Copyright 2000, IADC/SPE Asia Pacific Drilling Technology

This paper was prepared for presentation at the 2000 IADC/SPE Asia Pacific DrillingTechnology held in Kuala Lumpur, Malaysia 11–13 September 2000.

This paper was selected for presentation by an IADC/SPE Program Committee followingreview of information contained in an abstract submitted by the author(s). Contents of thepaper, as presented, have not been reviewed by the International Association of DrillingContractors or the Society of Petroleum Engineers and are subject to correction by theauthor(s). The material, as presented, does not necessarily reflect any position of the IADC orSPE, their officers, or members. Papers presented at the IADC/SPE meetings are subject topublication review by Editorial Committees of the IADC and SPE. Electronic reproduction,distribution, or storage of any part of this paper for commercial purposes without the writtenconsent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print isrestricted to an abstract of not more than 300 words; illustrations may not be copied. Theabstract must contain conspicuous acknowledgment of where and by whom the paper waspresented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax01-972-952-9435.

AbstractHarsh drilling conditions can exceed the capabilities oftraditional drill string connections. As the petroleum industrymoves toward more severe drilling applications - deepwater,extended reach, high-angle, short-radius and ultra-deep wells -new drill string connection designs are required to safely andefficiently achieve the drilling objectives of these projects.This paper describes three new rotary shoulder connectionsthat provide significant operational advantages for extremedrilling applications.

IntroductionAn advanced, high-performance tool joint design providesapproximately 70% more working torque capacity thanstandard API connections. This new design is a second-generation, double-shoulder connection that is optimized foreach drill pipe size. The connection’s increased torsionalstrength allows for the use of a streamlined tool jointconfiguration. The connections can be configured with asmaller OD and larger ID compared to standard APIconnections without sacrificing torsional capacity.

A second version of this connection incorporates a radialmetal-to-metal internal pressure seal. This connectionprovides high torsional strength combined with gas-tightpressure sealing capability. Drill strings with the gas-tightconnection can be used for drill stem testing (DST) operations,underbalanced drilling and high-pressure workover andcompletion operations. This eliminates the need for a separatework string saving time, money, rig space and set backcapacity. This is a significant advantage in offshoreoperations where rig space and set back capacity are at a

premium.A third development discussed in the paper is a new thread

form that provides increased durability and improved fatiguelife compared to standard API connections. This thread formhas been successfully used on drill pipe pins and drill collarboxes.

This paper discusses the engineering philosophy behindeach of these new designs and details results of physicaltesting. Applications where the connections have been usedare also presented.

Design Configuration and CapabilitiesThe eXtreme Torque (XT ) is a second-generation double-shoulder connection (see Figure 1). The XT design evolvedfrom the design of the HI TORQUE (HT ) connection.

Figure 2 depicts the make-up characteristics of XT andHT. Both connections spin up freely from the stab-in to hand-tight position. In the hand-tight position the primary externalshoulder makes contact. As the connection is made-up fromthe hand-tight to power-tight position the box counterborecompresses and the pin base elongates elastically and thesecondary torque stop engages. The secondary torqueshoulder provides the increased torsional capacity compared toa standard API rotary shoulder connection.

The external (primary) shoulder is the pressure seal for theconnection just as on an API connection. Since the secondaryshoulder functions solely as a torque stop and not a pressureseal, minor damage to the secondary shoulder can be toleratedwithout adversely effecting connection performance providedthere is no protruding metal that will impede contact betweenthe shoulder surfaces. Any protruding metal on the secondaryshoulder must be removed with a file or abrasive paper. Useof thread protectors when the pipe is racked back in thederrick is not required or recommended.

Figure 3 shows a comparison of XT and HT. The threadtaper of the XT connection is flatter than the HT’s to increasethe area of the secondary torque stop, resulting in increasedtorsional capacity. HT provides an approximate 40%improvement in working torque compared to an APIconnection of the same OD and ID dimensions. XT providesapproximately 25% to 30% more working torque capacity thanHT or an improvement in working torque of approximately65% to 70% compared to a standard API connection of the

IADC/SPE 62785

New Developments in Drill Stem Rotary Shoulder ConnectionsMichael J. Jellison, SPE, Grant Prideco; Steve P. Hassmann, SPE, Unocal Thailand, Ltd.; Dong Cotanda Jr., UnocalThailand, Ltd.; Doug Snapp, SPE, Grant Prideco

2 M. J. JELLISON, S. P. HASSMANN, D. COTANDA JR., D. SNAPP IADC/SPE 62785

same dimensions.The shallow thread taper of the XT connection results in

reduced clearance between the pin nose and box face duringstabbing. Consequently, use of a stabbing guide is required toprevent damage to the box face or shoulder that acts as thepressure seal for the connection. With the exception of thestabbing guide requirement, eXtreme Torque handles andmakes-up like a standard API connection. XT spins up freelyuntil shouldered, then is bucked up to the make-up torque.

