Annex C(informative)

Calculating or evaluating MTTFd values for single components

C.1 General

Annex C gives several methods for calculating or evaluating MTTFd values for single components: the method given in C.2. is based on the respect of good engineering practices for the different kinds of components that given in C.3 is applicable to hydraulic components; C.4 provides a means of calculating the MTTFd of pneumatic, mechanical  and electromechanical components from B10 (see C4.1); C.5  lists MTTFo values for electrical components.

C. 2 Good engineering practices method

If the following criteria are met，the MTTFo or B10D value for a component can be estimated according
to Table C.1

a〕 The components  are manufactured  according to basic and well-tried  safety principles  in accordance with  I SO 13849-2:2012, or the relevant standard ﹛see Table C.1) for the design of the component 〔confirmation in the data sheet of the component).

NOTE       This information can be found in the data sheet of the compon ent manufacturer.

b)  The manufacturer of the component specifies the appropriate application and operating conditions
for the SRP/CS designer.

c) The  design  of  the  SRP CS  fulfils  the  basic  and  well-tried   safety  principles  accord ing  to ISO 13849-2:2012, for the implementation and operation of the component.

C. 3 Hydraulic components

If the following criteria are met，the MTTFo value for a single hydraulic component, e.g. valve, can be estimated  at 150 years.

a) The hydraulic components are manufactured according to basic and well-tried safety principles in accordance with ISO 13849-2:2012, Tables C.1 and C.2, for the design of the hydraulic component (confirmation in the data sheet of the component).

NOTE       This information can be found in the data sheet of the component manufacturer.

b) The manufacturer of the hydraulic component specifies the appropriate applicat ion and  operating condit ions for the SR P/CS designer. The SRP/CS designer shall provide i nformation pertaining to his responsibi lity to apply th e basic and well-tried safety pr i nciples accord i ng to I SO 13849-2:2012, Tables C.1 and C.2, for the implementation and operation of th e hydraulic component.

If the criteria presented in C.4 : are met, the MTTFo value for a single hydraulic component, e.g. valve, can be estimated  at 150 years. I f the mean number of annua l  operations 〔nop〕 is below 1000 000, then
the MTTFo va lue can be estim ated higher as shown in Table C.1

But if either a）or b) is not achieved, the MTTFo value for the single hydraulic component has to be given by the manufacturer. Instead of using a fixed value for the MTTFo as described  above it is permissible to use the B10D-concept for MTTFo of pneumatic , mechanical and electromechanical components also for hydraulic components if the manufacturer can provide data.

Table C.1- lnternational Standards dealing with MTTFo or B10dfor components