Functional Safety 2016

November, 2016 - London

Page 9 of 17

The Figure 1 shows a generic HIPPS SIS, commonly used in downstream natural gas

processing facilities.

The SIS is comprised of a 2oo3 architecture, for the pressure sensor sub system, set to initiate

a trip signal to the logic solver when 70barg is detected from upstream. The trip signal from the

logic solver de-engerises either of the two soleniod valves to relieve the air pressure in the

pneumatic actuator, which will drive the valve closed (Air Fail Closed) within a total response

time of 3 seconds. The final element is classified with a zero leakage rate (API 6D Rate A).

The equipment specification is as follows: -

•

Sensors – Smart Pressure Transmitter (two wire 4-20mA) voted 2oo3.

•

Logic Solver – Solid State triplicated fail safe logic with Namur 43 compliant trip

amplifiers.

•

Solenoid Valves – 3 way 2 position normally closed 24 vdc Electro Magnetic with spring

return voted 1oo2.

•

Final Element Valve – Mokveld Valve B.V., RZD-R including M-series actuator.

A simplified proof test methodology is described in Table 3, typically in line with a manufacturers

Safety Manual, withextracts of test requirements taken from the vendor requirements, to

demonstrate an example of how to approximate C

and the actual impact on the corrected

PFD

AVG

for the SIS.

Table 3: Basic simple HIPPs proof test methodology

Equipment

Proof Test Method (brief description)

(%)

Sensor

(incl Impulse

line)

This test detects approx. 99% of the possible dangerous undetected

device failures.

1. Bypass safety PLC or take other suitable measures to

prevent alarms from being triggered by mistake.

2. Disable locking ("Locking/Unlocking", ® ä 46).

3. Set the current output of the transmitter to HI alarm via a

HART command or by means of the onsite display and check

whether the analog current signal reaches this value.

•

e.g. simulate an alarm by means of the SIMULATION MODE

and SIM. ERROR NO. parameters. This test detects

~99%