a laboratory test for finding out the corrosion resistance

There are a number of ways to do this, but it will be a waste of time.

Corrosion will be more on the order of millimeters per decade at that concentration.

Thanks for your reply.

I am into mechanical seal industry and if i use 316 ss material then cost will be less and if i use duplex ss then cost is going to be high. at this point of time it is very crucial to know about the exact material to be used in the given fluid.

I hope i am clear

Why waste time on something which is undesirable?

Look others have been devising ways to prevent corrosion, methods such as Cathodic Protection and Coatings are commercially being used with success.

Corrosion resistance relates to coatings or effectiveness of CP and not the metal to be protected (stainless steel in your case).

I do not know the answer to your question and I suspect that none will be given. There are significant differences in corrosion rates for static condition compared to flow, turbulence and temperature.

These effects will be localised and not uniform for your vessels and pipes.

Yes, there is such method to find out the corrosion rate of each material in lab, any metallurgy lab can do it for you. If you refer to do it yourself then any book about corrosion subject should give you a hint of how to conduct this test

The corrosion resistance of stainless steels is related more to the pH rather than the level of chloride in the water.

For a neutral water, 50ppm of chloride is to be expected; it would be an unusual potable water if it were any less.

Corrosion rates of 316 in neutral water with 50ppm of chloride is likely to be so low as to be practically negligible. After all, this is what stainless steels were developed for!