Corrosion in boilers can almost always be traced to one or both of two problems. The most common cause is dissolved oxygen entering the system via the feed-water. The oxygen causes localized corrosion to occur in the form of pitting. The pits are small but they are deep pinpoint holes which eventually can penetrate tube walls and cause their failure. Another common cause of corrosion in boiler systems is low PH within the boiler. This reduced PH may result from carbon dioxide infiltration or from contamination by other chemicals. Oxygen corrosion is normally controlled by driving the oxygen from the feed-water in a deaerating heater or by chemically removing it with an oxygen scavenger such as sodium sulfite. There are many contaminates which can infiltrate a boiler system and cause low PH levels to develop. Manufacturing wastes such as sugar or acids from plating operations which can be returned to the boiler with condensate can be a source of problems because they concentrate in the boiler. Oxygen can infiltrate the boiler system at virtually any point. When dissolved, oxygen that is present in boiler feed water can attach on feed lines, pumps, and economizers. The severity of the attachment depends upon the concentration of the oxygen and the temperature of the water.