Incorporating a stabbing guide into the make-up operationdoes not represent a drawback relative to using XT.Experience has shown that once the rig floor personnelbecome familiar and comfortable with the use of the stabbingguide, running times do not suffer and may actually improve.With the stabbing guide, rig personnel place the guide over thebox tool joint and the pin can be stabbed relatively quicklyinto the box. Since the stabbing guide protects the sealingshoulder of the box, the pin does not need to be slowly guidedinto the connection. Care should still be taken during stabbingoperations even with the stabbing guide, but with experience,running speeds may improve somewhat. In addition, runningdamage from mis-stabbing can be reduced or eliminated.

Operational Capabilities. The optimized configuration ofthe new double-shoulder tool joint provides several significantoperational advantages.

High Torsional Strength. As mentioned above, the XTconnection offers significantly higher torsional capacity thanstandard API and HI TORQUE connections. Figure 4 shows acomparison of the maximum make-up torque or workingtorque for API, HT and XT connections for various tool jointssizes. This additional strength provides the required torque forcritical drilling applications.

Streamline Profile. The increased torsional strengthallows for the use of a streamline tool joint that is suitable forthe pipe’s torsional strength. XT connections can beconfigured with a smaller OD and larger ID compared tostandard API connections without sacrificing torsionalcapacity. This can allow a larger drill pipe size to be used forimproved hydraulic performance.

The ability to design more streamlined tool jointconfigurations has permitted the development of severalinnovative drill pipe systems. This new tool joint technologyfacilitated the development of a new product, 5-7/8 in.eXtreme Reach (XR ) drill pipe, that represents enablingtechnology for Extended Reach Drilling (ERD), deep-waterand other deep well applications.1 The hydraulic performanceof the drill string can be a significant limitation in theseapplications resulting in poor hole cleaning, slower penetrationrates, diminished control over well trajectory and drill pipesticking.

The 5-7/8 in. XR drill pipe provides a significantimprovement in hydraulic efficiency compared to 5-1/2 in.drill pipe and does not suffer from the disadvantagesassociated with use of 6-5/8 in. drill pipe.

The eXtreme Torque (XT) connection design, optimizedfor 5-7/8 in. drill pipe, provides exceptional torsional strengthcombined with a streamline configuration. The XT57 tooljoint OD of 7 in. permits fishing of the connection inside of 9-5/8 in. casing or 8-1/2 in. open hole sections with a slim-holeovershot.

An XT54 connection has been designed that permitsfishing of 5-1/2 in. drill pipe inside of 9-5/8 in. casing or 8-1/2in. open hole sections using a full strength overshot. Prior todevelopment of this second generation connection thepractical minimum tool joint OD for 5-1/2 in. drill pipe was 7in., and a slim-hole overshot was required inside of 8-1/2 in.hole sections. The XT54 connection features a 6-3/4 in. ODand 4 in. ID. The 6-3/4 in. OD permits the use of a fullstrength overshot inside 8-1/2 in. hole sections. This increasesthe pull capacity by approximately 80,000 lbf and allows formore intense jarring during fishing operations.

True Flush Inside Diameter. There is no gap or change ininside diameter from the box to the pin, resulting in a recessfree inside bore. This provides a smooth flow conduit withless turbulence. It also eliminates the recess in otherconnections where cement and solids can be trapped.

Damage Resistance. The rugged XT design incorporatesmore steel in the critical areas of the connection resulting inless refacing and fewer recuts.

Increased Wear Tolerance. Because of the increasedtorsional capacity, the connection extends the service life ofthe joint by tolerating more OD wear before the pipe must bedowngraded below Premium Class (Figure 5).

XT can be refaced and a portable refacing tool is alsoavailable to eliminate shipping costs to a machine shop forrepair work and for use in remote areas where machine shopsare not readily accessible.

XT Torsional Testing. Torsional tests have been conductedon several XT configurations. The designs that have beentested are listed below:

• XT31 4 in. x 2 in.

