January 2016
Oilfield Technology |
57
Figure 8.
5 in. VM165.
Figure 7.
Sour service application.
main material behaviour to improve is the
fracture toughness at temperatures close to
the permafrost, i.e. -76˚F. The main issue
related to this constraint is not necessarily
related to the service temperature while
drilling, but to the potential damages
during ground transportation and handling
in arctic permafrost.
The ductility of steel drill pipe decreases
abruptly below a certain transition
temperature known as the ductile-to-fragile
transition. This particular temperature point
or range is specific to each metallurgy and
grade. Hence, it is desirable to use steel
with the lowest transition temperature
as possible, which becomes a greater
challenge when the steel yield strength
increases. Nevertheless, this transition
temperature has been dramatically
reduced by controlling the way the steel
is manufactured. In particular, the use of
chemistries with a low content of both
phosphorous and sulfur has been prioritised.
Also, a tight control of the steel ‘cleanliness’,
i.e. a reduced content of coarse inclusions
and various oxides tends to prevent the
occurrence of damages. Lastly, chemistries
involving micro-alloying strategies
can successfully lower the transition
temperature. Vallourec continues to develop
solutions for high strength steel grades with
enhanced impact properties at temperatures
as low as -76˚F, on the pipe body, tool joint
and weld zone (VM-135 DP LT).
High strength steel grades
Today’s complex well profiles to be drilled
by drilling contractors and operators, such
as ultra-deep or extended reach wells,
require superior tensile and torsional
performances for drill pipe.
High-strength grades provide greater
tensile strength while maintaining better
impact strength. By using high-strength
material to reduce tube body wall
thickness, lighter drill pipe joints can
be manufactured without compromising mechanical
performance. When tubular with high tensile capacity are
needed for ultra-deep or landing string applications, high-
grade materials offer additional tensile capacity and impact
strength compared to API grades.
Vallourec Drilling Products has been the first
manufacturer to produce and commercialise a grade with
165 ksi minimum yield strength to the industry in 2008. There
are currently several drillstrings and landing strings being
used around the world with such material.
