Invinci,
Check out this thread
thread798-188767
In my opinion, if the steam is not going into a liquid level, then there is little need for a sparger with sized holes and all. Rather than a "sparger" you just need to break the momentum of the steam to avoid impingement problems.
If sparging steam into a liquid, then consider getting something already available (see example in thread). This "home-made" approach of sizing a sparge pipe is not always that much savings in the long run, and if it has problems then it can cost you far more than the initial savings.
best wishes,
sshep