• XT38 4-3/4 in. x 2-9/16 in.

• XT39 4-7/8 in. x 2-9/16 in.

• XT54 6-3/4 in. x 4 in.

• XT57 7 in. x 4-1/4 in.Other sizes were tested during the design and prototypeconstruction process.

Calculations were performed using a form of the APIscrewjack equation that is modified to account for the additionof the secondary torque shoulder at the pin nose.2 Finiteelement analysis (FEA) was also performed on some of thedesign configurations to allow correlation with physical testresults and confirm the calculated torsional strength of theconnection.

The test procedure varied somewhat for the variousconnection configurations evaluated since information inaddition to the torsional strength was desired during sometests. The basic test procedure was 1) measure and record pin

IADC/SPE 62785 NEW DEVELOPMENTS IN DRILL STEM ROTARY SHOULDER CONNECTIONS 3

length and box depth, 2) apply thread compound and 3) make-up the joint until the connection plastically deforms asindicated by a zero slope on the torque/turn curve. Straingages were mounted on the specimens for selected tests toverify the accuracy of the finite element analysis.

Results of the torsional tests are summarized in Table 1.The physical test results combined with the FEA evaluationverified the accuracy of the rating method for the connectionacross the product size range.

XT Field History. Approximately 250,000 ft of drill pipewith the XT advanced double-shoulder connection has beenmanufactured. All of this drill pipe has been in OD sizes 5 in.,5-1/2 in. and 5-7/8 in. Several operators are evaluating XT forupcoming applications on smaller drill pipe sizes. Rentalcompanies own most of the XT drill pipe.

Several XT connection drill strings have been used in thefield. A string of 5-1/2 in. XT55 was the first to be used. Thisdrill string has been rented by four different operators to drillcritical wells in the Gulf of Mexico.

The first string of 5-7/8 in. XR drill pipe went to work fora major operator on a Gulf of Mexico project in July 1999.Two additional strings started jobs in October 1999, and afourth string was put in service in March 2000. The secondand third 5-7/8 in. XR drill strings are being used on deep-water Gulf of Mexico projects operated by two major oilcompanies. The fourth string is being used on a jack-up rigoperated by a major independent in the Gulf of Mexico.

ARCO China Inc. purchased a string of 5-7/8 in. XR drillpipe for their Yacheng ERD project in the South China Sea.Phase 2 of this project began drilling in the second quarter of2000. The project will include two platforms with ERD wellsplanned from both platforms. Wells are planned withhorizontal departures up to 20,000 ft and Measured Depths upto 28,000 ft (approximately 13,500 ft True Vertical Depth).

The improved hydraulic performance of the 5-7/8 in. drillpipe relative to 5-1/2 in. pipe will be extremely beneficial indrilling long 12-1/4 in. hole sections to measured depths inexcess of 21,000 ft.

A drill string made up of 5-1/2 in. XT55 and 5 in. XT50was manufactured earlier this year for a new build deep-waterrig slated for work with a major independent in the Gulf ofMexico.

Gas-Tight Seal OptionA version of the advanced double-shoulder tool jointincorporating a radial metal-to-metal seal has been designedand tested. Designated the XT-M , this connection features ametal-to-metal flank seal with a configuration similar to theseal used in premium tubing and casing connectors (Figure 6).

XT-M is a specialized drill pipe tool joint designed forspecific critical applications. The addition of a gas-tight sealto the connection permits safe, high-pressure drill stem testing(DST) operations using the drill pipe. Consequently, onestring of drill pipe can be used for drilling, workoveroperations and drill stem testing. This eliminates the

requirement for a separate work tubing string on offshorelocations, conserving setback capacity and valuable rig space.

The XT-M connection can also be used in underbalanceddrilling applications to improve the leak resistance of the drillstring. Underbalanced drilling is a growing practice forexploiting hydrocarbon reservoirs. In some underbalancedapplications conventional rotary shoulder tool joints provideless than adequate pressure integrity. XT-M handles andmakes-up like a conventional API rotary shoulder connection,resists galling after multiple make/break cycles and providespressure sealing typical of a premium tubing connection.

XT-M Physical Testing. Two configurations of the XT-Mconnection have been tested. XT-M46 was tested for DST andhigh pressure workstring applications. XT-M39 was tested foruse in underbalanced drilling operations.

