Boiler Scale: The Silent Killer

A wise man once said, “Boilers are only as good as their feedwater.” Quality feedwater ensures  the internal components of a boiler are able to function properly and efficiently. However, when there are impurities present in the feed water, problems quickly arise. Poor feedwater treatment leads directly to boiler scale. 

Tube CleaningBoiler scale is a buildup of matter, chemicals, or minerals that harden inside of the boiler.  As the boiler created stream,  the impurities commonly solidify along the tube surfaces, creating scale. This drastically drops the boilers ability to transfer heat which decreases effiecnecy and can lead to a number of other problems.

Boiler Scale Variations


These deposits are mostly granular and extremely porous. They are characterized by large crystals and very dense, uniform patterns. Another way that these deposits can be identified is if bubbles of carbon dioxide appear when an acid is dropped into it during testing.


Characterized by smaller crystals, sulfate deposits are the second variation of boiler scale. This type of deposit is extremely dense as well as being sturdier than the carbonate deposits.  While the deposit is brittle, it is very difficult to pulverize. Lastly, when dropped in acid, sulfate deposits do not bubble.

High Silica

The composition of high silica deposits is very similar to that of porcelain. The silica crystals are very small and form an impassable scale. Much like the scale of sulfate deposits, it is brittle, very difficult to pulverize. When it comes into contact with an acid, it does not effervesce.

Iron Composites

Iron composites come from contamination by iron or corrosion in the feed water of the boiler. A dark colored scale is a good indicator that iron composites are present as well as a magnetic charge. The solubility of the composite is extremely high, and when dropped in acid, it produces a dark brown solution.

How Is Boiler Scale Going To Affect Your Boiler?

Fuel Differential

A boiler with no scale might require one unit of dry fuel to convert 10,000 pounds of water into steam. But, the presence of scale will increase the amount of fuel needed in order to produce the same amount of steam. Not only does this cause your facility to use more fuel, but it also shortens the life span of your boiler. If your boiler is running constantly with this fuel differential, it is working in overdrive for extended periods of time. The result of this is an increase in boiler malfunctions, heating inefficiencies, and a spike in maintenance costs.

Efficiency CostsBoiler Repair

As stated above, poor boiler efficiency can lead to many downsides. The numbers paint this picture extremely well. In a 250 hp, a 1,000 hp, and a 1/16″ boiler, a 1/64″ scale deposit can cost around $10,000, $45,500, and $69,000, respectively.

A 1/32″ scale deposit can cost $20,000, $81,000, or $140,000.

And a large deposit, 1/16″, can run up to $42,000, $168,000, and $293,000. To facility managers, these numbers are a warning sign of the financial effects that scale can have on their boilers.

Maintenance Expenses

When working with any large piece of machinery, maintenance expenses can stack up quickly. Crack tube repair or replacement can range from around $500 to $1,800 depending on the boiler size. Sometimes repairs can take a few days or even up to a week to complete, which sets the business back in a big way.

How can you avoid scale?

Feedwater management

Rakhoh gives a great explanation of the basis of feedwater management.

“The most significant factor of causing scale in the boiler is the low quality of feedwater. Boiler manufacturers suggest pretreatment of feedwater that involves analyzing the water source and its quality. Also, the removal of suspended or dissolved solids through the process of filtration, softening, or demineralization”

feedwater damage inside a boiler

Regular Maintenance

One of the best ways to stay on top of your boiler’s health is to schedule regular maintenance checks. Having professionals inspect your unit ensures that efficiency, safety, and quality are held in the highest regard. The life span of a boiler is extended drastically when buildups are caught and resolved early.

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