Scale Build-Up in Industrial Steam Boilers – What It Is and How to Prevent It

Left unchecked, scale build-up in an industrial steam boiler can negatively impact your boiler’s efficiency and lead to damage to the boiler tubes inside your boiler’s pressure vessel. This blog looks in more detail at what boiler scale is, the impact it can have on your steam boiler system, and what you can do to mitigate the risk of steam boiler failure.

What is boiler scale?

Boiler scale is the build up of dissolved solids left behind once water has been converted to steam in the gas phase. Calcium carbonate (CaCO3) and magnesium carbonate (MgCO3) are two very common and natural chemical compounds found in water. When we refer to ‘water hardness’ in the steam boiler industry, we mean the presence of these compounds in the feedwater supply we use for generating steam.

The problem with untreated (or hard) water is that it can lead to scale build-up. Dishwashers, laundry machines, and even your shower heads can get a build-up of this scale. It looks like a powdery white residue and is left behind once these minerals have been precipitated out of heated water.

If you think of a steam boiler’s pressure vessel as a heart, the scale build-up is the fats, cholesterol, and other substances that can clog your arteries. Once the arteries become clogged, the heart has to increase pressure and work even harder to transfer the blood through smaller channels. This increased pressure can cause serious damage to both the heart and arteries, risking a rupture. Below are pictures of scale build-up within boiler tubes that can seriously affect pressure and heat transfer.

What problems can scale build-up cause?

Water hardness and resultant scale are a significant risk for any water heating system, including an industrial steam boiler. Let’s look at a few more severe headaches that scale build-up can cause.

Scale build-up in steam boiler tubes acts as an insulator

Steam boilers rely on heat transfer from the fireside, through the metal tubes to heat the water to generate steam. Scale, however, is a poor transfer of heat and acts as an insulator on the boiler’s metal pipes; this means that a scale layer prevents heat from easily passing through the tube to heat the water, impacting required energy inputs and steam outputs.

The ramifications of scale build-up are significant.

• Poor heat transfer leads to decreased efficiency, as more gas fuel or electricity is needed to generate heat to produce the required amounts of steam. A layer of scale just an eighth of an inch in thickness can cause as much as 20%-25% in efficiency loss.
• Scale build-up puts more heat stress on the metal itself, causing damage. The boiler tubes begin to absorb more of the heat instead of passing it through. This increase in a boiler tube’s temperature can cause it to reach its melting point, causing it to warp, bulge, and expand. At this point, you run a very high risk of a ruptured tube, which can cause severe ramifications.
• Boiler failure will ultimately lead to unscheduled downtime, which has serious financial and production implications on any company dependent on steam for its daily operations and outputs.

How to treat water hardness and prevent scale

The issue of hard water and scale build-up is not a new one, and steam boiler manufacturers like Miura have been developing and perfecting ways to treat boiler feedwater for decades now. These innovations include a range of water treatments and sophisticated monitoring systems that alert steam boiler operators and integrated boiler operations to water hardness before scale build-up can even become an issue.

Let’s take a look at some of the top prevention measures that Miura, specifically, offers.

Dual-tank water softeners and salt bath regeneration

Treating hard water is one of the primary ways of preventing boiler scale. Miura’s MW dual-tank water softeners are vital components of any Miura modular steam boiler system. These water softeners look like large gas canisters but are filled with resin beads that capture dissolved solids, including CaCO3 and MgCO3, inside the canisters, preventing these compounds and minerals from entering the steam boiler feedwater system.

Miura’s dual tank water softener design allows for the simultaneous regeneration and operation of the softeners so that there is a continuous and uninterrupted production of soft water for the steam boiler system.

Chemical treatments

To help protect your boiler from scale build-up, you can also utilize specially designed boiler water chemicals. Miura has developed its brand of water treatment chemicals, BOILERMATE®, for its once-through, on-demand, modular steam boilers.

• BOILERMATE® 1200S is Miura’s all-in-one boiler water treatment. It’s a silica-based product that creates a protective layer of film on the water tube surface to protect against corrosion. It also includes a small dosage of scale dispersant that safeguards against the minute amount of hardness that conventionally leaks out of a water softener. BM1200S effectively treats hardness if used in a system with an active and effective water softener – i.e., BM1200S is not intended to handle large concentrations of hardness.
• BOILERMATE® BM2100D is a scale remover and iron dispersant. If your boiler suffers from scale build-up, this product uses an acid-base chemical to eat away scale from the boiler tubes and flush them out of the system.

​Hardness Detection

Routine testing for water hardness is essential for hardness damage in a steam boiler system. While it’s the responsibility of the boiler operator or owner to test periodically for water hardness, Miura’s Colormetry Hardness Detection System also assists with detecting and alerting operators to hardness leakages. The colormetry unit has been designed to sample and test pre-treated soft water at regular intervals. It can communicate results with other Miura components and notify the operators via its display that the action is required to prevent potential hard water damage to the steam boiler.

Control and monitoring

Miura’s BOILERMATE® Chemical Monitoring System works together with the BL Micro Controller and Miura Online Maintenance (MOM) to regulate the amounts of chemicals being administered to help prevent the overuse of the products.

Each Miura boiler also comes fitted with a BL Micro Controller, a boiler control interface that allows operators to navigate the boiler control panel and, among other things, monitor the surface temperature of the water inside the boiler tubes for early scale build-up detection. Rising temperatures signal that scale formation in the boiler tubes needs the operator’s attention.

Scale formation in a steam boiler is both common and preventable. With the proper controls and measures in place, you can protect the inside of your pressure vessel, prevent any unnecessary and costly downtimes, maintain operational efficiency, and ensure the ongoing safety of your boiler room.

Contact a Miura representative to discuss your industrial steam boiler needs today or to ask any questions you may have about our water treatment systems and products.