In Refinery we are using Old Boilers made in 1965 with a Design Pressure of 4830 Kpa and Design Temperature of 371 Deg C. Steam drum thickness is 66.7mm where as Muddrum thickness is 51mm. This is high Pressure Boiler used at 4100 Kpa steam. I am doing RBI for Steam Drum and Mud Drum but their is no material information available. Can someone suggest material used for construction during 1965 and Allowable stress value?