But what do in case of floating ground how much common mode voltage is expected in industrial systems ?.
And can you please explain where to tie the shield of the cable in case of 4-20mA loop ?. can we use both chasis ground to tie the shield ? or use the transmitter end common and leave the other end floating .

The only answer I can give to "how much common mode voltage is expected in industrial systems" is "a lot".
The amount is typically related to the age of the plant and, of course, to what is going on in the plant.
A cable shield should be tied to a good ground in one end only. If you tie it in both ends it becomes a ground to ground conductor and actually introduces noise.

I can not give you a theoritical evaluation, only say that with 1/5 gain in the front op-amp and a +-15V op-amp you get a common mode rejection up towards +-75V which has been enough in all cases I have experienced.

The same CMRR can be achieved by other means I am not saying that 1/5 gain and +-15 is the only way.

Erik