Flowserve MX Electronic Actuator SIL Safety IOM - Manual (Page 16)

Limitorque MX Electronic Actuator FCD LMENIM2350-01 – 9/13
16
FLOWSERVE PROPRIETARY INFORMATION
Use or disclosure of this information is subject to the restrictions on the title page of this document
6
MXa Safety
6.1 Basic board set
Table 6.1 - PFD
avg
for MXa Actuator without PST
Proof Test Interval
Mission Time 1 year 3 years 5 years
10 yr 5.24 E-3 1.28 E-2 2.18 E-2
15 yr 5.45 E-3 1.38 E-2 2.20 E-2
20 yr 5.66 E-3 1.36 E-2 2.23 E-2
6.2 PFDavg for MXa Actuator with PST
Table 6.2 - PFD
avg
for MXa Actuator With Monthly PST
Proof Test Interval
Mission Time 1 year 3 years 5 years
10 yr 2.96 E-3 5.93 E-3 9.52 E-3
15 yr 3.22 E-3 6.51 E-3 9.77 E-3
20 yr 3.47 E-3 6.60 E-3 1.00 E-2
Referring back to Table 2, repeated here for convenience, one can assess the SIL capability of an SIF that incorporates
an MXa actuator as a component in a SIL-2 SIF control loop.
SIL PDF RFF
4 10 5 … < 10 4 10,000 to 100,000
3 10 4 … < 10 3 1,000 to 10,000
2 10 3 … < 10 2 100 to 1000
1 10 2 … < 10 1 10 to 100
Example 1: Deploying an MXa in a One out to One [1oo1] configuration for an expected mission life of 10 years, and
that is not expected to be required to perform its Safety Function more than twice per Proof Test Interval (low demand
mode), and having a full Proof test no less frequently than once per year, it can be seen that the PFDavg is 0.00524.
This PFDavg value falls between the allowable limits for SIL 2: 0.01 > 0.00524 > 0.001.