The Drilling Services Surface Coring drill crew used the powerful LF350e along with the new, patented XQ wireline coring rods featuring W-Wall, and the new Longyear diamond bits to successfully directionally drill at an angle of 65 degrees to the client’s required depth – which was almost 10,500 feet (3200 meters). An impressive feat in and of itself, the project had measurable productivity gains and proved the newest Boart Longyear rigs and tooling make a real difference in the field. 

With innovative features of the drill rig, combined with the deepest rated coring rods in the market and the fastest, smoothest cutting bits, the project’s success was also attributed to the talent, experience, and technical expertise of the crew.

Boart Longyear has combined proven technology from its most popular surface coring drill rigs to create the powerful LF350e.The forward tilting head design simplifies the rod handling process and reduces the need for operator intervention and maintenance. The rod breaking clamp is a hydraulic breaking device which means no wrench under power. The foot clamp rotates to break rod joints located between the foot clamp and rod breaking clamp. The rig also features a heated and air conditioned drillers cab to protect the operator from the elements and overhead hazards. Utilizing CAN bus communication and PLC programming, all LF350e functions are controlled electronically. The “e” in LF350e refers to the fully electronic control system. The rig is designed ergonomically to lessen fatigue and stress to the driller and helper. The LF350e has adjustable wireline speed to be able to set to lower the over shot and then pull the tube, which allows a hands-off safer approach. This is just one-way ergonomic design plays a part in reducing fatigue with this drill rig. The beauty of Boart Longyear’s business model of both contract drilling services and a drilling products business is access to immediate, direct, unfiltered feedback from drillers in the field. Drill rigs built for drillers.

A unique combination of -20 degree self-locking reverse flank angle on the threads and symmetrical load distribution when combined with W-Wall double-annealed mid-body, make XQ wireline coring rods some of the deepest rated coring rods in the market. XQ has an increased negative flank angle from of -20 degrees compared to -10 degrees in RQ rods. The increased negative flank angle combined with the double-start threads, nearly eliminate box bulging and provides greater strength in high torque applications.

Patented XQ joints have opposite double-start threads that are self-aligning so mating engages smoothly. This provides a balanced load response and double the contact area, which means half the contact pressure. This symmetrical load distribution increases load capacity significantly for stronger rods with deeper capacity. The lighter drill string increased drill rig depth capacity and reduced fatigue in driller's when manually tripping. The enlarged inner diameter also significantly reduced inner tube tripping time for improved productivity.

The new NXQ and HXQ W-Wall coring rods feature patent-pending, double-upset tubing, with the same overall weight reduction and faster wireline tripping speed as V-Wall. However, the standard wall thickness in the middle of XQ rod eliminates premature mid-body wear and resists bending, performing like straight wall tubing.

As all Boart Longyear coring rod, XQ W-Wall tubing is cold-drawn from high quality, North American alloy steel, uniquely processed to Boart Longyear specifications.

Boart Longyear has successfully created a chemical bond between diamond and matrix, which is stronger than the diamond itself. The increased diamond projection and improved face flushing create a bit with more versatility, higher penetration rates, and longer life. The Longyear Bits are similar to large diamond bits, but with the easy, smooth drilling characteristics drillers prefer. This means increased productivity throughout the entire operation, and ultimately more core.

To support higher penetration rates, the new Longyear formulas are combined with a new, more open, express geometry. Tapered intermediate waterways improve flushing and prevent accumulation of debris. Designed for fast cutting in competent ground, the new express geometry is available in our 16mm crown heights to maintain bit life at higher cutting speeds.

The unique Razorcut protrusions on the face of the bit contain diamonds that enable the bit to begin cutting right out of the box – even in the softest ground. The arrangement of these protrusions also improves the tracking and balance in the hole when drilling begins.

As part of an extensive global test program, employing nearly 10,000 rods at 30 different sites, one of the first strings of NXQ rods were deployed to the Boart Longyear Drilling Services expert underground drilling teams operating in the Sudbury mining camp.

