Tool Joints V1

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Sugar Land Learning Center - SLCSchlumberger

Anadrill

Tool Joints

Design

Torquing

Inspection


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Objectives

At the end of this presentation you will be able to

l List the five criteria that are the requirement for a

good tool joint design.

l List the five criteria that go into the design of a

tool joint.

l List 5 common joint types and drillpipe grades.

l Describe hole a drill joint makes its seal.

l Describe why Bending Strength is important.

l Describe the consequences of incorporate torque

in a connection.

l State where the most stress in a connection is.


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Objectives

l Identify a stress relieved connection.

l List 5 reasons why tool joints are inspected.

l Describe (briefly) 5 methods of inspection.

l Describe 4 joint failure modes.

l List the major steps in torquing a connection.

l Demonstrate how to find the correct joint torque

from the torque charts in the PowerPulse UOP.


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The primary requirement of a tool joint is to allow the connection of a number ofpieces of pipe together to make a continuous string of pipes. However there are severalother critical requirements of the joint used in the drilling environment.

It must satisfactorily connect two pipes together and not unscrew under the action ofnormal drilling operations.

It must provide a hydraulic seal such that drilling fluid may be pumped down theinside, of the string of pipe, under high pressure (several thousand PSI) withoutleakage.

It must be able to withstand normal drilling torque and bending from reasonablerotation and doglegs without parting or unscrewing.

It must be able to resist most reasonable conditions being made up and broken out, thatexist in the drilling environment, like dirt particles in the threads.

Finally it must have a reasonable service life. Although this will heavily depend onmaterial type as well as design.


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Why Have a Connection?

To make a continuous length of pipe

Provide hydraulic seal

Transfer torque from surface to bit

Pin Box


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The connection or tool joint is a tapered threaded jack screw that forces the shoulderstogether in such a way as to provide a seal at the shoulder face and act a a structuralmember to make the pin equally as strong , in bending, as the the box when made tothe recommended torque. The threads do not form a seal in fact they allow for a openchannel from the bore to the shoulder seal. This space can allow for excess thread

compound, foreign matter and thread wear. It will also allow the Pin to be stabbed intothe Box and make up even if there is drilling fluid right to the top of the box.


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Connection Design Considerations

l Thread Types (profile)

l Material (Grade)

l Sealing

l Bending Strength

l Joint Torque


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There are a number of different types of thread, they differ in their taper, thread profileand teeth per inch. The most common are the thread types such as 7 5/8 Reg forBHAs and 4 1/2 IF for 5 drill pipe. Anadrill does not use regular threads for its toolsinternal connections because the ID of the collars is too great due to the electronicpackages that fit inside them.

Anadrill uses a number of different non-magnetic materials for its tools, these includeaustenitic stainless steel (monel), inconel (a high grade stainless steel) and berylliumcopper (BeCu). Each has various mechanical properties.

Drillpipe is classified by strength as a grade. E grade is very common and so is S gradefor long reach highly deviated wells.

Grade Symbol Minimum Yield

D55 D 55,000

E 75 E 75,000

X 95 X 95,000

G105 G 105,000S 135 S 135,000

V 150 V 150,000

Used U -


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Thread Types & Material

Reg - Regular

NC - Numbered Connections

IF - Internal Flush

H-90 - Hughes

FH - Full Hole


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To identify an unknown tool joint use a Drilco tool joint identifier ruler.

Screwing on a known thread protector is not adequate as many protectors are designedto fit several threads and many threads will screw just together but be unable towithstand any load.


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Identifying a Thread Type

Use a Tool Joint ruler


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The seal keeps the fluid inside the drill pipe which is under very high pressure fromleaking out at the connection. The shoulder face of the box and the shoulder of the pinprovide this seal. The thread does not provide any sealing in fact it allows a channel allthe way round the thread into the center of the collar, this allows dirt or fluid to escapeas the connection is screwed together.

