I have been instructed to use a WPS that indicates 1/2" fillet weld that has a base metal range from 3/4" to 2 1/2" in thickness that is A36 steel. Using E7018 with a preheat of 150 degrees minimum and 550 maximum interpass. The WPS calls for a 30 minute soak time. Can some one explain this soak time as I am not familiar with it? Thanks.