Corrosion: how to control it?

Abstract

Established in 1989, Oslo Heart Centre (OHC) is located in downtown Oslo, Norway. The hospital is a non-profit cardiac surgical clinic. To control the temperature in the hospital during the summer months, an air-conditioning system is installed. The ten years old air-conditioning system suffers from corrosion problems, inside and outside stainless steel pipes. The aim of this project is to find solutions in order to reduce the amount of corrosion. Heat loss due to an insufficient insulation, contamination and erosion are secondary, indirect problems. To analyze the situation, various measurements were performed such as, pipe thickness (amount of corrosion), humidity and water quality. It appeared that: · The pipes thickness is decreased with 0,7 mm due to corrosion. · The humidity is 100%, for both inside and around the insulation. · The pH value (pH = 8) and the amount of iron parts (0,15 mg/kg) are not within the boundaries of the recommended values. Moreover the measured O2 level is misleading. After an inspection concerning the existing conditions, the problems were defined and organized by priority. The main problem is corrosion which occurs due to three sub-problems: · A too high O2 level in the water-glycol mix, which provokes rust by a chemical reaction. · Uninhibited glycol which turns sour in acids by reacting with the metal pipes. · Insufficient insulation which provokes water vapour condensation at the pipes surface. To control these problems, the following solutions have been suggested: · Reduce the O2 level. · Remove the glycol and replace it with a product which contains inhibiters against corrosion. · Change the old insulation and replace it with a more water vapour resistant insulation. After several comparisons of different techniques, products, environmental consequences and an economic analysis based on a ten years period, solutions for each problem are suggested: · Add H2 to the water-glycol mix to form a chemical reaction with O2. A system provided by the Norwegian company Niprox® (costs: less than 2000 €/year). · Replace the glycol with an inhibited propylene glycol (costs: less than 10000 €/year). · Use Armaflex® foam sheets as insulation outside the pipes, for a better resistance against water vapour. (cost: about 5000 €/year) With all these alternatives, the OHC could reduce the amount of corrosion within the air-conditioning system.