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| APPLICATION |
Instrumented
Protection Systems – HIPPS, High
Integrity Pressure Protection Systems |
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Company |
Mokveld
Valves B.V. |
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Page
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2
of 6 |
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Copyright
2002 Mokveld Valves B.V. All rights
reserved. |
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Technical information
and illustrations included are subject
to changes without notice. |
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| What
is HIPPS |
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In HIPPS, instruments provide the safety
function. The Safety Loop consists of
one or more initiators, final elements
and a logic solver.
Either completely mechanical components
or a combination of mechanical and electrical
components can be used. All components
shall be fail-safe in the de-energised
mode.
With HIPPS, the protection against overpressure
is obtained by quickly isolating the
source causing the overpressure, reducing
the plant’s risk profile. |
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| Standards
& Design Practices |
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The enormous flow rates that are currently
being processed in combination with
the environmental constraints initiated
the widespread and rapid acceptance
of HIPPS as the ultimate protection
system. The International Electrotechnical
Commission (IEC) has followed up on
these developments by introducing the
IEC 61508 standard. This is a performance
based, non-prescriptive standard, which
provides a detailed framework and a
life-cycle approach for the design,
implementation and management of safety
systems applicable to a variety of sectors
with different levels of risk definition.
A consistent basis in reducing the probability
of a hazardous event is applied. It
is defined as a unction of the risk
that a process will exceed its safety
limits multiplied by the probability
that the safety system will fail on
demand (PFD).
Although this Standard is mainly focused
on Electrical/Electronic/Programmable
Electronic Safety-related systems, it
also provides a framework for safety-related
systems based on other technologies
including mechanical systems.
The basis for using instruments in safety
functions are four Safety Integrity
Levels (SIL) representing the necessary
risk reduction as recognised in a risk
analysis. Each SIL level corresponds
with a tolerable Probability of Failure
on a Demand (PFD). The entire safety
loop, including the safety function,
shall meet this PFD value. |
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The German DIN 3381 standard, dictating
qualitative requirements as well
as
some quantitative requirements for
safety shut-off valves has been
used for the
past decades in (mechanically) instrumented
overpressure protection systems.
Along
with leakage rates, response times
and accuracy levels, this standard
also
specifies safety factors for the material
quality and over-sizing of the driving
force closing the final element. Independent
design verification and testing
to prove
compliance to the DIN 3381 standard
is mandatory. This resulted in an
inherently
safer product as illustrated by Mokveld
HIPPS valves build in accordance
to
DIN 3381 with a failure rate (λ)
as low as 2, 64 E-4 per year in clean
service and 3,3 E-4 for unclean service. |
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