Functional Safety 2016
November, 2016 - London
Page 13 of 17
Equipment
Proof Test Method (brief description)
C
PT
(%)
setpoint) of the initiator. Or push the test button to test only the
FE and not the mechanical initiator. For verification of the
mechanical initiator refer to the specific Installation, Operation
and Maintenance Instructions and Safety Manual. If other
sensors monitor the system safety, these must be tested.
4. Check each time that the valve is completely closed or opened
when required. If possible, drain the downstream part of the line
and verify that the valve does not leak when closed.
Even when following the vendor requirements stipulated within the equipment safety manuals, it
can be seen that none of the vendors claim to have 100% proof test coverage. It is also
important to note that in each of the Safety Manual requirements the vendor makes the
assumption that the proof test is carried out by a competent person. They take no further claim
for systematic capability of the end-user.
Taking the assumption that so far as is reasonably practicable the systematic requirements for
the proof test coverage have been adopted, the table below illustrates how to incorporate the
prescribed proof test coverage factors into the calculations and demonstrates how the C
PT
and
corrected PFD
AVG
impacts on the SIS risk reduction requirements.
Note:
Systematic Requirements for the proof test coverage are that a competent person has accurately specified
the SIS, a competent engineer has design the system to permit all requirements of the proof test to be conducted,
a competent person has developed the proof test incorporating all the above requirements from the relevant safety
manual, a competent person has conducted the proof test and a second competent person verifying the proof test
has been conducted as prescribed.