction and understanding in how to apply the charts also presented a

problem in the use of the charts. To add to the confusion, in the following years, other suppliers

of drill steel entered the market without a background in the market and proceeded to publish

charts without the required engineering and metallurgical knowledge to define properly the

operational limits of the system. As a result, for all present applications, users have relied mostly

on their own operational experience to set their operating parameters, with reasonable success.

Now, with the need for longer and larger diameter raises requiring up-rated machines and drill

steel, it is necessary to review the form, construction and interpretation of the Torque-Tension

charts in the light of 40 years of experience.

In reviewing in detail a number of published Torque-Tension charts since the origination of the1975 charts, it is obvious that the original Drilco charts are more correct that any others

published after 1975. The major discrepancy in the original charts was a failure to understand and

explain how to use the charts properly. The most important fact to understand about the charts is

the concept of initial makeup torque, because the initial makeup torque controls the capacity of

the drill steel to handle safely the drilling loads applied to the reamer.

The Torque-Tension chart is a visual plot of the equation developed by A.P. Farr of Hughes Tool

in 1957, based upon the Screw Jack principle, as shown in the enclosed illustration, andapplied to a rotary shouldered connection. It is theoretical, but the values indicated on the latest

Torque-Tension chart format, show de-rated operational levels that we consider to be safe for

reasonable life of the connection fully described on each chart. It is important to understand that

each MTI chart describes only MTI produced connections represented by that chart and that it not

be indiscriminately applied to other suppliers products


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Farrs formula, for Torque only, addresses, in its most basic form, what occurs when a box and

pin are screwed together to produce a load on the joint shoulders. Assume a connection, with the

box critical area for torque equal to the pin critical area for torque, and that a torque is applied,

until the material yield stress in the critical areas of the box and pin is reached. The connection is

now pre-loaded with the maximum load possible on the threads and shoulders. We now can

apply an external torque load that can vary from zero to maximum without affecting the joint.

However, there is a need also to apply an external tension load. Because of the shoulder load, wecan do this. But, as the tension load is applied, the internal joint loads are affected. The shoulder

loads are reduced as tension is applied up to the maximum value of the shoulder pre-load from

pre-torque. As the shoulder loads are reduced by the external tension, any external torque load

applied must be reduced accordingly. This fact is defined on the Torque-Tension diagram by the

right hand sloping line.

The shoulder separation zone, shown on the chart, is derived by looking at the joint merely

screwed together with the shoulders in contact, but without load. As external tension is applied,

the pin will stretch up to the material yield point. To keep the shoulders together, but unloaded,

will require an external torque to be applied to the joint as external tension is applied. This zone

is defined on the Torque-Tension diagram by the phantom shoulder separation line from the zero

torque and tension axes to the maximum tension-torque point which is coincident with the

maximum Torque-Tension point of the right hand torque plus tension line. This zone is only of

value for fishing purposes and to define the limits of subsequent torque plus tension lines. The

other sloping lines reflect the effects of box O.D. wear which limits initial makeup torque.

As shown on the diagram, the operating zone with initial makeup torque is defined by the sloping

lines and the tension line drawn over to the left to the tension axis from the intersection of each

sloping line with the phantom shoulder separation line. It is especially important to understand

that the pre-torque (initial makeup torque) determines the safe allowable operating torque and

tension. With that in mind, it is time to see how to use the Torque-Tension chart. There are two

ways to use the charts - I) from an operators viewpoint; II) from an engineers or planners

viewpoint.

I) Torque-Tension operators viewpoint

From an operators viewpoint the new Torque Tension charts can be used very readily to set


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Proceed as follows, using above information:

A. Select proper Torque-Tension chart, using d) above

B. Use the following sketch as a guide to interpret the selected Torque-Tension chart.

C. On the sketch, 1), 2), 3) represent the drill steel maximum operation line on the

selected Torque-Tension chart.

