I want to impose a specific hanger cold load to a piping system for preventing overload of equipment nozzle.
How I can estimate spring rate? and basically can I specify a cold load and calculate the spring rate myself or we should just use the spring rate and cold load that CEASAR specify?

You really can't specify a spring rate. You are going to be limited to the standard spring designs available from the major vendors.

In the spring specification window, you can input the spring rate and cold load that you want the model to use. You usually get this out of a catalog.

I believe the real question here is how does one size a spring, as opposed to letting the program automatically size it. If this is the case, I suggest reading the CAESAR literature for the spring sizing methodology.

If that is not the case, Mr. Klein is correct. Vendors use specific spring rates for their products. Its a good idea to know the vendor who will provide the springs, so the correct database within CAESAR may be used. Otherwise, make sure the "or equal" clause is in the purchase order.