Durability and Internal Pressure Testing. A 6-1/4 in. x 3-in. XT-M46 was tested on 4-1/2 in. 20.00 lb/ft S-135 drillpipe. This connection was designed to provide high torsionalstrength, tensile capacity that exceeds the pipe tension rating, agas-tight seal capable of sealing pressures up to 12,500 psicombined with a thread form that resists galling and handlingdamage.3

Prior to testing finite element analysis was conducted todetermine stress levels and verify that suitable dimensions,tolerances and seal interference were utilized in the designconfiguration.

Testing was performed in the field to establish theconnection’s ability to withstand damage from typical rig floorhandling and make-up practices. Laboratory testing wasconducted to establish the leak integrity of the connection withgas. Two sets of pin and box tool joints welded to two jointsof drill pipe were used for make-up and breakout testing.Each joint was made-up and broken out in the vertical positionfor 100 cycles. A make-up torque of 45,000 ft-lbs was used.After completion of the 100 make/break cycles, theconnections were visually inspected and dimensionallygauged. The seal surfaces exhibited normal burnishing andscuffing. The visual and dimensional inspection revealed noexcessive wear, damage or significant galling problems.

Seal integrity tests were conducted with the two sets oftool joints that were used for the make and break testing. By-pass holes were drilled in the pin near the pin nose and in thebox near the box face. These holes by-passed the twoshoulder seals in the connection and permitted isolated testingof the radial metal-to-metal seal configuration. The by-passhole in the box was fitted with a 250C Autoclave connectionto facilitate leak detection through use of a bubble tube. Thespecimens were made-up to 45,000 ft-lbs and placed in apressure test containment pit. Pressure was applied slowly to12,500 psi in approximately 5 minutes using nitrogen gas asthe pressure medium. The 12,500 psi test pressure wasmaintained for thirty minutes while monitoring the bubbletube to determine if any leakage occurred. No leaks weredetected with either sample.

4 M. J. JELLISON, S. P. HASSMANN, D. COTANDA JR., D. SNAPP IADC/SPE 62785

External Pressure Testing. External pressure tests werealso performed using four XT-M39 tool joint samples. Thesamples had 5 in. OD’s and 2-7/16 in. ID’s. The connectionwas evaluated for a 3-1/2 in. drill pipe underbalanced drillingapplication. External pressure was applied using nitrogen gas.This was believed to be the first external pressure testconducted with drill pipe rotary shoulder connections.

Make-up torque for each sample was 22,500 ft-lbs. Eachsample was pressure tested with nitrogen gas as follows:

• 500 psi - 15 minute hold time

• Followed by 5,000 psi - 60 minutes hold time(Note, hold time for sample #1 was 11 hours or 660minutes.)

• followed by 500 psi - 15 minute hold timeSamples #1 and #2 were made-up and broken out 50 times

prior to pressure testing. After make-up testing, by-pass holeswere drilled through the box counterbore and the pin nose ofsample #1 to permit testing of only the metal-to-metal radialseal. Sample #1 held 5,000 psi for 11 hours without leakage.

Two by-pass holes were drilled through the pin nosebehind the metal seal in sample #2 to test the external shoulderseal of this connection. No leakage was recorded during thetest.

Sample #3 was made-up and broken out 100 times andpressure tested. Sample #3 held pressure, and no leakage wasdetected during the test. To evaluate compatibility the sample#3 pin was made-up to sample #4 box, and sample #3 box wasmade-up to sample #4 pin. Both connections remained leaktight for the duration of the external pressure test. No by-passholes were used with samples #3 and #4.

XT-M Field History. A major operator put a string of 4-1/2in. 20.00 lb/ft S-135 XT-M46 in service beginning inSeptember of 1999. The drill string is being used to performworkover, completion and drilling operations on a deep-waterplatform in the Gulf of Mexico. At the time of writing thispaper, the string is still currently in use on the project.

A string of 3-1/2 in. 15.50 lb/ft S-135 XT-M39 will beused by a major operator for underbalanced drilling operationsin the North Sea beginning in the second half of 2000.

Fatigue Resistant Thread FormA modified thread form that can be applied to either pin or boxconnections has been developed that reduces stress in thethread roots. The reduction in stress intensity providesimproved fatigue endurance. The stress reduction isaccomplished by machining an enlarged radius into the root ofthe thread (Figure 7).

