Is there any real case or study or paper where I can find a comparison between the reliability in classic hardwired I/O system(Junction box-marshalling-Controller) and field bus system.

Many customer do not like to take risk in change their way to do the thing....it?s obvious, it?s better safe than sorry.....

I am not talking about safety loops.(ESD)

In addition is there any cost study (installation safe money, etc)....

Which fieldbus are you referring?  Foundation Fieldbus, Profibus, others?

Emerson has many cases on cost savings for Foundation Fieldbus.  Just be careful....they don't tell you everything.

For example, we found that while there were savings in installation, the engineering was more expensive (more time to design), the instrumentation is more expensive, commissioning time was greater (despite what the sales rep indicates) and maintenance of the system is done by engineers instead of the technicians (much more costly).  Again, this was our experience on two installations.  Other outcomes may vary.....

The comparisons in manufacturer's literature are against standard 4-20mA instrumentation.  If you compare it against HART, then the difference between the systems is much less.

I have not seen any papers on reliability.  We have had no issues in the 5 years of service using Foundation Fieldbus.

They are extremely reliable and for all practical purposes might even be ignored completely when analyzing reliability issues in any plant.  Unless the electronics are exposed to ambient conditions outside their design specs, the actuators, valve() and virtually all other types of equipment will have failure rates many orders of magnitude greater than the control electronics.  It is actually safe (within all reason) to ignore their contribution to unreliability issues when taken in conjunction with almost any additional components.

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