HPAC Magazine

An Ounce Or So Of Prevention

Keep boilers more efficient and corrosion free.

February 1, 2013   By Harvey Grodjesk

Scale and corrosion are major causes of both hot water and steam boiler breakdowns, however the problem is sometimes misdiagnosed and the wrong products and methods are used for repair and prevention. Scale and corrosion not only limit a boiler’s heat transfer and energy efficiency, but they also slowly deteriorate parts and shorten the appliance’s lifecycle.

The number one prevention for this problem is a boiler water treatment. Unfortunately, not every service tech applies an annual boiler treatment, even though most boiler manufacturer’s manuals recommend it. Boiler treatments are important enough to some manufacturers that a bottle is included in every new boiler kit. Other manufacturers require boiler treatments to comply with the product warranty agreement.

SCALE AND CORROSION

The key ingredient to scale is calcium carbonate, which is naturally white in colour.  In boilers however, it turns reddish due to leached out iron oxides that tint the water.  Magnesium, sulfates, magnesium salts and other mineral contaminants can play a role in boiler corrosion, also. 

Water with a high hardness content is typically a scale-forming water. The mineral content of hard water has an inverse solubility in high temperature water. For example, sugar is very soluble in hot tea, but remains a solid in cold tea. Scale acts in reverse. It is more soluble in cold water, which is why inherent scale goes undetected in a cold glass of water. In hot water it is not soluble and it combines with other impurities to create a film of scale.

KEY INGREDIENTS

Since scale and eventual corrosion issues are major boiler problems, a multi-purpose boiler water treatment can prevent scale, or help remove it and corrosion products in systems that have been neglected. Depending upon the inherent local water chemistry conditions, a boiler can seemingly operate fine for five to 10 years without a water treatment, however its longevity may eventually suffer. 

The most effective treatments include a phosphate, which eliminates calcium from forming into calcium carbonate. Instead, when combined with the hardness of calcium the result is soft sludge composed of calcium magnesium phosphate that freely remains dispersed in the water.

An organic polymer is another important ingredient in multi-purpose water treatments, because it prevents the soft sludge from adhering to interior boiler system surfaces. It remains insoluble and free-floating in the system until a blow-down (in steam systems) removes it.

Some boiler treatments incorporate a colour indicator to determine how much to apply and the pH status of the water.  For example, after application, a pinkish purple water sample may indicate a proper pH water chemistry of approximately 8.2 to 9.0, which is neither too alkaline or acidic, while blue or bluish green water indicates more water treatment is needed. A complete flushing may be needed if subsequent applications do not generate the proper water colour.

In the case of boiler treatments without a reactive colour, the colour of the treatment indicates it has been applied and does not indicate any pH changes or proper water chemistry. This is similar to automotive antifreeze. A greenish water colour in an automotive radiator proves antifreeze is present, but gives no indication of how much or what temperature protection it provides.

CUT THE FAT

What should not be included in a boiler treatment is any kind of petroleum distillates, which have fatty acids. When combined with the inherent alkalinity of boiler water, fatty acids can create soap and surging.

Petroleum distillates also attack rubber boiler parts, such as gaskets or push nipples.

Most treatments are formulated for hot water as well as steam systems and serve multiple purposes such as:

• removing sludge and rust scale;

• inhibiting boiler and steam line corrosion;

• preventing oxygen pitting;

• inhibiting lime scale;

• preventing surging and foaming; and

• performing water chemistry checks;

Too much alkalinity can cause surging, scale build-up, or eventually caustic “embrittlement,” a process that causes metal cracking. Too much acidity, on the other hand, leads to corrosion. In large commercial boilers, these ailments are averted with daily checks typically performed by maintenance staffs trained to use sophisticated test kits to determine the boiler water’s total alkalinity, water hardness, total dissolved solids and other common water chemistry conditions. Conversely, the average residential boiler service technician may not have this training or available jobsite time to execute such tests. Therefore, a boiler water treatment that reacts to operating conditions for proper water diagnostics is critical.

