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Formation and Removal of an Iridescent Discoloration in Cleaned-in-place Pipelines

Department of Microbiology and Public Health, Michigan State University, East Lansing

P. H. Tracy

Department of Food Technology, University of Illinois, Urbana

ABSTRACT

In the course of some studies on in-place cleaning, Kaufmann et al. (2) reported the appearance of an iridescent discoloration on the interior of 18-8 stainless steel pipes after cleaning with an alkaline cleaning compound containing a nonionic wetting agent. Since this type of film has not been reported previously in the literature, this work was undertaken to determine some conditions of operation which would (a) cause the discoloration and (b) remove the discoloration.

Film build-up. The permanent CIP line used in this study consisted essentially of four sections of stainless steel pipe, each about 10 ft. long. Two sections were 500-grit finish, one was 300, and one was 180-grit finish. During the period of film deposition, the line was used for hot milk.

Immediately after use, the line was flushed with tap water at 90° P. and washed, using nonionic alkaline detergent "D" at the minimum recommended level. After flushing with tap water at 90° F. to remove the detergent solution, the line was chlorinated for 1-min., using 200 p.p.m. of chlorine.