Jamesbury 3-Piece Ball Valves, Series 4000, Threaded End, Socket Weld, Butt Weld, Rev 2.0, Safety Manual
5
3.5
Random hardware integrity
Tables 1 and 2 below show the reliability numbers based on the Safety Certification for Series 4000 3-piece ball
valves in clean fluid services. The data represent the bare shaft valve, which is one part of the final element.
Using the Metso Nelprof tool, example calculations of the average probability of dangerous failure on demand
(PFD) are shown in Appendix 1.
Note that all the other safety related components of the final element should be included when the reliability
of the final element subsystem is estimated. The analysis must also account for the hardware fault tolerance
and architecture constraints for the complete final element subsystem.
Table 1
Failure rate data with automatic partial stroke test.
Sub system type
A
Diagnostic coverage*
DC[%]
77
Safe Failure Fraction
SFF
N/A**
Dangerous failures
λ
D
[failures / hour]
1.76E-8
Dangerous undetected failures*
λ
DU
[failures / hour]
4.05E-9
Dangerous detected failures, PST*
λ
DD
[failures / hour]
1.36E-8
Safe failures
λ
S
[failures / hour]
2.99E-8
Table 2
Failure rate data without partial stroke test.
Sub system type
A
Diagnostic coverage*
DC[%]
0
Safe Failure Fraction
SFF
N/A*
Dangerous failures
λ
D
[failures / hour]
1.76E -8
Dangerous undetected failures
λ
DU
[failures / hour]
1.76E -8
Dangerous detected failures, PST
λ
DD
[failures / hour]
0
Safe failures
λ
S
[failures / hour]
2.99E-8
* Diagnostic coverage represents common valve – actuator assemblies equipped with an intelligent part stroke device
such as the Neles ValvGuard, The DC value has been used to calculate
λ
DU
and
λ
DD
.
**Safe failure fraction must be assessed for the complete final element assembly.
3.6
Systematic integrity
Systematic integrity requirements according IEC 61508 up to and including Safety Integrety level (SIL) 3 are
fulfilled. These requirements include adequate integrity against systematic errors in the product design, and
controlling systematic failures in the selection and manufacturing process. Series 4000 3-piece ball valves must
not be used in safety integrity functions with higher than the stated SIL level without a proven in use statement
or, in some cases, redundant designs.
3.7
Additional information
Personnel doing the maintenance and testing must be competent to perform the required actions.
All final element components and components shall be operational before startup.
Proof testing should be recorded and documented according to IEC 61508 and maintenance actions done ac-
cording to Part 5.
Unless the procedures above are properly followed, the reliability data shown in Paragraph 3.5 might not be
valid.