The modified thread form was originally designed andapplied to pin threads primarily on drill pipe tool joints. Whenapplied to pins, a second modification is introduced, where by,the pin thread body is machined on a slightly flatter taper thanthe box. This taper change effectively behaves like a variablepitch thread. It distributes the thread loads more evenly overthe entire thread length and reduces the load at the lastengaged thread by up to 40%. Results from an FEA

evaluation showing the distribution of force along the lengthof the threads for a standard API NC46 connection and anNC46 connection with the modified taper are shown in Figure8.

The modified thread form with the taper change has beenapplied to drill pipe for use in regions throughout the world toenhance the fatigue endurance of the pin tool joints. It hasbeen used extensively in the Middle East, where the presenceof H2S is a significant concern.

Recently, the modified thread form has been applied todrill collar box connections. In this case, the taper change isnot included to simplify dimensional inspection and allow theuse of standard box thread gauges.

An FEA study comparing the modified thread form appliedin the box connection to a standard thread form wasperformed. No stress relief features (API stress relief grooveor API boreback box) were utilized on the pin or boxconnections of the modified thread form model. The modifiedthread form model was compared with the following boxconnection types:

• standard box with no stress relief feature• box with API stress relief groove• box with API boreback featureAll models were based on an API 6-5/8 Regular

connection with an 8 in. OD and a 3 in. ID.Each model included a make-up torque of 50,700 ft-lbs

and was evaluated with bending loads equivalent to a 10deg/100 ft and a 20 deg/100 ft dogleg. The results of the FEAare shown in Table 2.

The modified thread form results in a significantly lowerstress level at the last engaged thread of the box compared tothe standard API thread form. The modified thread form alsocompares favorably to the box with the API stress reliefgroove and the API boreback box. At a 10 deg/100 ft doglegthe stress level with the modified thread form is 17% lowerthan a standard box with no stress relief feature, 11% lowerthan a box with an API stress relief groove and 14% lowerthan a box with an API boreback box. With a 20 deg/100 ftbending load, the stress level with the modified thread form is18% lower than a standard box with no stress relief feature,11% lower than a box with an API stress relief groove and13% lower than a box with an API boreback feature.

A major advantage of using the modified thread form ondrill collar boxes instead of the API box stress relief groove orAPI boreback box feature relates to the amount of material lostfrom re-machining the connection. Both the API box stressrelief groove and the API boreback feature significantly add tothe length of material that must be removed to effectively re-machine a worn or damaged connection. The modified threadform provides a larger reduction in stress level and betterfatigue life than either the API stress relief groove or theboreback feature. In addition, using the modified thread formreduces the length of material that must be removed to re-machine the connection by approximately an inch or more.

The modified thread form has been successfully used ondrill collars to enhance the box fatigue life in well applications

IADC/SPE 62785 NEW DEVELOPMENTS IN DRILL STEM ROTARY SHOULDER CONNECTIONS 5

in Canada. Since drill collars are often scraped when they aretoo short to re-machine the connections, the modified threadform can increase the overall life of the collar.

ConclusionContinued advancements in technology are essential to meetthe challenges our industry faces today and in the future.Three advanced rotary shoulder connection designs have beendeveloped for harsh conditions and improved performance.The second-generation double shoulder tool joint connectionprovides increased torsional capacity, promotes morestreamline geometric configurations and tolerates more tooljoint wear than standard API rotary shoulder connections.

A version of this double-shoulder connection is availablewith a gas tight metal-to-metal radial seal to allow drill stemtesting , high pressure workover operations and enhancedsealing in underbalanced drilling applications.

A modified thread form that improves fatigue life has beendeveloped for use on drill pipe pins and drill collar boxes. Useof this modified thread form on drill collar boxes can permitmore re-machining of the connections and, consequently, alonger service life than possible with traditional API stressrelief features.

The authors hope that these new developments can assistengineers to implement creative solutions to challengingdrilling problems.

AcknowledgementThe authors thank the management of Grant Prideco andUnocal Thailand for their support and encouragement inpublishing this paper.

References1. Jellison, M.J. and Payne M.: “New Drill Pipe Size Improves

ERD and Deepwater Drilling,” World Oil (January 2000)113.

2. API Recommended Practice 7G, Recommended Practice forDrill Stem Design and Operating Limits, sixteenth edition,American Petroleum Institute, Washington, D.C., (August1998).

3. Bailey, E.I., Petrella, J. and Smith, J.E.: “Development ofGas Tight Seal for Tool Joint,” paper SPE 49202 presented atthe 1998 SPE Annual Technical Conference and Exhibition.New Orleans, September 27-30.