After drilling through the entirety of 2017 and into 2018, the rods have achieved over 20,700 meters of drilling versus a typical life of approximately 12,000 meters on NRQ rods.

Typical rod life depends on several factors, but the greatest affecting rod life is hole depth. Deep holes tend to increase midbody wear due to the lateral loading and drag caused by helical whirling as well as the greater pullback and torsion required to drill with heavier drill strings. The joints on shallow holes, on the other hand, see a lot more wear and tear as the rod string is tripped in and out of the hole more frequently. On balance, shallow hole rod strings may need to be replaced more often than deep hole strings.

The new XQ holds up during “make and break” comparison testing: 168 cycles, right, compared to new, left.

Rod retirement is typically the result of midbody wear, thread wear, or box end wear. 

Joints that are subjected to high torque loads compress the box end shoulder. High drilling torque can be required in deep down holes but also for short inclined holes underground. High torque can also be locked into the joints as the result of a load spike or dynamic load response. The resulting box shoulder compression causes ‘bulging’ that dramatically increases wear and reduces load capacity as the material wears thin. On traditional single start thread joints, this is observed as a small section of noticeably thin shoulder, nearest where the threads mate.

Box end wear can also result from poor rod handling practices. For example, every time mating rods are accidentally misaligned and ‘stabbed’ during make-up, even lightly, then a small leakage path is formed across the box shoulder face. The leakage from stabbed joints will accumulate and can significantly reduce fluid flow to the bit if excessive. Another source of box wear is caused by excessive deviation or a combination of excessive thrust and rotation speed which creates lateral loading and drag that overheats the box shoulder resulting in ‘heat check cracking’. In heat check cracking, a thin skin of outer material is embrittled and cracks axially, growing across and through the box threads.

Rods can also be retired due to thread wear, which occurs during make and break. Drillers can visually check remaining wear life by monitoring the standoff gap between mating rods, when the pin end is initially stabbed into the box end and the first turns of mating threads contact. Normally multiple turns of thread are visible at this point, but the standoff gap can drop by a full turn of thread given excessive wear. Premature thread wear and retirement can be caused by poor make and break settings. During make and break, the threads are only partially mated which significantly increases contact stresses and wear rates given any load. If there is any tension load, during make or break, then this wear occurs on the thread load flanks which directly reduces drilling load and depth capacity. Always adjust make and break settings towards zero load or slight thrust load, (i.e. increase feed or reduce rotation speed to avoid tension load on the load flanks).

The operators reported that make-ups were virtually jam-free and that the performance and the fit of the joints remained consistent throughout, due to the self-aligning double-start threads.

Underground Coring Canada Division Manager, Mike Garton, said about this string and others, “The new XQ thread provides the smoothest making and breaking of any rod I have used in my 25-year career in drilling. The XQ rods align better and don’t require back-turning the rods to start – saving time. Jamming rods during making and breaking lowers productivity, so not having the rods jamming means more meters. The XQ rods coming out of the hole are not showing the typical box or thread wear, which means the rods last longer too. The strength and depth capability are by far the best in the market. When drilling deep holes that need to hit specific targets or underground drilling, this rod outperforms them all. I highly recommend the XQ wireline coring rods.”

Chris was also recently recognized by Mining Magazine in Exploration as part of their Mining Magazine Awards.

On this episode, ahead of the official launch, Chris discusses the benefits of XQ rods and how the new features compare to RQ rods as well as giving a shout out to Design Engineer, Anthony Lachance, and the North Bay manufacturing plant.

The top three benefits of XQ rods are:

1.   Easier and faster make and break with double auto-start threads
2.   Longer thread life – double over RQ rods
3.   Up to 60% stronger than RQ rods

Learn more about XQ Rods

We would love to hear your questions and comments below. Thanks for listening and if you liked this episode, share it on LinkedIn, Facebook, or Twitter. 

Drill rod joints need to maintain their strength by resisting wear against the hole, and the wear of make-ups and break-outs due to bit changes.

