- MATERIAL S355JOWP (CORTEN-A) EXCEPT OTHERWISE INDICATED.- PAINTING EXTERNAL: ONLY FOR MATL. S275JO. UNINSULATED CARBON STEEL SURFACES WITH OPERATING TEMPERATURE TO 80°c- PAINTING INTERNAL: ONLY FOR MATL. S275JO. UNINSULATED CARBON STEEL SURFACES WITH OPERATING TEMPERATURE TO 80°c BUT SAND BLASTING AND PRIMER ONLY - WELDING: CONTINUOUS FILLED WELDING FULL PENETRATION FOR FLANGES AND SHELL.