Abstract
Biofilms develop on metallic surfaces in contact with natural waters. Biofilms can contain microorganisms which accelerate corrosion. The chemical composition and microstructure of weldments, as produced by welding processes and heat treatment, can influence the degree of accelerated corrosion. It may be possible to avoid costly pitting failures if the weldment could be less susceptible to microbiologically influenced corrosion (MIC) by proper selection of filler metal, welding process variables, or heat treatment.
Field testing and subsequent laboratory electrochemical analyses were conducted to examine the role of welding and heat treatment variables on MIC of austenitic stainless steel weldments. Pipe specimens were fabricated (GTAW) of both 304L and 316L for field testing. Filler metals were selected to produce three percentages of ferrite content (low, medium, and high). Weldments of each ferrite content were evaluated in both as- deposited and solution-annealed conditions. Field testing involved exposure of the weld specimens for approximately one year to a small trickle of water directly from a well known to produce MIC. Mounds indicating biomass formation appeared on the welds after two weeks, exposure.
Laboratory electrochemical analyses involved measurements of corrosion potentials as a function of time and critical pitting potentials for weld and base metal samples in microbial solutions.