Since the seal comes from the two faces, they must be in good condition with no radialscoring or raised defects, some circumferencial scoring is okay. Any defect in the facesthat may allow fluid to flow from the inside to the outside could lead to a twist off.This is called galling.


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Sealing

The threads DO NOT provide the hydraulic seal

Sealing Face

Box

Pin

Shoulder is the

only sealChannel


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During the life of a collar it will be subjected to continual flexing that will result infatigue failures. Unlike drillpipe, the body of the drill collar is much stiffer than thejoint. This will result in the most flexing occurring at the joint. Consequently, mostdrill collar failures occur in the joint.

As the the collar rotates in a deviated well it will be subjected to cyclic stress which, if

high enough, will cause any small defects in the joint to grow resulting in a crack thatwill eventually cause a twist off. Notches or surface defects around the tool joint willlocalize the stress and increase crack initiation and propagation.

So it is important to try to match the flexing of the pin and box so that the bend at thesame rate but when combined in a properly torque connection they are not so weakthat all of the collar flex is located at the tool joint like a hinge.

The Bending Strength Ratio of a joint combination is an indication of the connectionscompatibility to resist bending. Proper torque is critical for this.


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Bending Strength

Tension

Compression

Joint Flexing


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Like any nut and bolt there is a correct torque for a connection. The connectionrequires the correct torque so that it does not come loose in use, and provides theproper bending strength.

When a pin and box are screwed together as more and more torque is applied themetal of the pin and box will elongate or compress by some amount. This strain in the

metal when the torque is released will clamp the two parts together, friction will stopthe joint coming apart. However if too much torque is applied the pin will stretch toomuch and the box compress too much to the point where the metal will be permanentlydeformed and there will be no strain in the joint allowing the connection to becomeloose. Also if too little strain is applied to the joint then there will be too little frictionforce stopping the connection from unscrewing. Hence the connection will back offunder use. Also, too little torque could result in failure of the connection due tobending stresses.

The correct amount of strain will be a function of the load area, the linear force and ofcourse the mechanical properties of the material of the tool joint. The linear force willbe a function of the thread pitch, the coefficient of friction between the two materials

and the applied torque.Hence working backward from the joint cross-sectional area, the material yieldstrength, the thread design and the friction coefficient; the correct torque to apply canbe calculated.

See section 2.5 of the PowerPulse UOP for the torque specification for any ofAnadrills connection.


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Joint Torque


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In drill-collar joints there are two areas where stress concentration can occur:

Consider a properly made-up joint where the shoulder supports the pin in bending .Maximum flexing occurs in the box threads just beyond the last engaged thread at theend of the pin. Failures begin from the thread root on the inside of the box because thethread acts as a notch. Furthermore, these threads are exposed to corrosive drilling

fluid. Resulting corrosion pits in the thread roots making them points of stressconcentration.

When joints are not properly made up, the shoulders can separate so that the pin is notsupported by the shoulder. It is, however, restrained by the box threads. Thus,maximum bending stress occurs in the thread roots of the first engaged thread near thebase of the pin. Fatigue cracks develop in these thread roots.

Maximum flexing occurs in the box threads just beyond the last engaged thread at theend of the pin. Cracks begin from the thread root on the inside of the box because thethread acts as a notch. Additionally these threads are exposed to corrosive drillingmud, resulting in corrosion pitting in the thread root.

Also as the pin flexes, the shoulder supports the bending localizing tension in the lastthread of the pin. This is made worse if the joint is under torqued.


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Joint Stress

Cracking in last thread of Pin

Cracking in last thread of Box

Stress in

Box

Stress in

Pin


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Stress-relief grooves can be cut in a joint, located near the base of the pin and in thebottom of the box just beyond the last engaged thread of the pin. These relief groovesare intended to release stress concentration in the critical bending areas of the pin andbox. They do this by removing unnecessary threads, which are notches, and replacingthem with smooth, large radius contours. This provides a more flexible joint, less

likely to crack in fatigue, because bending in the joint occurs in areas of smooth reliefsurfaces.