With the pending release of Boart Longyear’s third generation XQ drill rod, this article reviews how each generation delivered breakthroughs in load capacity and wear life, substantially boosting reliability and productivity. The original Q drill rod joint is renowned for introducing coarse, tapered threads with a self-locking “interference fit,” but it had room for improvement.

As the thread’s load flank (loaded face of each thread) wore, the joint load capacity dropped, leading to failure: threads jumped, box ends expanded and climbed, or pin ends snapped from fatigue. To address these types of issues, Boart Longyear added hardening to the top half of the pin thread to maximum hardness (60 HRC), creating a significant hardness difference between pin and box. This hardness difference minimized wear compared to the rapid adhesive wear on threads of similar hardness.

Wear debris clings to a failed non-case-hardened joint after 12 cycles. 

Case hardening is unmatched in protecting the thread from wear, while keeping the toughness required to carry drilling loads. Competing drill rods are typically through-wall hardened to 32 HRC. Without case hardening (no “difference in hardness”), wear life is limited and load capacity degrades with each make and break.

In simple repeated “make and break” comparison testing, competing non-case-hardened rods were recently shown to fail at between 12 and 73 cycles, whereas Q and RQ joints withstood more than 150 and 300 cycles, respectively. The Q thread profile also had room for improvement. The positive-angled load flank (+15 degrees) tries to open or expand the box end under tension, which limits depth capacity and accelerates wear against the hole.

XQ threads. 

 A short-lived design variation, the MQ, variations of which are still offered by some competitors today, reduced the load flank angle (+2 degrees) to address this issue. However, the MQ was soon superseded by the second-generation RQ drill rod in 1999. The patented RQ joint improved load capacity and reduced joint expansion with a reverse-angled load flank (-10 degrees), which tries to shrink or close the box end, mimicking the natural load response of a continuous tube.

Wear life was doubled by reducing the number of turns during make and break. Many in the industry have applauded the RQ as being the most reliable rod for demanding, deep or deviated holes, both surface and underground. The next breakthrough meant overcoming two limits inherent to all threaded joints.

First, all threaded joints inherently suffer uneven load distribution, favoring the first point of mating contact because the male portion is under tension and the female portion is under compression. The stress and strain at this first point of contact produces uneven joint expansion and wear, commonly exhibited as leakage or a thin portion of the outer shoulder.

Patented XQ joints feature opposite double start threads that provide a balanced load response and double the contact area, which means half the contact pressure. This advancement doubles the make-and-break test cycles over the RQ. Additionally, XQ significantly increases load capacity by utilizing a load flank angle of -20 degrees, double that of the RQ, allowing for depth ratings beyond 4,000 meters, or 30 percent more than the RQ.

Second, the start of each thread typically requires gradual partial thread transitions that lead to rapid wear and wedging, followed by jamming and cross-threading, which would be problematic for simple double-start threads.

The new XQ holds up during “make and break” comparison testing: 168 cycles, right, compared to new, left.

XQ features an innovative self-aligning thread start geometry, ensuring mating threads engage smoothly, without wedging or jamming. Smooth starting, in combination with case hardening, significantly improves both productivity and wear life.

Finally, consider Boart Longyear’s V-Wall tubing option that made drill strings up to 30 percent lighter, thanks to a thinner wall mid-body. Operators welcomed this feature, as heavier rods can reduce productivity, especially in deep or deviated hole applications.

XQ joint. 

A lighter drill string reduces driller fatigue from manual handling and increases drill rig depth capacity, and the enlarged mid-body significantly reduces inner tube tripping time, all of which improve safety and productivity.

However, the thinner midsection is prone to uneven wear distribution concentrated at the mid-point. The new NXQ and HXQ drill rods exclusively feature patent-pending double- upset W-Wall tubing, with overall weight reduction and tube tripping capability equivalent to V-Wall.

A midplaced section of standard thickness improves mid-body wear life and stiffness, approximating standard wall tubing. Similar to the RQ, W-Wall tubing is cold-drawn from high quality, North American alloy steel, uniquely processed to Boart Longyear specifications.

