October 2023
Special focus: Advances in drilling

Where do you want to invest your money?

The rugged Delta connection provides wider field inspection tolerances. This case history illustrates how focusing on KPIs can lead to inefficiencies and increased costs, and more importantly, how to avoid this trap.
Guillaume Plessis / NOV Kim Cunningham / NOV

The drillstring is a major asset for a rig owner, and its maintenance is the object of much attention. Drilling contractors face the challenge of justifying the selection of a relevant premium connection technology that will increase the value and efficiency of their rigs on the market. This article will not delve into technology selection but instead focus on maintenance, which can make up the majority of expenditures. 

Over the last few decades, the need for higher performance in torque and hydraulics to deliver more challenging wells and/or improve drilling economics has directed drill pipe connection development. As a result, this brought four main generations of drill pipe connections to the field between the early 1980s and now, which are classified in torque segments as described below: 

  • After optimization, the high-torque segment delivers around 30% more torque than a comparably sized API connection. These connections use API thread forms as a base and are, by nature, simple to run and cost-effective. 
  • The extreme torque segment offers connections that provide about 70% more torque and which started with the launch of the XT™ connection in the late 1990s. These connections typically use proprietary thread forms to deliver higher torque and improve hydraulics. These streamlined connections, cut on thinner walled tool joints, offer a larger bore for fluid pumping and contribute to further improvement of the string’s hydraulics. 
  • In a more streamlined design, ultra-high torque delivers around 85% more torque than an API connection. These connections combine higher-strength material and advanced thread forms to prevent early fatigue failures. 

Around 2014, our industry shifted focus. We realized that exceptional performances are not always necessary for drill pipe connections, especially when they come with higher maintenance costs. Just like not everyone needs a super or hypercar, NOV’s fourth-generation connection, the Grant Prideco™ Delta™, was designed to perform at the top of the extreme torque segment, with ease of use and low cost of ownership. NOV reduced costs by creating a more rugged design that can perform with higher tolerance for damage. Delta has relaxed inspection criteria and can receive more minor repairs (reface) before it needs to be extensively rebuilt (recut). 

Fig. 1. Types of connection repair and associated material loss.

Fig. 1 shows material losses for various types of connection repair. A reface consumes 1/32 in. of tong material and touches only the two shoulders of the connection. A chase and face will require cutting around 1 in. of material and creating new threads where the previous ones were. Lastly, a full recut will take a few inches of material to cut new threads under the roots of the previous ones. The higher the tong loss, the more product life is consumed, as the length available for repairs is limited. On average, Delta connections can be repaired four times throughout the life of the drill pipe.  

NOV has monitored inspection reports for a few years to ensure the new connection benefits its owner. With the help of key customers, we gathered data from three inspection companies and compared them to other connection designs. The focus was on the recut numbers, as a connection design can impact them. On the other hand, refacing numbers are of less interest, as the connection design does not influence them because they are operationally induced—by corrosion, enhanced by fluids, or by mishandling. The findings showed that the recut rate for Delta connections stabilized around an average 6% of the inspected, about half the number seen for other connection designs, based on a large sample base.  

Fig. 2. A technician buffing a connection.

We were confident that this would be the norm until owners reported higher numbers. An investigation revealed that: 

  • The market for inspections between rig moves is competitive. They must be fast and affordable. The main justification for speed is the need to have enough pipe for the rig to run the drilling operation. 
  • Part of the inspection process is the connection cleanup, which takes time and conflicts with the above-required need for speed. Cleanup should be more than just removing thread compound and fluid residues. If necessary, buff the connection, which removes raised metal around the crests of the threads, as shown in Fig. 2. 
  • In addition, part of the inspection process is visual and somewhat subjective. It is known that two inspectors looking at the same connection can reach a different conclusion. The less time you give an inspector, the more likely he/she will lean toward rejecting rather than accepting the connection. 

After inspection, the pipe that needs repair is sent to a licensed workshop to recut the connections. Reface can either take place on location or at that workshop.  

Owners who saw high connection rejection rates started organizing secondary inspections to confirm these numbers. Through this process, they performed the buffing and potential hand repairs allowed, per the original equipment manufacturer’s (OEM) field inspection procedure. As a result, the owners got a very different picture, finding that many originally rejected connections were actually fit for service with minimal care. 


NOV became involved in a case that exemplifies the situation mentioned above. This case started when a pipe owner reported an abnormally high repair rate of 71% after a third-party supervised inspection. The inspection revealed that out of 712 drill pipe joints (1,424 connections), 1,016 connections required repairs, with 55% needing recut and 16% needing to be refaced.  