D. Lines 4 through 9 on the sketch represent the machine reaming thrust and torque to

be plotted onto the selected Torque-Tension chart. Follow the arrows in the orderindicated to arrive at the required machine makeup torque required, # 10.

ENS.

0

8

5

9

6

10 2

74

1

TORQ.

3

1) Maximum drill steel tension (.6 yield) on Torque-Tension chart

2) Maximum drill steel initial makeup torque (.6 yield) on Torque-Tension chart

3) Maximum drill steel operating Torque +Tension with initial makeup torque (2)

4) & 5) Machine rated reaming thrust

6) & 7) M hi d i


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Interpretation of Chart Plot

1. If line 9) plots to the right of line 3) the machine has more power than the drill steel

can with stand. Then machine setting must be adjusted to line 3) levels, if the drill

steel O.D. is to new diameter. On the Torque-Tension chart, there are 4 operating

levels indicated, which indicate reduced operating levels for various diameters

corresponding to wear diameters of the steel. Always select the makeup torqueaccording to steel diameter. The 70% line is shown to be the minimum recommended

makeup torque. The reason for this recommendation is that this wear diameter has

been considered to be the time to replace the steel. It is important to understand that,

regardless of steel diameter. The initial makeup torque defines the chart location of

line 9) and thus determines the limit of operation. For instance, if the makeup torque

at 70% is used with new drill steel, the operating zone line 9) is still the limit of

operation, and not line 3).

2. If line 9) plots to the left of the 70% line, then it is possible that the drill steel is too

large for the rig, unless experience has shown otherwise. In all cases, the operating

limit is always to the left of line 9).

3. If the rig makeup torque is less than 10) on the chart as determined to be necessary in

step 1) and 2) above, then it will be necessary to plot the available makeup torque as

new item 10). Then draw line 9) from 10) parallel to line 3) and this new line 9)

becomes the new maximum operating limit at the new intersection 8).

II) Torque-Tension Engineers or Planners viewpoint

Understanding the Torque-Tension chart provides an engineer or planner with a tool to match a

drilling machine to the proper drill steel to meet the job requirements. The initial parameters

needed are the raise diameter, type of formation, formation hardness, length of hole and hole

angle.

1) The process of evaluation begins with the reamer head. Using the raise diameter andformation information, it is necessary to determine the type cutter required, the number

of cutters, the total cutter load required, and the resultant torque required to rotate the

reamer when properly loaded. The reamer weight is also needed. Normally, this

information is available from the reamer suppliers. If not, the attached tabulation of

generic information can be used for initial estimation The tabulated estimated torque


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string weight. The machine drive head weight must be estimated or obtained from the

drill manufacturer. The drill string weight is primarily a function of the length of hole andcan be calculated by dividing the hole length by the shoulder to shoulder length of an

individual piece of drill steel suitable to the drill. The attached chart lists dimensions and

weights of MTI drill steel. The preliminary total drill string tension (reamer weight +

cutter load + drill steel weight) can be determined.

4) With the preliminary torque and drill string tension determined, select the appropriate

Torque-Tension chart, paying attention to the drill steel material and thread dope

requirements.

5) Plot the torque and pull requirements on the chart and follow the procedures of part I todetermine the required drill steel makeup torque. If any requirements do not match the

drill or the drill steel, the process must be repeated.

6) Most reamer cutters have a maximum allowable peripheral rotational speed of about 300-

350 ft/min. To determine the required reamer rotational speed, divide the 300-350 ft/min

cutter speed by the reamer circumference in feet. To check that the rig drive has sufficient

rotational horsepower, calculate the horsepower by multiplying the reamer torque

required by the reamer rotational speed and divide by 5252.(HP= TN/5252)

MTI Raise Drill Steel Weights

O.D PIN I.D. S/S Length Connection Unit Weight(Inches) (Inches) (Inches) Nomenclature (lbs)

