585 / 1143
16
©ABBGroup
October23,2016|Slide31
HFT using 61511 Table – the Ed 2 way
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61511 Ed 2 HFT requirements in clause 11.4
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No mention of ‘Prior Use’ for HFT in this clause
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But……..
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To demonstrate that the proposed or installed safety instrumented function
meets the target SIL, three criteria must be met: -
1.
Control of Random Hardware Failures – these are the PFDavg
calculations
2.
Meet Architectural Constraints – Hardware Fault Tolerance
3.
Control of Systematic Faults
©ABBGroup
October23,2016|Slide32
HFT using 61511 Table – the Ed 2 way
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Clause 11.9, Quantification of random failure (the PFDavg calculations)
requires the reliability data to be ‘credible, traceable, documented , justified
and shall be
based on field feedback from similar devices in similar
operating environment’
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Clause 11.5, Requirements for selection of devices, uses ‘Prior Use’, but in
relation to control of systematic failures, again demonstrating the
performance of the device in
similar operating environments and the
volume of operating experience
.
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So for SIL 2, HFT 0 is only applicable if these requirements are met
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They look a lot like the Ed 1 Prior Use requirements