Fig. 3. Inspection case history, showing the impact of using the OEM’s inspection criteria.

When the repair workshop received the pipe, a second inspection started, adhering strictly to the OEM’s requirements, which we believe the industry has not yet adopted or assimilated. Once again, a different picture emerged. Fig. 3 shows the split after the initial inspection on the left, with the accepted in green, the connections needing refacing in orange, and those marked for recutting in red. One can see how the original red sector was redistributed in the middle. Finally, the outcome on the right reflects the use of the OEM’s inspection criteria. 

After this second inspection, only 100 out of the 521 reinspected joints of pipe required repair in the shop, with a large majority of connections needing reface and only 12 recut. Even though transporting these many pipe joints from the rig site to the repair workshop was unnecessary, it was still worth giving the string a second look. This significantly reduced the number of connections needing a recut, which will, as a result, not lose one-quarter of their lifespan. 

This Delta connection story serves as a foundation to reflect on the more essential investment question and how subsequent choices can defeat people’s best intentions. 

Where do you want to invest your money, then? The drilling contractor has chosen to use an advanced connection technology to provide better performance to its clients while enjoying reduced maintenance costs. Due to the typically lower repair rate after inspections, they do not need to buy as much pipe, since less pipe is expected to require repair. The contractor initially intended to keep as much pipe available on the rig site after a fast-paced inspection service. However, the decision backfires when this need for speed creates the opposite effect. As the proper inspection criteria were not used, more products were rejected and sent offsite for repair. Then, less pipe is available on the rig site, and the driller will likely need to rent some pipe to keep drilling. 

The situation gets worse, as this leads to repair workshops being saturated with work that is not supposed to come their way in the first place. As a result, their standard lead times to repair products increase. In the above example, repairing these 1,000-plus connections would have taken weeks, when the only 312 found in the end could be processed within days. Obviously, this would have inflated the repair bill drastically and created a negative perception of the technology. 

An additional cost that may not be immediately apparent is the loss of product life. This cost is often overlooked when evaluating technologies. Overzealous inspection can lead to some products reaching their end-of-life sooner, resulting in higher attrition rates. If one repeats this bad practice four times a year, a significant portion of that string will be gone within one year, and more pipe will need to be purchased. Needless to say, this will be a painful CAPEX decision. 

This is where a sole focus on key performance indicators (KPI) can fail you. An efficiency quest can increase the number of repairs and bring additional costs: trucking, repair, and asset life reduction. If too little pipe is available at the rig site, more will need to be brought in or rented. The volume of pipe reaching the repair workshops can become problematic, causing lead times to stretch, further increasing the possibility of a pipe shortage on the rig. 


It is not all doom and gloom; there are positive lessons to be learned. 

First, it is important to follow the OEM’s inspection procedure. The OEM has knowledge and experience with its products and is committed to ensuring the technology’s success. The manufacturer has no incentive to take unnecessary risks, and its decisions and inspection criteria are based on previous experience and careful risk assessment.  

Our industry has seen high turnover. Green hands now render services and may be more conservative in their practice, as inspection judgments build on experience. There is a natural tendency to lean toward the side of caution and over reject. 

On the flipside, some inspectors, who have experience with the previous premium connection generations, may be unaware of the new inspection criteria for the Delta connection. Using yesterday’s norms does not help. 

When in doubt about the repair numbers, consult the OEM and seek a second opinion. High rejection rates can be a reality, because the rig faced harsh drilling conditions, needed to adjust its running practice, and had self-created damage. In such cases, the second inspection will confirm the results of the first one, and the root causes need to be found elsewhere. Alternatively, we can discover and correct an over-inspection situation and save money by avoiding this second verification. 

Ultimately, the selection of the inspection company needs to prioritize quality over speed and cost, which saves money overall. The idea is not to force the use of equipment in the field that needs repairs but rather to optimize the use of a connection by ensuring it meets the OEM’s criteria. 

About the Authors
Guillaume Plessis
Guillaume Plessis is the senior director for Technical Support for Grant Prideco, a business unit within NOV Wellbore Technologies. He holds degrees in engineering and business management and has more than 25 years of experience in drilling tubulars. He has held various positions, ranging from product engineering to sales and technical support.
Kim Cunningham
Kim Cunningham is the vice president for Tuboscope, a business unit within NOV Wellbore Technologies. He holds an MBA in International Business and Finance from the University of Liverpool and has held various positions in the drilling market for more than 35 years. He is the founder and CEO of CSI Inspection, LLC, which NOV acquired in 2018.
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