MIC in the Fire Water Sprinkler System at St. Olavs Hospital, Trondheim, Norway

Abstract

Corrosion-related leaks and blockage of steel pipes are one of the main problems for operation and maintenance of water-based fire protection systems (FPS). Repair of corrosion damage due to mechanical failure significantly increases the life cycle cost of a fire sprinkler system. The fire protection system at St. Olavs Hospital in Trondheim consists predominantly of carbon steel piping, although some parts have been replaced by AISI 304/AISI 316 stainless steel pipes. The system is fed with untreated drinking water taken from the municipal drinking water supply in Trondheim, and the water is stagnant in the system until a fire occurs. During an inspection in the fall of 2017, severe corrosion attacks were discovered inside the pipes. Large amounts of corrosion product and tubercles on the inner pipe surface suggested corrosion caused by bacterial activity (MIC – Microbiologically Influenced Corrosion). The determination of MIC proceeded through analyses of the bacterial content and chemical parameters of the water. Water was taken from the fire system, which had been stagnant for a period of five years, and from the municipal drinking water supply in Trondheim. Microbial Community Analysis (MCA) was conducted on the corrosion products to determine the total number (abundance) of bacteria and different types (diversity) of bacteria present in the sprinkler system. Based on the results from the chemical and microbiological analyses, as well as metallurgical evidence, MIC was determined to be the main cause of the corrosion problems in the FPS. Localized corrosion attacks in the form of pits were documented, together with a high number of MIC-related bacteria.