Hydrocarbon Processing - August 2022 - 67

Gas Processing & LNG Industry Spotlight
be used in safety-critical applications, such
as in an LNG high-integrity pressure protection
system (HIPPS) and with various
safety interlock and shutdown services.
Meeting the challenge. An FLNG design
firm issued a proposal request for three
24-in., Class 900 safety shutdown valves to
meet very demanding requirements for
physical size, torque, speed of response and
environmental conditions. The actuator
torque had to be 1.5 times the maximum
torque required for the valve, and since
the valves were part of a HIPPS installation,
each valve assembly required a SIL
3 rating. The performance specification
required the valves to stroke from 100%
to 20% in less than 4 sec, and then to close
the remaining 20% in an additional 4 sec to
avoid damaging the valve seat. The entire
assembly had to be painted and coated for
an offshore marine environment.
After evaluating the options, actuators
utilizing helical-slot designs were
chosen due to the dramatically reduced
valve footprint. These proprietary helical-slot
actuatorsa
were paired with SILrated
digital valve controllers to provide
remote health monitoring and advanced
diagnostics (FIG. 6).
The torque requirements were easily
met with the standard actuator design,
but the stroke requirements required a
modified integral quick exhaust valve that
could achieve the initial stroke time yet
gradually close the valve as it approached
the end of the stroke (FIG. 7). A customized
quick exhaust valve utilized a damper
with two bypass valves to adjust the end of
travel performance as necessary to meet
the required stroke timing and profile.
The entire valve assembly was certified
to a safety rating of SIL 3, and it was
painted and coated appropriately to meet
the difficult marine environmental conditions.
The assembled valves were fully
tested and certified during a field acceptance
test and are operating in an FLNG
production platform in the middle of the
Indian Ocean.
Takeaway. The proprietary actuatora
can
be customized to achieve specific torque
and movement profiles and paired with
high-performance digital valve controllers
as part of a highly reliable, safety-rated
valve assembly suitable for SIL 3 applications.
The actuator speed of response and
closing profile can also be altered to meet
very demanding actuating specifications,
and it can be adjusted to provide a " soft
close " final stroke.
When faced with very demanding
space constraints in piping manifolds,
process skids, or offshore floating oil and
gas production facilities, helical-slot actuators
are often the best choice. They can
match the torque and speed of response
of scotch yoke and/or rack-and-pinion
actuators, yet their vertical profile offers
significant equipment and piping design
advantages. This greatly reduced footprint
enables the valves to be placed much
closer together or positioned near walls
or tanks, yet still be accessible for maintenance
in either case.
NOTE
a Biffi TPS helical-slot actuators
MILAN RAKITA is an Associate Product Manager
for pneumatic and hydraulic actuators at Emerson's
Automation Solutions business. In this role, he
works with end users and Emerson experts to
develop product roadmaps, including new product
development and value engineering. Mr. Rakita earned
a degree in general management from the Università
Cattolica del Sacro Cuore in Milan, Italy.
FIG. 6. Three SIL 3-rated, 24-in., Class 900 safety shutdown valves undergo testing
for an FLNG safety-critical shutdown application.
FIG. 7. A customized quick exhaust valve is utilized to quickly close the valve to minimum flow,
and to then adjust the speed of the final closure to avoid process pressure surges.
Hydrocarbon Processing | AUGUST 2022 67

Hydrocarbon Processing - August 2022

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