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Engineering & Construction
Alloy K-500 – Past Failures in Downhole Completion Tools
a report by
Karthik Krishnan, Joshua Rooker and Greg B Chitwood
Materials Science Department, Halliburton, Carollton, Texas
Since the early 1900s, the marine and chemical industries have relied extend the limits to 100kPa maximum H
2
S and 50,000mg/l maximum
on the extensive use of corrosion-resistant alloys. Early testing and chloride at a minimum pH of 4.6; however, it too was not passed.
experience of nickel–copper alloys revealed them to be highly During the Maintenance Panel meetings, it was believed that the
resistant to corrosion in these applications. Developed from the failures were related to material coming from one low-quality source,
family of nickel–copper alloys, Alloy K-500 (a nickel–copper perhaps with inferior melt practices and residual work from mill-
precipitation hardenable alloy) gained widespread use as the working operations. Many details were missing, however, prompting
material of choice for boat shafts and marine bolting because it Halliburton scientists to perform a more detailed investigation.
could be heat-treated to high strength and hardness.
This article briefly describes the review of case histories of Alloy
The corrosion resistance and widespread availability of Alloy K-500 K-500 in order to evaluate the newly proposed limits and hypotheses
placed the metal among the first nickel-based alloys to be used in oil discussed in the Maintenance Panel meeting. For a more detailed report
and gas wells. While many steels demonstrated high rates of failure on the investigation into the failures of Alloy K-500, refer to reference 12.
during laboratory testing in environments saturated with H
2
S
(equivalent to the present-day National Association of Corrosion Field Failures of Alloy K-500
Engineers [NACE] TM0177 ‘Solution A’ test), Alloy K-500 was Records show that failures of Alloy K-500 occurred in both oil- and
successful under the same conditions.
1,2
Early field experience with gas-producing wells and in such geographically diverse locations as
Alloy K-500 proved highly successful in environments containing H
2
S.
3
the Middle East, North America and South-East Asia. The
Because of its ability to resist sulphide stress cracking, the first edition environments in which the failures occurred are provided in Table 1.
of NACE MR0175 allowed the use of Alloy K-500 in sour environments
containing any level of H
2
S as long as it was annealed, annealed plus The downhole tools that experienced failures in the environments
age-hardened or hot-finished plus age-hardened to a maximum included components located shallow in the wells, such as
hardness of 35HRC. Wellhead stem failures of Alloy K-5004 were subsurface safety valves and safety valve landing nipples (in
reported around the time of publication of the first edition of NACE environments 1 and 3), as well as components set near-bottomhole,
MR0175, but were concluded to be from hydrogen embrittlement (HE),
which was isolated to low-temperature conditions common to
Karthik Krishnan is a Metallurgist in the Materials
wellhead applications. As a result, Alloy K-500 continued as the
Science Department at Halliburton in Carrollton,
primary candidate for sour service applications for downhole tools.
Texas. Prior to joining Halliburton, he worked as a
Scientist at Tata Research Development and Design
Centre in Pune, India for four years in the Thermal
Because of the Alloy K-500 failures observed during material analysis Processing of Materials Group. He holds a BTech in
over 20 years ago, Halliburton became suspect of the material and
metallurgical engineering and materials science
from the Indian Institute of Technology in Bombay,
was diligent in evaluating its performance. Indeed, several failures of
India and an MSc in materials science and
downhole tools made from Alloy K-500 occurred until the mid- engineering from Case Western Reserve University
1980s. These failures led Halliburton to no longer endorse the use of
in Cleveland, Ohio.
Alloy K-500, instead turning to the newly introduced UNS N09925
(Alloy 925), which was more economical to use and proved even
Joshua Rooker is a Metallurgist in the Materials
more resistant to hydrogen damage.
Science Department at Halliburton in Carrollton,
Texas. He holds a BSc in metallurgical and
materials engineering from the University of
Reported failures
5–8
led to the restricted use of Alloy K-500 to a H
Alabama in Tuscaloosa.
2
S
maximum partial pressure of 3.45kPa and a minimum pH of 4.5 when
NACE MR0175 was re-written and published in 2003.
9,10
The new
limits of service for K-500 were not accepted throughout the industry
as many felt that the new limits placed on the metal were too
Greg B Chitwood is a Metallurgist and Materials Team
restrictive. A joint industry project (JIP) was therefore established with
Leader in the Materials Science Department at
Halliburton in Carrollton, Texas. He is an active
the aim of extending the current limits in NACE MR0175 by testing
member of the National Association of Corrosion
Alloy K-500 outside the limits and investigating the published failures.
11 Engineers (NACE), receiving the Presidential
Achievement Award in 2005 for his contribution to
Two ballots were proposed. The first ballot attempted to extend the
the NACE/ISO standard MR0175/15156, and he chairs
limits to 689kPa maximum H
2
S and 50,000mg/l maximum chloride at the ISO 15156 Maintenance Panel for this important
a minimum pH of 3.5, but was rejected by the NACE Maintenance
industry standard. He holds a BSc in metallurgical
engineering from the Colorado School of Mines.
Panel Committee in 2006. The second ballot, in 2007, proposed to
© TOUCH BRIEFINGS 2009
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