Comparison of surface sampling methods and cleanability assessment of stainless steel surfaces subjected or not to shot peening

The cleanability of AISI 304 stainless steel surfaces, indicated by the removal of Escherichia coli cells or Aspergillus niger spores was assessed by controlled inoculation and washing treatment of samples in standardised conditions. Two systems of recapture (Rodac plate technique and swabbing technique) were compared. Four industrial finishes, subjected or not to shot peening, contaminated at low concentration (1-10 cfu/cm(2)), and then washed with distilled water or alkaline detergent, were examined. The Rodac plate technique detected most of microorganisms inoculated (80% for E coli cells and 67% for A. niger spores), whereas the swabbing technique recovered only 1% of the K coli cells and 26% of the A. niger spores. Using the Rodac plate technique E coli cells proved to be easily detachable from samples either with distilled water (98%) or alkaline detergent (>99%). For the surfaces contaminated with A. niger spores, the cleanability increased from 34% with distilled water to 77% with alkaline detergent. In these working conditions type of finish (shot treated or not) had no significant effect on cleanability of stainless steel.