American Oil and Gas Reporter - September 2016 - 84

SpecialReport: Tubulars Technology
yond those conditions, the next step is to
use a nickel-based alloy, which is expensive and difficult to machine.
The C72900 alloy machines faster
than even free-cutting steel, with less
tool wear, meaning the components cost
less. Typically, other types of metal need
to be machined into their primary mill
form geometries (such as a hollow bar),
which is a process that can prove to be
more expensive than the material itself.
However, there are data that indicate
the performance gap can be filled with a
material such as the enhanced C72900.
Although not generally suitable for HP/HT
installations, using C72900 in the 90 percent of applications that are mildly to
moderately sour is worthy of further
study. Where 13-Cr steel cannot be used,
and it is not technically necessary to use
a nickel-based alloy, it is possible that
C72900 tempers may prove adequate performance-wise and at lower component
cost.
More permanent applications for
C72900 are being considered now that
these tempers are being manufactured
with adequate toughness and ductility at
the required strength levels.
One example of applications in downhole drilling and logging tools is Houston-based Compass Directional Guidance
Inc., which is using 13⁄8-inch outside diameter tubes of the copper-nickel-tin
alloy to build slim-hole measurementwhile-drilling tools for ultradeep wells.
The slim-hole tools have pressure tolerances up to 25,000 psi and can be run

with 27⁄8-inch OD mud motors and collars,
rather than the more typical 20,000-psi,
31⁄2-inch MWD tools.
The 13⁄8-inch tubes are utilized to make
all the housings containing the sensitive
electronics and sensors of the slim-hole
MWD tools. A number of challenging
drilling environments are suitable for this
technology, but one application is the
Terim oil field in Northwest China, where
Compass Directional Guidance's systems
are being run in wells more than 22,000
feet deep.
A9 Manufacturing is a precision machining shop that fabricates downhole
tools, including Compass Directional
Guidance's 1.375-inch slim-hole MWD
system. After having issues with the pressure barrel's high-temperature performance
requirements when produced from copper
beryllium (CuBe), A9 and Compass decided to try one of the copper-nickel-tin
alloy tempers. It was easy to machine,
and after running the slim-hole MWD
system down hole, its resistance to erosion
and stress cracking proved superior to
high-temperature CuBe while maintaining
similar resistance to galled connections
(the industry traditionally has relied on
CuBe for resistance to galled connections).
Larger-Diameter Capability
In the metals industry, it is always
challenging to achieve good properties-
both longitudinal and transverse-all the
way across the diameter of a piece of
metal that is, for example, seven inches

FIGURE 2
Typical Anisotropy of New C72900 Tempers
Ultimate Tensile Strength Anisotropy
13% Difference

ksi

160
140
120
100
80
60
40
20
0

Ultimate Strength-T

3 4 5 6
Specimen Pair

Yield Strength Anisotropy
20% Difference
Yield Strength-L

Yield Strength-T

3 4 5 6
Specimen Pair

% in 4-D

140
120
100
80
60
40
20
0

Ultimate Strength-L

84 THE AMERICAN OIL & GAS REPORTER

Elongation
Anisotropy
13%
Difference

15
Elongation-L

Elongation-T

5
0

0 1 2 3 4 5 6 7 8
Specimen Pair

in diameter, as well as across its entire
length. Some of the components that are
being constructed from the new tempers
are significantly larger in diameter.
Anisotropy of mechanical properties is
typical in large section bars.
Anisotropy is a material's directional
dependence to mechanical properties. For
example, wood is naturally anisotropic
because its strength, hardness and other
properties differ when measured in different orientations (with or against the
grain). Fortunately, as shown in Figure
2, this phenomenon is both minimal and
consistent in the new C72900 tempers.
The tempers may be manufactured as
hollow bars directly off the mill, eliminating the need to machine the core from
a solid bar, which offers significant cost
savings. Alternative materials typically
come from the mill as a solid bar, and
must be trepanned or gun-drilled in order
to convert them into a hollow bar (the
form taken by most large-diameter components), which is very expensive and
wasteful.
The industry continues to demand
high-strength, corrosion-resistant materials
that are not susceptible to hydrogen embrittlement. The C72900 tempers are a
prime example of how materials engineers
are developing new alloys that can be
economically mass produced to meet the
industry's demands.
Expert engineers and scientists in metallurgy and materials are continually
pushing the boundaries of advanced material solutions. The keys to future technology development are for material engineers to remain "tuned in" to what the
industry is searching for, invest in dedicated research and development programs,
and conduct experiments in production
facilities, since tests conducted in the
laboratory often do not translate to events
that can occur in real life.
In today's economic environment, it
is not only technical challenges that operators are trying to solve. It is certainly a
different world now, and providing economic savings is crucial. Service companies
and operating companies alike still need
optimal performance, but they also need
the total cost of ownership of an asset to
be as low as possible without sacrificing
performance. Many times, design changes
alone will not achieve both requirements.
Materials engineering changes are needed
as well, and often are the most important
part of the solution.
Questions need to be asked, such as

American Oil and Gas Reporter - September 2016

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