Achieving corrosion protection in listed antifreeze for fire protection systems

NFPA fire sprinkler standards intended to ensure the safest, most reliable design and installation practices require new antifreeze systems to use a product that is agency-listed and factory-premixed. Existing systems must comply by September 30, 2022. Listed antifreeze products must also prove corrosion resistance to protect against system failure and costly repairs.

The Persistent Problem of Sprinkler Corrosion

The constant presence of water and oxygen in contact with metal pipes and fittings make wet sprinkler systems vulnerable to high levels of corrosion. Galvanic corrosion can also be a problem when the system is comprised of more than one metal. Corrosion not only can render a sprinkler system unable to hold water, but also compromises the system’s designed flow and pressure values. Debris from corrosion builds up, pinhole leaks form, and friction from surface roughness obstructs flow in sprinkler drops and feed mains.

A separate form of piping corrosion, microbiologically influenced corrosion, or MIC, has become another significant challenge encountered in the field. According to FM Global, MIC is responsible for 10-30% of corrosion in all piping systems in the U.S. MIC is the localized and rapid development of metallic corrosion, manifested in the form of pitting, crevices, and craters. This degradation is caused by the growth of certain aerobic and anaerobic bacteria, or hybrids of the two, which tend to form biofilms, and in turn create a sub-environment with different flow characteristics, pH levels and chemical concentrations. Together these conditions can spur MIC and can combine with the more well-known nonbiological corrosion caused by oxygen and acidic exposures. In addition to steel piping, other areas susceptible to MIC include caps, valves, fittings, and supply tanks.

Yet when temperatures fall, antifreeze must prevent damage to equipment to ensure the fire sprinkler system works as planned. In addressing the market need for listed products to protect people and property from the risk of combustion when sprinkler systems activate in a fire, Lubrizol innovated a new antifreeze providing advanced corrosion protection. The product, known commercially as freezemaster™ antifreeze, achieved a UL listing for applications referenced in the current editions of NFPA 13, 13R, 13D and 25 for Residential, Light Hazard, Ordinary Hazard and Storage.

Enhanced Corrosion Testing Protocols

To achieve reduction in corrosion rates, UL 2901, “Standard for Antifreeze Solutions for Use in Fire Sprinkler Systems,” established product testing protocols that must be met or exceeded. Approved premixed antifreeze solutions must not cause the corrosion to exceed 1.0 mils/year (0.025 mm/year) for ASTM A108, Grade 1010 steel; ASTM B16, H02 (Half Hard) brass; or Type 304 stainless steel, among other metallic materials that might be used in sprinkler applications with antifreeze.

Building on more than 30 years in fire protection, Lubrizol formulated a premixed freeze protection technology meeting these baseline corrosion resistance requirements, with cold temperature protection down to -12 degrees Fahrenheit (-24 degrees Celsius), currently the lowest temperature threshold of any listed antifreeze. But Lubrizol went further, bringing the fire protection market an antifreeze that outperforms the other UL-listed alternative in corrosion performance, effectively reducing pipe corrosion by up to 65 percent.

As a performance additives manufacturer, Lubrizol has a core competency and a leadership position in the metal protection industry. That advantage prompted Lubrizol to incorporate several additional metalworking tests and one variation on a third test that UL required into its examination of the best antifreeze formulation for the sprinkler market. The objective: to evaluate whether its new antifreeze solution could prevent corrosive action sooner and better than the alternative listed commercial product.

Corrosion Battle Can Begin Early

Piping on new fire suppression systems may start out with a thin layer of corrosion, and metal fines can be left on the surface from manufacturing and installation. These particles add to the surface area of the system that is capable of corroding and ultimately forming system-clogging sedimentation. Thus the first test method, IP 287 “Determination of Rust Prevention Characteristics of Water Mix Metal Working Fluids,” was intended to evaluate the expected corrosion behaviour of Lubrizol’s new antifreeze on these metal fines, compared to the other UL-listed antifreeze.

