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Local Fuel plc - Shoreham Oil Terminal
Safety Instrument System Functional Safety Assessment Stage 5
P & I Design Ltd
DOCUMENT NO: LF364100_RPT
2 Reed Street, Thornaby, UK, TS17 7AF
ISSUE: A DATE: 15.06.2015
Tel: + 44 (0)1642 617444
PAGE 28 OF 32
Fax: + 44 (0)1642 616447
www.pidesign.co.uk5.7
Suitability and Performance of the SIS
5.7.1 Description of Operation
Existing Gasoline Tanks
The SIS is a combination of four (prior to Marine Gas Oil modification) SIF’s albeit they are
interactive with each other in that operation of any sensor results in the final element going to
its safe state. In addition there are eleven other tanks which are fitted with a similar type of
SIL rated sensor and utilise the same logic solver albeit just to provide an alarm. The
description below just relates to the SIF’s on the gasoline tanks, the other tanks utilise the
same technique, however, there is no automatic final element, the operator is warned of
operation of a high high level by annunciation and on the SCADA system, he is then required
to take manual intervention. Annunciation and SCADA repeats are also provided for Tanks
1, 2, 3 & 4.
Each of the four gasoline Tank sensors is connected to a trip amplifier which detects for a
change in mA signal from the sensor, although the device is in effect a switch it provides an
analog output equating to 8mA = Alarm, 16mA = Normal, 22mA = Fault, the trip amplifier is
fitted with two relay output setpoints one at 17mA rising and the other at 15mA falling. Hence,
if the sensor output is not above 15mA and below 17mA then the corresponding relay will
open circuit. A 24Vdc feed is fed into the trip amplifier and through both relay contacts, the
output from the trip amplifier is wired to the coil of a further safety relay via a safety relay
contacts which are operated by the site ESD system. The sensor is fitted with an external test
facility to simulate high level.
Tank 1:
Sensor – Drexelbrook Intellipoint – Tag Number – LE 01
Trip Amplifier – Pepperl & Fuchs KFD2 – Tag Number – LS 01
Safety Relay – PILZ PNOZ-S2 – Tag Number – R252
Tank 2:
Sensor – Drexelbrook Intellipoint – Tag Number – LE 02
Trip Amplifier – Pepperl & Fuchs KFD2 – Tag Number – LS 02
Safety Relay – PILZ PNOZ-S2 – Tag Number – R292
Tank 3:
Sensor – Drexelbrook Intellipoint – Tag Number – LE 03
Trip Amplifier – Pepperl & Fuchs KFD2 – Tag Number – LS 03
Safety Relay – PILZ PNOZ-S2 – Tag Number – R332
Tank 4:
Sensor – Drexelbrook Intellipoint – Tag Number – LE 04
Trip Amplifier – Pepperl & Fuchs KFD2 – Tag Number – LS 04
Safety Relay – PILZ PNOZ-S2 – Tag Number – R372
The final element wiring comprises a 24Vdc feed fed from XV162 Rotork actuator into Tank
1 Safety Relay which has two positively guided contacts per output, the safety function utilises
channel three of the relay. The output from this relay is then fed in series through the safety
relays of Tank 2, 3 and 4 all having two positively guided contacts , the output from Tank 4
safety relay is fed back to the ESD circuit of the Rotork actuator.