We are looking to hot tap / cut a 14.75" diameter hole in 304H SS flat material (7/8" thick) that is operating at 700F-1000F. We are using a 400F steam purge on the cutter side of the blind flange to cool. We have attempted several mock-ups to fine tune the procedure before going to the field. We were successful at cutting 1/4" thick 304H plate even though the pilot hole was driven off-center. When attempted again on another mock-up with 304L plate, the pilot was driven off-center and the hole cutter vibrated severely and we only cold work hardened the stainless. No further machining progress was made. The mock-ups have used stress relieving blankets at 850 - 1024F around the periphery to simulate the field conditions. We are only using a tool steel for the cutter teeth. The 14.75" cutter had 15 teeth and we are questioning whether less teeth would be preferable. We are using the TDW 1200 series tapping machine at 18 rpm in dual drive mode (which is the slowest). Tool steel is being used because there is concern that carbide tips would melt off at elevated temps.
Any comments about allowable temps for carbide tips, cutting speed, cutter tip angle, or other tips to avoid cold working 304L/304H stainless would be appreciated.
Any comments about allowable temps for carbide tips, cutting speed, cutter tip angle, or other tips to avoid cold working 304L/304H stainless would be appreciated.
