L.H. Boulton, Nickel Institute Consultant, New Zealand
It has been observed over years that an unusual surface morphology appears on stainless steel surfaces at circumferential welds in vessels (commonly austenitic grades 304 or 316) if microbiologically influenced corrosion (MIC) occurs due to contaminated water lying stagnant in the vessel for a period of time. The unusual appearance of the MIC pattern has been described as tiger striping. There does not appear to be any satisfactory explanation in the literature as to why the tiger stripe phenomenon occurs.