How boilers are effected by corrosion ?

What is boiler corrosion? How did a boiler get corroded?

The process of decaying or disintegration of boiler material either by a chemical or electrochemical reactions with its environment is known as boiler corrosion 

Causes of boiler corrosion :- 

The causes of boiler corrosions are as follows

1. Due to the presence of dissolved oxygen :- 

As we know that the water which is feed to the boiler contains some amount of oxygen as well as usually it contains about 8ppm of dissolved oxygen at the room temperature 

When the water inside the boiler is heated then dissolved oxygen in the boiler feed water is also get heated due to the heating of dissolved oxygen of water it evolves some gases which becomes the reason of corrosion inside the boiler 

2. Due to the presence of carbon dioxide :- 

As we know that the natural water also contains some amount of carbon dioxide in it but also it may be released inside the boiler during the process of generation of steam.

3. Due to the presence of acid forming salts :- 

The inner walls of boiler may also be corrode due to the presence of some acid forming salts inside the boiler which comes along with the boiler feed water 

Water which is used for the boilers contains chlorides of magnesium and calcium in it which hydrolysed to form acids and which has corrosive action on the boiler material 

Where as magnesium chloride present in boiler feed water hydrolysis completely at 200`C to form hydrochloric acid 

At last the liberated acids react with the boiler material (which is iron) in a chain like reaction producing hydrochloric acid repetitively which causes extensive corrosion. 

Here calcium chloride also goes hydrolysis but to a lesser extent.

It hydrolyse to an extent of 25% at 600`C silicic acid catalyses the reaction therefore if water contains contains silica than an appreciable quantities of HCL may be formed even at the lower temperature 

And this type of corrosion in the boiler could be prevented by adding alkali to neutralize the acid which is formed inside the boiler 

4. Formation of galvanic cells :- 

The boiler may also corrode due to the formation of galvanic cells between the iron and other metal present in the alloy used in boiling fitting; this may also lead to boiling pitting corrosion. 

This type of corrosion can be prevented by suspending zinc plates which act as a sacrificial anode inside the boiler 

I hope the above mentioned information helped you to understand about the causes of corrosion occurring inside the boiler. 

thankyou 

BY :- ADARSH GUPTA