Hi Vdao

1) The welding filler metal "classification" is a supplementary essential variable. If the PQR test was done with an ER316L filler, a change to ER316 would constitute a change in "classification". Thus, you will need to re-qualify.
2) If the application as described in the design and fabrication code does not require you to perform impact testing, you can use the same PQR (which has the impact testing) and draw up a different WPS for applications without impact testing in which you may change the classification of the filler metal.
3) The restriction on using 316L on 316 base metal will not be due to corrosion concerns, because generally 316L would display better corrosion resistance than 316. The concern is usually that the 316 is specified because it has better high temperature properties, and the customer is concerned that the use of 316L filler will make the weld under strength at these elevated temperatures. Hence the requirement on using 316 filler. Generally if this is the case, then low temperature impact properties would in any case not be a concern, so the supplementary essential variables will not be specified.

Regards
Niekie