As global field trials progress, so does our confidence and excitement about the advantages the new XQ rod will bring. Its strength, wear life and easier make and break will reduce downtime, lower operating costs, increase productivity and expand drilling capabilities, as well as maintain the operator’s reputation with clients.

The image on the right shows the result of insufficient make-up torque. A minimum torque should always be applied no matter how shallow the hole.

The make-up torque should also increase with depth of hole. This way, the joint stays tight as rod tension increases or passes through deviations, limiting fatigue failures without overloading the pin end.

Whether through chucking, hammering joints loose or handling, rods accumulate dings and dents that act the same as flaws, starting cracks and producing rod failures.

Result of insufficient make-up torque.

In the image below, the rods have indents all over the surface from rod handler rollers.

Indents from rod handler rollers.

As a result, the rods cracked axially, perpendicular to the load. Upon investigation, the rod handler hydraulic rollers were set to their maximum value, well above what is required to hold even the largest rod safely.

Reducing roller pressure reduced the tooth indent size and eliminated the source of fatigue cracking. As a rule, rods with defects on 10 percent of the wall or larger (0.019 inch for NQ rod) can experience premature failure due to fatigue cracking. When discovered, these rods should be removed from service and the cause of the damage identified and eliminated.

It is common to see bright polished areas on rods, associated with rubbing on the casing or formation, which can cause cracking. When a section of rod is rubbing, it rapidly heats and cools, causing cracks known as heat check cracking.

This rod failure can be prevented by ensuring that rods are well lubricated either by drilling fluid or, in the case of lost circulation, rod grease. If polished areas are observed on box ends, check for the beginnings of these cracks and pull the rods out of service before they cause a string failure.

The picture on the right shows adhesion galling wear after 30 make-and-break cycles for rods with the same hardness for pin and box (not Boart Longyear).

Threads displaying this level of wear should be measured to make certain sufficient thread engagement still exists and, if in doubt, retire the rod. Use of worn threads will rapidly wear even new rods, increasing rod usage and chances of rod failure.

Boart Longyear case hardens its rod pin threads, creating a differential hardness to extend thread life by more than two times, depending on application.

Adhesion galling wear.

Any of these failures will add cost per meter. Rather than focusing on price, measuring cost per meter of rods will determine the true cost to a contractor’s operation and lead to the purchase of the highest-quality rods available.

However, Boart Longyear has recently made improvements to the system, significantly increasing reliability and performance.

Primarily, wireline systems require a sample-receiving inner tube completely independent to the rod string, while located at the bottom of the rod string, in the outer tube behind the drill bit.

Mounted at the top of the inner tube assembly is the head assembly, which includes the critical latch mechanism required to hold the inner tube while receiving the core sample and to release the filled inner tube for wireline retrieval.

A device called the overshot is attached to a wireline cable and lowered or pumped into the hole until it captures the head assembly, allowing the inner tube to be pulled or hoisted back to the drill rig by use of a winch or hoist.

Full Hole Locking Coupling

Stabilized Locking Coupling

The Latch Seat

In order to receive the latches deployed from the head assembly, couplings are inserted into the drill string to provide an enlarged interior opening or seat. In the original system, the latch seat was formed by mating two couplings. The first coupling, mated to the drill rods above the inner tube, is known as the locking coupling. The lower coupling, known as the adapter coupling, mates between the locking coupling and the outer tube, below which the inner tube is housed, and in turn to the reaming shell and drill bit. The end face of the male end of the locking coupling serves as the load bearing face for the latch mechanism.

Unfortunately, all pivoting latch mechanisms require a significant amount of “play” or axial clearance in the latch seat to allow for the pivoting latch movement, which results in inner tube play and poor system performance in difficult ground. In fact, an inner tube with a wedged core, or an overfilled inner tube, can be sufficiently loaded up against the latch seat such that the latches are unable to pivot in retraction. This often results in a stuck tube, potentially requiring the costly retraction of the drill string.

