independent, self-contained power
source, the actuator can perform this
duty when mains power is not available
or when the loss of mains power triggers
the immediate failsafe operation of the
valve. Consequently, and combined with
its suitability for installation in remote
locations, many end users see the main
function of the gas-over-oil actuator on
a pipeline as being the reliable provision
of precautionary and emergency shutdown and isolation duties in the event of
a line break or similar event.
Emergency shutdown, however, is
just one of the many duties the actuator
may be specified to perform. Virtually
all pipeline applications demand a control package specification that is customized to some degree, so the actuator
must be capable of meeting a diverse
range of control and instrumentation
requirements without excessive re-engi-neering.
One solution is to engineer a multi-
Your Pipeline to
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function manifold block at the center of
the gas-over-oil system, which integrates both the gas and hydraulic functions in order to meet a wide variety of
the control functions that are likely to
be specified. These include, for example,
altering the speed of valve travel, which
may be required very quickly in an
emergency but much more slowly to prevent damage to the pipeline during routine operations or partial stroking maintenance programs. Valve operation can
also be preset to activate when a set
point pressure drop value is signalled, or
from other data provided locally or
remotely.
In addition, individual gas company
approvals may need to be obtained. In
Russia the GOST certificate of conformity and federal use permit is required.
Similarly, ENAGAS, the Spanish gas
pipework network operator, and SNAM,
the Italian equivalent, require approvals.
In both cases, two examples of actuators
are required to be subjected to an arduous program, as this summary of the
main SNAM test illustrates:
Dimensional check of actuator
components before assembly
Pressure test on piston, hydraulic
circuit and pneumatic circuit
Dielectric strength test on the
main electrical components
Stroke time regulation and verification
Static torque test
Dynamic torque recording at 195
psi (13bar-g), 375 psi (25bar-g),
750 psi (50bar-g) and 1050 psi
(70bar-g)
Strain test on main components at
1200 psi (80bar-g)
5 cycles with remote control at
25%, 50%, 75% and 100% of the
maximum torque
5 cycles with manual control at
25%, 50%, 75% and 100% of the
maximum torque
Torque Limiting Device verification test (see below)
Low temperature test at - 4˚ F
(- 20˚ C) (functional test and
torque limiting device verification
test)
