MTFB & Service Life

[mad4x4]

If you look up a Siemens analog card such as 6ES7331-7KF02-0AB0 the MTFB is quoted at 19.6Y. (https://support.industry.siemens.com/cs/document/16818490/mean-time-between-failures-(mtbf)-list-for-simatic-products?dti=0&lc=en-WW)
But in real terms, in a harsh environment ( 40Deg C +95% humidity), what would you expect the Service Life to be?

Is there a quoted recommended service life from Siemens or an engineers rule of thumb? I would be saying that after 15years, we should be starting a changeout program even if it is like for like or considering an upgrade due to obsolescence.

 

[JesperMP]

40 °C and below condensation does not sound that harsh to me.
In that case, the life expectancy should be as stated by Siemens.

Maybe you mean that the ambient temperature is 40 °C, and the temperature inside the control cabinets is significantly higher. If so, you need to establish the what are the actual temparature where the modules are installed.
I am unaware of a lifetime derating for electronic modules based on temperature.
If it turns out that the temperature is high at the electronic modules, then I would take steps to counter the high temperature.

S7-300 is quite solid IMO. After S7-300 end of life time announcement - which is rumored to come in 2022, the S7-300 will have a long support time - 10 years - where spares can be purchased, but count on that spares part prices will increase. I would not be in a hurry to replace the S7-300 in a running system.

 

[mad4x4]

The harsh environment is that the equipment is mounted in a marine environment with 95-100% humidity outside the cabinet, no ventilation and the cabinet is significantly warmer than the external environment. AIr will have a high saline content.

All the RIO is mounted in an IP55 cabinet and is mounted with the trunking very close about 10mm from the top of the cards, trunking would be about 80% full leaving very little airflow.

We recently had a failure reported as "Burnt out" analog card and we are trying to work out the cause and if we should consider changing other cards as a preventative measure. We know the MTFB is 19y, but what is the realistic life expectancy of an analogue (4-20mA) card. We may already change out components like PSUs every 10years to prevent premature failure.

In the Oil and Gas industry, we design everything (mechanical) with a 25Year life expectancy and we know computer Operating system probably have a 10 Year life. But should we be putting a life expectancy on our solid-state controls>

 

[JesperMP]

Marine environment with salt in the air. That is a special case and I would assume that only electronics with conformal coating should be used.
Regular electronics that are not suited for such an environment should not used. For S7-300 it should be the SIPLUS variant which have both conformal coating and a wider temperature range.
It is impossible to guesstimate how long regular electronics will survive in such an environment.