5 3/4 2 13/16 48 4 3/4 DI-22 2056 3/4 4 48 5 3/4 DI-22 225

8 4 3/4 48 6 3/4 DI-22 385

8 4 3/4 60 6 3/4 DI-22 440

10 4 3/4 48 8 1/4 DI-22 600

10 4 3/4 60 8 1/4 DI-22 750

11 1/4 5 7/16 60 9 1/4 DI-22 1000

12 7/8 5 7/16 60 10 1/2 DI-22 & 10 1/8 DI-42 1400

12 7/8 5 7/16 138 10 1/8 DI-42 287013 1/8 4 3/4 138 10 1/2 DI-22 2500

13 1/8 4 3/4 60 10 1/8 DI-42 1520

13 3/8 4 60 10 1/8 DI-42 1645

14 1/8 4 3/4 60 10 7/8 MTI315 1900

14 1/8 4 3/4 84 10 7/8 MTI315 2460

14 1/2 5 7/16 60 11 1/4 MTI315 2020


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#/cutter

k K=10 K=10 K=11.5 K=11.5 K=14 K=1410,000#/cutr 20,000#/cutr 20,000 #/cutr 30,000#/cutr 30,000#/cutr 40,000#/cutr

No. of cutrs Estimated bit load (#) bit load (#) bit load (#) bit load (#) bit load (#) bit load (#)

FT M cutr arms (ft) reamer wt.(#) torque (FT#) torque (FT#) torque (FT#) torque (FT#) torque (FT#) torque (FT#)

8 80,000 160,000 160,000 240,000 240,000 320,000

16.74 16,740 33,480 29,110 43670 35,820 47,830

10 100,000 200,000 200,000 300,000 300,000 400,000

23.28 23,280 46,560 40,490 60,730 49,885 66,51012 120,000 240,000 240,000 360,000 360,000 480,000

30.20 30,200 60,400 52,520 78,780 64,715 86,285

14 140,000 280,000 280,000 420,000 420,000 560,000

38.70 38,700 77,400 67,300 100,960 82,930 110,570

16 160,000 320,000 320,000 480,000 480,000 640,000

57.24 57,240 114,480 99,550 149,320 122,660 163,540

20 200,000 400,000 400,000 600,000 600,000 800,00066.70 66,700 133,400 116,000 174,000 142,930 190,570

24 240,000 480,000 480,000 720,000 720,000 960,000

102.90 102,900 205,800 178,960 268,400 220,500 294,000

26 260,000 520,000 520,000 780,000 780,000 1,040,000

129.68 129,680 259,360 225,530 338,300 277,885 370,510

32 320,000 640,000 640,000 960,000 960,000 1,280,000

179.50 179,500 359,000 312,170 468,260 384,640 512,85038 380,000 760,000 760,000 1,140,000 1,140,000 1,520,000

238.38 238,380 476,760 414,570 621,860 510,810 681,085

40 400,000 800,000 800,000 1,200,000 1,200,000 1,600,000

257.26 257,260 514,520 447,410 671,110 551,270 735,030

42 420,000 840,000 840,000 1,260,000 1,260,000 1,680,000

303.6 303,600 607,200 528,000 792,000 650,570 867,430

26 7.93 44 440,000 880,000 880,000 1,320,000 1,320,000 1,760,000318.0 318,000 636,000 553,040 829,570 681,430 908,570

6

1.52

1.83

UCS 10-20,000 PSI

Bit Dia.

Torque = x (cutter arms)

5

14

16 4.88

4.27

3.04

12 3.66

7 2.13

8 2.43

10

18

20 6.10

5.49

22 6.70

24 7.31

UCS 30-50,000 PSIUCS 20-30,000 PSI

67,000

71,300

80,000

95,000

110,000

125,000

MTI ESTIMATED REAMER OPERATING PARAMETERS

8,900

10,700

12,500

14,300

25,000

57,000

63,000

7


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torque vs tension interpretation instructions rev 6

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