Boiler corrosion is a relevant problem that is majorly caused by the presence of oxygen and carbon dioxide dissolved in the feed water, and also due to low PH level of water. Boiler corrosion is an electro-chemical reaction and usually causes pinpoint pitting on a sound boiler metal. Most of the other surface of boiler metal can be sound and still a single penetration, caused by corrosion, can result in boiler failure of operation.
Feed water, if left untreated, tends to be highly corrosive to the metal due to dissolved oxygen in it. However, mere treatment of water id not enough. Although treatment of feed water before employing it can decrease the level of oxygen dissolved in it and de-aerators also help as well, still sufficient chemical reserves of oxygen-scavengers must be essentially maintained so that boiler metal can be prevented from corroding and hence save cost and time of repair.
Boiler corrosion can prove to be bad for the boiler and subsequently for the manufacturing unit or any unit that it is employed in. Boiler corrosion can result in time lost due to work being down and also cost of replacement or repairs. It can also pose safety concerns. Therefore, proper maintenance to prevent such issue and monitoring of boilers with plc based boiler control system is essential.
Here are few measures provided by Industrial Boiler Manufacturers in India that can be followed to prevent boiler corrosion.
1. Brand new boilers must be boiled out with alkaline cleaners after new tubes are installed as these tubes usually come with oil layer on the surface or other coating. These coating generally serve the purpose of preventing rust but if not removed can cause metal to corrode.
2. Recommended quantities of sodium nitrite or sodium chromatic must be added to the water as they act as nitrate inhibitors.
3. In case the boiler is used in damp locations or in greenhouses, make sure to place trap with unslaked lime in the ash pit and close the lid of the boiler. This will help in absorption of moisture in the boiler, if any. The Lime must be replace if it turns mushy.
4. As soon as the boiler is water-filled, bring it to the temperature of 180 degree Fahrenheit to deaerate the water. It may not eliminate all the air but it will remove most of it.
5. Various fittings of the boiler as well as the system must be kept airtight.
6. Low sulphur content fuel must be used, preferably, so as to prevent sulphur gas from causing corrosion.
7. In order to remove oxygen dissolved in feedwater, sodium sulphite can be regularly used.
8. Feed water must be suitably pre-heated and deaerated to eliminate oxygen dissolved in the water.
9. Prevention of water leakage is a must to avoid corrosion. Also drainage of water from the system must be avoided as it gives space for the water to be introduced in the system which can further cause corrosion.
10. The inner surface of the boiler fire-tubes must be properly cleaned to remove any residue that may lead to corrosion.