In a modified version of the IP 287 test, Lubrizol compared the corrosion behaviour on cast iron chips placed on filter paper and saturated with either its new antifreeze or the other listed antifreeze. After two hours, the chips were removed, and the filter paper rinsed to expose the area covered by the chips and determine a resulting percentage of rust. Lubrizol’s antifreeze presented no corrosion while the other commercially available listed fluid gave rise to 65% rust during the test.

Galvanic Corrosion Safeguards

Fire suppression systems are rarely comprised of only one metal type, or identical grades of a single metal. When dissimilar metals are in direct contact with one another or connected by a conductive fluid, a galvanic cell can form in the sprinkler system where one of the dissimilar metals will corrode preferentially over the other. The second metalworking test derives from ASTM G71 “Standard Guide for Conducting and Evaluating Galvanic Corrosion Tests in Electrolytes.” This test establishes the behaviour of two dissimilar metals in electrical contact in an electrolyte under low-flow conditions. If corrosion is not present, colour changes and sediment in the antifreeze solution will not occur.

Lubrizol built and tested several galvanic cell couples to measure electrical current over time while immersed. UL requires monitoring for 90 days, but in only seven days, it was possible to tell that the voltage versus time curves were radically different between the two solutions, indicating galvanic corrosion occurred more readily in one instance. In addition, the commercial product took on a blue colour during the test, indicating that copper was being leached into the solution. This colour change did not occur with Lubrizol’s new antifreeze, which is listed for use in galvanized piping systems, unlike the other UL-listed product.

A long-term pipe storage test was also conducted to simulate real world fluid-pipe contact. Using Schedule 40 pipe capped with half-hard brass fittings, a sample port was drilled in the top for ease of filling and sampling and sealed with a nylon screw. Samples of Lubrizol’s new antifreeze and the other commercially available antifreeze were added to the pipes and stored at 25 degrees Celsius and 40 degrees Celsius. At the end of 90 days, the pipes were cut open and visually inspected. Corrosion began to appear in the competitive listed solution in that time; Lubrizol’s antifreeze inhibited the formation of corrosion.

Resisting MIC

Finally, in an effort to establish MIC resistance versus the other commercially available listed antifreeze solution, Lubrizol contracted with one of the world’s leading laboratories in analysing metallurgical failure and corrosion behaviour. A screening test was developed to characterize the conditions conducive to MIC. Accelerated testing simulated flow around suspended carbon steel coupons that had been inoculated with sulphate-reducing bacteria (desulfovibrio vulgaris). These microorganisms are common in anaerobic environments where they work to degrade the surfaces they inhabit. After 336 hours of this testing, neither solution showed signs of corrosion, but only Lubrizol’s antifreeze, as determined by DNA testing, lacked any sign of continued biofouling from bacterial growth that could have set up the conditions for a future problem with MIC.

For fire sprinkler systems to do their lifesaving work, they must be protected from damaging corrosion, which can flourish in both wet and dry sprinkler systems because neither are ever 100% dry. In wet systems using listed antifreeze, the chosen formulation has a significant and measurable bearing on just how well corrosion is resisted. Lubrizol, building on its extensive expertise in metallurgy, invested in a series of corrosion tests in addition to those required by UL and was able to demonstrate how much further it was possible to go to resist corrosion of both biological and non-biological origin in sprinkler system antifreeze.

Convert to listed antifreeze before the approaching NFPA deadline

Building owners need assurance that their fire protection systems are reliable and functioning to lower the risk of an uncontrolled fire loss. Fire sprinkler contractors need confidence that the systems they install will not freeze and will provide the best corrosion protection on the market.

September 30, 2022 is the date the conversion to a listed antifreeze must be completed in existing systems, not started. For building owners using antifreeze systems, planning to gear up for the switch well ahead of the next annual inspection, testing and maintenance (ITM) service call is advised. Fire sprinkler contractors can also begin now to actively encourage clients to be proactive on compliance to enhance their life safety practices; a listed product provides peace of mind that the antifreeze meets or exceeds the most rigorous standards. Once implemented, the system need only be tested annually by a qualified inspector to ensure the freeze point is being maintained.

For more information, go to www.freezemaster.com/corrosion