Functional Safety 2016

November, 2016 - London

Page 12 of 17

Equipment

Proof Test Method (brief description)

(%)

2. Inspect the Solenoid for dirty or clogged ports and other

physical damages.

3. De-energize the solenoid coil and observe movement of the

actuator and the valve. Energize the solenoid after a small

movement of the valve.

4. Inspect the solenoid for dirt, corrosion or excessive moisture.

Clean if necessary and take corrective actions to properly clean

the air supply. This is done to avoid incipient failures due to dirty

air.

5. Record any failures in your company’s SIF inspection database.

Restore the loop to full operation.

6. Remove the bypass from the safety PLC or otherwise restore

normal operation

Actuator / Ball

Valve

Assembly

A proof test must be performed on the FE at regular intervals. The

actual inspection interval is defined by the reliability report (SIL

calculation) for the specific application. Typically for applications

requiring a SIL3 protection level a yearly proof test interval is used.

To carry out the proof test, proceed as follows.

1. Ensure that all flow through the valve is stopped or verify that

stopping the flow during the test will not cause operational

problems.

2. Perform the actions as per the Monthly inspection.

3. a) Solenoids: De-energise solenoid (one at the time) thus

initiating the valve to go to the fail safe position. Verify during

closure whether all parts of the sub-system function properly

(like the quick exhausts, did they all respond?). Assure that the

time between de-energising and full closure (or opening) is

measured. Repeat 3 times. Repeat for each solenoid. Verify

whether these timings falls within the maximum permissible

time. Compare with previous measurements and in case of big

differences contact Mokveld.

b) Mechanical initiators: As above however the trigger is not de-

energising the solenoid but creating a high pressure (above

~95%