The influence of welding procedures on bacterial colonization of stainless steel weldments

The US food processing industry requires that food contact stainless steel surfaces have a No. 4 surface finish, with welds having a surface finish equivalent to the parent plate. To meet this standard, most welds must be ground and polished, which significantly increases the cost of fabrication. Two laboratories have independently compared colonization of seven plasma arc welds, not subjected to grinding and polishing by either the human pathogen Listeria monocytogenes, or a 3-member bacterial consortium containing Flavobacterium spp. that were isolated from weldments in a seafood processing plant. Bacteria did not appear to preferentially colonize the surface of welds over that of adjacent parent 304L stainless steel with a 2B finish (equivalent to No. 4). The results suggest that the current practice of grinding and polishing welds to achieve a No. 4 surface finish that meets current food industry roughness standards may have no significant influence on short-term bacterial accumulation.