Water treatments that minimize corrosion are more important today because boiler walls are manufactured thinner for increased heat transfer, and the recent influx of overseas metal alloys are not always reliable. Corrosion and scale can also create hot spots, percolating noise and active pitting sites that could affect the system’s future integrity. Another diagnostic sign is water discoloration, which in hot water boilers probably signifies built-up layers of corrosion.

Most of the aforementioned prevention methods are not a matter of life and death, but heating systems left untreated may fail prematurely or need repairs that could be easily avoided with annual treatments and check-ups. Therefore it is the service technician’s responsibility to use preventive products. The bottom line behind all heatingproduct additives is to keep the customer’s equipment efficient and problem free.

Harvey Grodjesk, who is vice president–operations for the Stewart-Hall product line of Rectorseal Corp. (www.rectorseal.com), is a 37-year veteran of the heating chemical product industry.

SIDEBARS: 

Profit Makers

The checklist of proper boiler operating functions, such as drawing flue gasses, proper water levels, ignition efficiency, etc., should always include examination for scale and voluntarily adding a boiler treatment as a preventative. Industry studies prove most homeowners will gladly pay for products that extend their equipment’s lifecycle. It is also an extra profit margin for the service company. Boiler treatments might sell for less than $15 wholesale, but can easily be charged up to $45 on invoices because it has to be applied and then followed up with pH checks and other post-application factors.

Steam Boiler Surging

One of the most frequently occurring steam boiler problems is surging or water hammering, which generates noise and vibrations, the latter which can eventually damage pipes. Besides annoying sounds, another problem is short on/off cycling caused by water surging up the pipes and triggering a low-water alert that shuts down the boiler prematurely or operates sporadically until the surged water returns.

Pure H2O will not surge, but surface contaminants will surge similar to boiling water when noodles are added. The inherent process of steam is water evaporating inside the system, which leaves behind the scale and other heavy mineral element. Oil, which can occur from pipe thread sealants or pipe cutting processes in new installations or repairs, can also add to the surface contaminants. Fluxes are fat-based and they too can congregate at the surface.

These contaminants alter a boiler water’s pH, which ideally should be operating between 8.5 and 9.0. Beyond this ideal pH range, a boiler has the potential for surging. Surging can be cured with an additive, however oil-based contaminants in stea
m boilers require a different chemical treatment versus scale contaminants in surging systems.

Another type of surging is caused by total dissolved solids (TDS), which occurs when the water becomes too concentrated during the heating process.

A blow-down of the boiler eliminates TDS, but few homeowners are capable of boiler blow-downs. Instead, the responsibility of the conscientious service tech to blow-down the boiler on every service call. If TDS become too high, surging and significant mineral build-up can occur.

Unlike the universal use of general boiler treatments, anti-surging additives should typically be applied after a problem occurs. However, an anti-surging additive might be considered as a preventive if a boiler has a history of reoccurring surging.

Sealers

Since boiler walls are thinner today, hairline cracks in the boiler shell or pinhole leaks in the tubes of steam boilers are more common. Push nipples tend to leak due to expansion and contraction of the metal surfaces. 

Consequently, boiler sealers have become a standard stocking item for the heating service truck. Boiler sealers are applied to the water and settle into crevices and voids to stop leaks. Once again, its scale and corrosion that typically cause this damage, therefore proper boiler water management can prevent cracking and pitting.

Sealers typically come in quart or gallon containers. The base is an organic polymer that’s insoluble with water. The sealer is applied to the water and works from the inside to out. Eventually the polymer works its way into a crack or pinhole and dries into a bond as it migrates to the exterior of the boiler. Depending on the size of the crack, the sealing process could take up to one week before results occur. Sealers will not work on cracks that are too large. 

Sealer dosages are typically one quart every 15 gallons of boiler water. Over dosing can create surging in steam systems or lock up a pump in a hot water system.

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