It is essential that the surfaces of the stress-relief areas be free of tool marks, stencilmarks or other notches.

Another modification of the box threads is the Drilco bore back. This design consistsof a straight cylindrical bore in the bottom of the box. Bore diameter is of a size toinsure that the last thread root in the box is covered by the threads at the end of the pin.The smooth bore continues beyond the end of the pin and then is gradually contouredwith large radii to the bore of the collar. A machinist can produce a smooth surface inthe stress-relief area with this bore-back design more easily than he can with theundercut design of the API stress-relief groove.

However, stress relief grooving increases the amount of material which must beremoved when a thread is required to be re-cut, hence shortening the service life of acollar.


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Stress Relief

Normal Pin Pin with Stress Relief Groove

Normal Box Box with Bore BackBox with Stress

Relief Groove


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Joint Inspection


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If we are to run our tools in a drilling environment we must be certain that our drillingtools i.e. collars and connections can withstand the stress and strain they will besubjected to. Any undetected cracks or surface damage that may lead to a crack canultimately lead to a twist off and lost in hole expense to us and our client; or serioustool damage when fluid leaks into our electronics or more severely when flow is

established and washing occurs causing failures and the junking of parts.As the connections are made up and broken out they wear, so it is necessary to assesswhether they still pass the minimum dimensional specifications for that connectiontype. Also, surface damage can occur, particularly in non-mag connections, calledgalling. This causes extra friction in a joint and therefore could lead to under-torquingor if in the surface of a shoulder this could lead to a washout.

Whenever a tool is inspected and passes, a certificate of inspection is issued for thatjoint. This is vital whenever a incident occurs to any Anadrill connection at thewellsite which costs the client money. This is why Anadrill itself does not inspect itsown connections but rather a independent third party. Our client often requires acopy of these certificates before they will run any of our equipment in the hole and in

some cases they will come and inspect our equipment in our base before we ship it tothe wellsite.


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Why Inspect Connections?

l Guarantee the integrity of our connections

l Avoid lost in hole

l Avoid tool damage such as flooding & washouts

l To assess threads for repair

l Customer requirements


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In Ultrasonic a sound wave is directed into the area under inspection and the returnwave is monitored. Any discontinuities or density changes cause changes in thepropagation of the wave. This may indicate sub-surface damage or cracking.

In Magnetic Particle a powder is put onto the test piece and then a strong magneticsource is applied to the piece. The magnetic field strength is highest in areas of sharp

geometry i.e. cracks, therefore the particles will migrate to these areas. The magnetismis removed and the particles washed off, however those inside a crack will not bewashed off and will show up under ultraviolet light, depending on the type of testmaterial used.

Liquid penetrant is very similar in principle to magnetic particle in that the test liquidis drawn into a crack by capillary action and is not removed when the excess liquid iswashed off, so can be seen under UV.

Radiographic method uses X-rays to take a photograph of the area under inspection.Clearly this method is dangerous.

Visual inspection is always carried out as part of any third party inspection where

ODs and IDs are measured and the general appearance of the joint is assessed fordamage. Visual inspection should be carried out by the engineer at the wellsite prior tomaking any connection involving Anadrills equipment. Any suspicious connectionshould not be used and returned immediately to town for professional inspection.


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Inspection Methods

l Ultrasonic

l Magnetic Particle

l Liquid (Dye) Penetrant

l Radiographic

l Visual


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The threads and shoulders of a connection can be damaged through miss handling ofthe collars. This is most likely to occur if the tool has no thread protectors. Even if thetool is sitting on the pipe rack and is not being moved it is vulnerable to damage fromcollision with other items in transit around the rig site. All connections at all timesmust be protected, by thread protectors or baskets. However, as soon as they are

removed from the basket they must have protectors. Whenever lifting Anadrillsequipment, insist on a tag line however short the move. If the load gets out of control itwill be damaged when it hits something.

