Physical factors influencing bacterial fouling of type 304 and 316 stainless steels

The influence of biofouling of physical and chemical surface features is not well known. This paper compares the surfaces of specimens of type 304 and 316 stainless steels. Gross surface roughness (Ra) values revealed no differences between specimens of the two steels for nominally similar grades of surface finish. However, atomic force microscopy revealed a significant difference in surface roughness on a more microscopic scale, with the type 316 stainless steel specimen being smoother than the type 304 material which had significantly more microscopic surface scratches, grooves and associated deformation. Chemical analysis showed that the only major difference in the compositions of the passive surface layers on the two steels was the presence of molybdenum for the type 316 steel. Results are presented on the development of potable water biofilms over 12 months in stainless steel pipes appended to the plumbing distribution system of a large building. The viable cell counts on a type 304 stainless steel pipe after 12 months averaged 2·8 × 10³ cfu cm⁻² (cfu = colony forming units) as opposed to 3·6 × 10² cfu cm⁻² on a type 316 pipe.