SI Metric Conversion Factorsft x 3.048* E – 01 = m

in. x 2.54* E + 00 = cmlb x 4.448 222 E + 00 = N

psi x 6.894 757 E + 00 = kPa

* Conversion factor is exact.

Table 2 – Summary of Connection FEA Results

Stress Intensity at Last Engaged Box Thread Root (psi)

Model Description 10 deg/100 ft 20 deg/ 100 ft

Standard Box 171,734 240,087

API Stress Relief Groove Box 160,528 220,717

API Boreback Box 165,394 226,047

Modified Thread Form 142,441 196,487

ConnectionType

OD(in.)

ID(in.)

Number of Tests

Actual Material Yield Strength

(ksi)

Calculated Torsional Rating Based on Actual Material Yield

Strength (ft-lb)

Calculated Torsional Rating Based on 120 ksi Yield

Strength (ft-lb)

Minimum(ft-lb)

Maximum(ft-lb)

XT57 7 4 1/4 5 N/A N/A 94,340 98,571 119,085

XT54 6 3/4 4 3 132.9 95,915 86,605 90,000 1 127,197

XT39 4 7/8 2 9/16 1 129.4 38,935 36,107 49,523 N/A

XT38 4 3/4 2 9/16 2 129.4 35,852 33,248 33,283 48,632

XT31 4 2 4 137.5 23,987 20,934 28,100 34,100

1 - Torque test machine inadvertantly set to dump at 90,000 ft-lbs (connection did not yield).

Test ResultsTorsional Strength

Table 1 - XT Connection Torsional Strength Test Data

6 M. J. JELLISON, S. P. HASSMANN, D. COTANDA JR., D. SNAPP IADC/SPE 62785

Figure 1 – eXtreme Torque is a second generation double shoulder drill pipe connection. XT provides increasedtorsional capacity, promotes more streamline configurations and tolerates more tool joint wear than standard APIrotary shoulder connections.

Figure 2 – eXtreme Torque and HI TORQUE in the power-tight make-up postion. The secondary torque stopincreases the torsional strength compared to a standard API tool joint connection.

Figure 3 – Comparison of eXtreme Torque and HI TORQUE. The flatter taper of XT increases the secondaryshoulder area resulting in more torsional capacity.

Primary Shoulder

Secondary ShoulderPin base Box Counterbore

Pin

Box

HT

XT

HT

IADC/SPE 62785 NEW DEVELOPMENTS IN DRILL STEM ROTARY SHOULDER CONNECTIONS 7

Figure 6 – Metal-to-metal radial seal provides gas-tight pressure integrity.

010,00020,00030,00040,00050,00060,00070,00080,00090,000

3-1/

2 X

1-3

/4

4 X

2-5

/32

4-3/

4 X

2-9

/16

5-1/

4 X

2-1

3/16

6-1/

4 X

3-1

/4

6-5/

8 X

3-1

/2 7 X

4

8 X

5

Tool Joint Dimensions (in.)

Mak

e-u

p T

orq

ue

(ft-

lbs)

API

HT

XT

Figure 8 - The slightly flatter taper of themodified pin distributes the thread loadsmore evenly over the entire thread lengthand reduces the load at the last engagedthread by up to 40%.

Pin NosePin

Seal

Box

Threads

Figure 7 - The enlarged root radius of themodified thread form reduces the stressconcentration at the thread root.

Enlarged ThreadRoot Radius

API ThreadForm

Figure 4 – Maximum make-up torque or workingtorque comparison for API, HT and XT connectionswith various tool joint sizes.

Figure 5 – XT vs. API Tool Joint DiametricalWear ComparisonNote – Some XT diameters may not be achievalbe due to connectiondimensional constraints (minimum box face thickness requirement)

XT vs. API Tool Joint Diametrical Wear Comparison

0.563

1.297

0.313

0.812

0.469

0.850

0.312

0.770

0.188

0.531

0.000 0.200 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800 2.000

5-1/2 FH

XT55

NC50

XT50

NC46

XT46

NC40

XT40

NC38

XT38

Connection

Allowable Diametrical Wear from New to Premium Class (in.)

3-1/2" 13.30# S-135

5-1/2" 21.90# S-135

5" 19.50# S-135

4-1/2" 16.60# S-135

4" 14.00# S-135

0.735 in. difference(131% increase)

0.500 in. difference(160% increase)

0.344 in. difference(183% increase)

0.458 in. difference(147% increase)

0.381 in. difference(81% increase)