Over torquing will plastically deform the box and pin reducing the stress in theconnection leading to backoff down hole. Under torquing will allow the joint to overflex leading to cracking and twist off if it has not backed off first.

All Anadrill tools have a dogleg limit for rotation and sliding, exceeding this willcause damage, washouts or twist offs.

Non Magnetic material is prone to failure due to a reaction with certain substances andhigh load; this is called stress corrosion cracking. It is particularly a problem in wellswith Hydrogen Sulfide (H2S).


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Failure Modes

l Mis-handling

l Incorrect torque

l Fatigue

l Stress corrosion cracking


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Making a Connection at the Rigsite


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When picking up the tool always have thread protectors on the tool and have tag lineson the end of the collar if it is not dragged in. Make sure that as the collar comesthrough the vee-door it does not swing freely and its entry to the rig floor is controlledby a rope.

When putting in the slips make sure that the dyes do not rest on any wiring channel or

antenna or anything that looks unable to withstand the compression of the slips. Then,if it is a slick collar, install the dog clamp before unlatching the elevators (all drillerswill do it this way).

Pipe dope is a good-quality viscous lubricant containing powdered metallic lead,copper or zinc and should be carefully applied to the threads and the shoulders. Everysur face must be lubri catedin order to avoid galling on make-up. Do not rely on make-up to spread a glob of lubricant applied to the pin or box. In the workshop a layer ofMoly-duo-lube (an anti galling dry lubricant) is sprayed onto the threads then Kopr-Kote dope is applied before any connection is made up. Kopr-Kote is preferred fornon-magnetic material as non-mag is prone to galling.

Some drillers make a practice of lubricating a new thread, making it up hand tight with

the chain tongs, breaking it out, and re-lubricating it. Then it is made up again with thechain tongs before the rig tongs and high make-up forces are finally applied. Thisprocedure works the lubricant into the surfaces and avoids galling of threads andshoulders on the initial make-up. All drillers should do this.


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Applying Dope


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Before stabbing the connections remove any extender protector caps.

Particularly with the Anadrill connections involving real-time extenders it isimperative to stab the collars together by hand as centrally as possible. Then start theconnection by hand with a chain tong. Remember that if there is a motor with a bendbelow the rotary table, with a bit, turning the rotary table to make connections may

damage the bit, the BOPs, or the riser so should be avoided.


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Stabbing


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As with the slips when placing the tongs on our equipment avoid any wiring channel,hole in the collar or anything that would in your judgment be damaged by placing thetongs on them. Also the tongs on the box connection should be a minimum 6 from theshoulder to avoid compressing the box as the torque is applied, therefore potentiallyunder-torquing the joint.


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Tong Placement


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When you are satisfied with tong placement stand back! And even better stand behindsomething substantial such as a girder or beam, since when a tong breaks or aline/chain snaps it is like an explosion and the parts will seriously damage you.


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Ready to Torque


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The torque is applied by pulling on the end of the tong arm; therefore you must knowthe length of the tong from its center to where the force is applied. Assuming the lineis at right angles to the tong arm then the torque applied will be the product of the armlength and the tension in the cable or chain - line pull.

The Driller will ask you the torque you wish to apply to your connection, this can be

obtained from section 2.5 of the PowerPulse UOP, the tables in this section can beused to calculate the required torque for all of Anadrills tool connections for toolsgreater than 6 OD. The lower of the torque for the pin or box should be used.Anadrills torque are always lower than rig connections because non-magneticmaterial is softer than steel and our IDs are usually much greater than standardtherefore there is less cross-sectional area with which to spread the load over.

Once the torque has been agreed on, the Driller will pull on the tong and measure thetension in the line with a load cell, this will appear on a gauge in the dog house whichyou must be watching as the Driller applies the pull.

Some more modern rigs have an Iron Roughneck which is a hydraulic device whichmakes up the connections, these devices will display torque directly.


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Line Pull

Load CellLine Pull Gauge

Documents

Tool Joints V1