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
GUILLAUME PLESSIS and
KIM CUNNINGHAM, NOV
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
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:
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).
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
We were confident that this would be the norm until owners
reported higher numbers. An investigation revealed that:
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
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. Figure 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
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. WO
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
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.