Why Is Steam Condensate Corrosive?

- Apr 17, 2019-

Corrosion will destroy condensate pipes and will generate corrosion products which will negatively affect the operation of the boiler system, especially if part of the condensate is recovered to be used as boiler feedwater.

Why is condensate corrosive?

Make-up water and subsequently boiler feedwater contain alkalinity (here we are referring to low-medium pressure boilers that use softened water).

Alkalinity is the acid neutralizing ability of the water and it mainly consists of carbonate (CO32-) and bicarbonate (HCO3–) ions. Under the influence of heat and pressure in the boiler, the alkalinity ions break down into hydroxyl (OH–) ions and CO2 gas..

2 NaHCO2 à Na2 CO3+CO2+H2O
Na2 CO3+H2O à 2 NaOH + CO2

This free carbon dioxide gas (CO2 ) is volatile and leaves the boiler with the steam and reacts with condensed water to form carbonic acid

CO2 + H2O à H2 CO3

Carbonic acid is a weak acid, but as the condensate water is pure, this weak acid reduces the pH significantly, often in the range of 5-6. At this low pH, the condensate water is very corrosive to carbon steel piping.

You can recognize carbon dioxide corrosion by the thinning of condensate line walls, particularly at the condensate liquid level within the pipe and at pipe threads where the condensate flows.

The cure for this type of corrosion is the neutralization of carbonic acid with volatile amines or ammonia.

You can confirm the above by taking a sample of condensate water and measuring its pH and the concentration of iron in the sample.

Other issues that affect condensate water quality are related to the contamination of the condensate by the process.

How to treat the condensate water?

You can use our alkaline bio ceramic ball, it can make PH of water to be Neutral and alkality, so that the water pipe won't be corrosive

So now it is time to use our alkaline bio ceramic ball