Working on a flange analysis. Can we include nylon Gasket in static simulation?

if the nylon is small displacement, in the linear range of the material, should not need nonlinear analysis

but in the real world, these are assumptions, the real world is nonlinear and transient

"Need to check the strength of the both flange while in operation."

Can you provide more detail on what you mean by this? Are you wanting to calculate the loads on the bolts? The stress in the flanges?

"so my question is can I use the use nylon gasket properties in static analysis.Will it work Or do i have to go for non-linear anlysis."

A static analysis means that the results are independent of time (as opposed to a dynamic analysis where the results are dependent on time). As such, you can have linear and non-linear static analyses (and linear and non-linear dynamic analyses).

You problem is a static one most likely, so the only question is whether a linear approximation is good enough. It's hard to say with the information you've provided whether this is the case or not. However, if you end up needing to capture contact, large strains, and/or a hyperelastic material model, then you'll need to do a non-linear analysis. Whether you need to capture these effects depends on what you're after results wise.