How often shoud I change the sport springs?10 points immediately?

I wonder how can I know that my 40mm lowered springs is damaged and need to be changed?

What is the normal life time of these springs?

I'm fitting mine with the standard dampers.How often shoud I change the sport springs?10 points immediately?
The only real way to tell is to remove the spring and have it load tested.

If you measure you ride height after the installation of a new spring then you should never have more then a 15% less reading in a measurement after normal wear and tear.

You should also jack it up and give a good visual inspection of the spring, looking for cracks or a difference in the distance between coils.

A bad shock would also be a thing to look at, it the shock has failed or you can see sighns of leaking oil from it, it may be bottoming out and giving you the feeling of a broken spring.