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Immingham Storage Co Ltd – Immingham East Terminal
IME-SIS1 - Safety Instrument System Safety Requirement Specification
P & I Design Ltd
DOCUMENT NO: SI277010_RPT
2 Reed Street, Thornaby, UK, TS17 7AF
ISSUE: G DATE: 31.10.14
Tel: + 44 (0)1642 617444
PAGE 9 OF 13
Fax: + 44 (0)1642 616447
www.pidesign.co.uk3.0 General Requirements
The following are general requirements specific to this SIS for prevention of tank overfill.
All safety Instrument functions shall be designed as follows:
De-energise to trip.
Shall operate as a low demand mode system with demands placed on the system from
operations no more frequently than once every 10 years.
Generally in accordance with all the requirements laid down in the standard BS EN 61511.
The response time shall be determined for each storage tank with consideration given to the
import rate and air supply pressure as well as surge pressures created by the closing of the
valves.
There shall be no conceivable individually safe process states which, when occurring
concurrently, can create a separate hazard.
Auto Reset, after high high level activation, of the final element shall not be possible.
The level sensors shall have diagnostics and fault detection on all tanks.
Dominant failure modes of any device shall be to the safe state. The safe state is with the
import valves closed and no flow into the storage tank.
To carry out its design function on loss of electric power or air.
Mean time to repair shall be 72 hours or less.
Valves and actuators will be designed for the following:
o
Adequate margin of safety factor shall be provided for actuators on valves (torque
need to be high enough), nominally 50% over sizing.
o
Import isolation valves do not need to be tight shut off, but be adequate to stop
dangerous flow as well as conforming to antistatic and fire safe requirements.
This system will be installed in mainland UK where it will not be subjected to extremes of
temperature or humidity. We do not consider that
grounding, electromagnetic
interference/radiofrequency interference (EMI/RFI), shock, vibration, electrostatic discharge,
flooding or lightning
will have a detrimental effect on the SIS. The system is designed to fail
safe on any loss of electrical power. The individual elements of the system shall be designed
for the process and operating conditions, the environment and the site electrical area
classification. Specifically, all wetted parts should be suitable for Petroleum Spirit.