 In more recent Roller Latch systems, an improved integrated locking coupling eliminates the secondary joint and incorporates a mid-placed interior groove which serves as the latch seat. Additionally, roller latches drop away, eliminating the need for axial play and improving system performance in difficult ground.

Primarily, the latch seat must resist the reaction of the full thrust load from the drill whenever the driller is pushing through difficult, “blocky” ground. That is to say, when the core sample temporarily sticks or wedges in the inner tube (or when the tube is full), the thrust in the drill string (weight on bit) is fully resisted by the inner tube, the latch mechanism, and the locking coupling. However, the seat has a depth of about a third of the drill string thickness, which limits potential load-carrying capacity.

Latch Mechanisms and Locking Coupling Material

The head assembly of the original Q system incorporated a latch mechanism consisting of a pair of pivoting latches, deployed by a wire “butterfly” spring and retracted by the impact with the bottom of a slot in the latch retracting case when retracted by the wireline overshot.

Now obsolete, these latches had only 8mm (5/16”) thickness, which produced a very small mating contact area on the latch seat. This resulted in contact pressure and material stresses which often exceeded the strength of the latch seat when drilling difficult ground conditions. In some cases, the latch seat material would yield and allow the latches to push into the locking coupling, resulting in a stuck tube. At a minimum, the high wear rate of the latch seat was a maintenance issue.

In 1998, Boart Longyear once again secured its position as the leading innovator in wireline technology by introducing the patented Link Latch mechanism. This innovation virtually eliminated “stuck tubes” by providing mechanical leverage during wireline retraction, directly pivoting the latches into the retracted position, whereas conventional technology attempted to indirectly push the latches while fighting poor mechanical leverage and interference with the latch seat.

Additionally, the latch thickness was doubled to 16mm (5/8”), which cut the latch seat contact pressure and stresses in half, improving wear life and reliability. However, inner tube play is required for the pivoting latches.

In 2012, the launch of Roller Latch technology included a significant upgrade to all Boart Longyear locking couplings. Heat-treated, alloy steel material provided substantial increases in strength (40% increase) and hardness (wear resistance). This provided much greater thrust capacity and reliability in pushing through difficult drilling conditions, but also significant improvements for other locking coupling features as discussed below.

Locking Coupling Wear Pads

Situated at the top of the outer tube, the locking coupling can also act to stabilize the outer tube and reduce hole deviation. This is achieved through the addition of wear pads which act as a bearing surface against the drilled hole.

Boart Longyear offers two styles of locking couplings, “full-hole” and “stabilized.” While both are cut from the same high-quality alloy steel tubing material used for wireline drill rods, full-hole locking couplings have an over-sized outer diameter with four equispaced flats that are cold-drawn along each length.

While the annular area between the flats and the drilled hole provide passage for drilling fluid and cuttings, the over-sized rounded portions are induction case-hardened to provide hard, long-lasting, abrasion-resistant wear pads over the body length.

Full-hole locking couplings perform well in competent ground conditions where the hole is uniform and cuttings are fine. Conversely, poor ground conditions can significantly limit drilling performance and cuttings circulation, or generate excessive drill string torque or feed requirements.

Laser clad wear pad detail

Laser clad wear pad detail

Magnified section showing tungsten carbide in matrix

Locking Coupling Wear Pads

Situated at the top of the outer tube, the locking coupling can also act to stabilize the outer tube and reduce hole deviation. This is achieved through the addition of wear pads which act as a bearing surface against the drilled hole.

Boart Longyear offers two styles of locking couplings, “full-hole” and “stabilized.” While both are cut from the same high-quality alloy steel tubing material used for wireline drill rods, full-hole locking couplings have an over-sized outer diameter with four equispaced flats that are cold-drawn along each length.

While the annular area between the flats and the drilled hole provide passage for drilling fluid and cuttings, the over-sized rounded portions are induction case-hardened to provide hard, long-lasting, abrasion-resistant wear pads over the body length.

Full-hole locking couplings perform well in competent ground conditions where the hole is uniform and cuttings are fine. Conversely, poor ground conditions can significantly limit drilling performance and cuttings circulation, or generate excessive drill string torque or feed requirements.

Quick pump-in roller latch stabilized locking coupling section showing latch groove and brake groove

Laser clad wear pad detail

Stabilized locking couplings (formerly known as “conventional” style) utilize sets of wear pads consisting of tungsten carbide-bearing materials. Tungsten carbide offers wear resistance that is orders of magnitude greater than that of hardened steel, providing a reliable, longer-lasting bearing surface than the full-hole style.

Also, greater spacing between the wear pads, and in the annular area between the coupling body and the hole, ensures efficient passage of drilling fluids and cuttings in all ground conditions.

Originally, stabilized coupling wear pads were applied through a laborious manual process where welding technology was used to melt welding rods, consisting of tungsten carbide in a metal matrix known as “hard facing,” and bond the rod material to the coupling body.

A large amount needed to be added to be able to grind back down to a reasonably sized flat wear pad, and the resulting shape was difficult to control, which degraded the capacity to pass fluid and cuttings. 

In addition, an excessive amount of heat was required, which softened the steel body and weakened the coupling. On some couplings, hard facing was also applied to the latch seat face for wear resistance, but due to the manual welding process, this could soften the underlying latch seat to the point where latches could protrude through the seat under normal loads.

Again, the launch of Roller Latch technology included another significant upgrade to all Boart Longyear stabilized locking couplings. Laser cladding technology enables the precise application of wear pads containing a significantly greater density of tungsten carbide and with very little heat.

Stabilized wear pads are provided in an efficient spiral shape, which promotes passage of drilling fluid and cuttings. Comparative laboratory wear testing has shown an improvement of over 10 times (testing to ASTM G65), which typically translates to more than double the wear life in the field.

Locking Coupling and Head Assembly Interaction

While Boart Longyear has improved the wear resistance of latches and latch seats, abrasive wear is caused by their interaction during normal drilling operations.

Significant relative rotational motion can occur between the Link Latch head assembly and the drill string when there is insufficient loading or mating contact friction. This can result in rapid wear between the latch seat and latches, as well as between the head assembly landing shoulder and the outer tube landing ring.

Locking couplings for the Link Latch head assembly are optionally available with a small drive key or “tang” which is an integral, partial extension of the male end shoulder which protrudes beside deployed latches. As such, rotation of the drill string will drive rotation of the head assembly in unison.

Conversely, the patented Roller Latch mechanism is self-locking in rotation. As the rollers are centrifugally deployed, if there is any relative rotational movement with the drill string, the rollers are wedged between the locking coupling and retracting case to ensure the head assembly is always driven with the drill string.

This self-locking action provides a significant increase in the wear life and reliability of the landing ring, landing shoulder, latch rollers, and the locking coupling latch seat.

Drill Rod String Connection

Locking couplings include both a male outer tube thread and a female wireline drill rod thread connection, in order to mate directly to the drill rod string.

The outer tube is significantly thicker and stiffer than the drill rods, and is stabilized by the drill bit, reaming shell, and locking coupling wear pads. Conversely, the drill rod string is supported only by the formation, and is subject to significant dynamic loading as a result of drilling loads, vibration, and system harmonics.

As such, the locking coupling connection is critical to performance in demanding drilling conditions, wherein the recently improved heat-treated material provides strength and wear resistance.

Boart Longyear’s proprietary Q and RQ wireline drill rod joints utilize tapered threads for easy make and break, and feature engineered thread forms, a precise interference fit, and a unique combination of heat treatments to maximize load strength and wear resistance.

Boart Longyear facilities produce these precision thread connections to exacting global standards, controlled to a proprietary master gauging system.

As is well understood across the wireline drilling industry, in order to avoid joint failures, never inter-mix genuine Boart Longyear drill rods, couplings, or adapters with products produced by unlicensed third parties.

Ready to look into Boart Longyear's rods?

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