Overcoming Challenges in Corrosion Protection for Heating Systems

Corrosion within a heating system often determines its useful lifespan, as different metals are susceptible to corrosion in various ways. It's crucial to take proactive measures to protect central heating system metals against corrosion due to its significant impact.

Natural corrosion is inevitable in central heating systems, and the repercussions of boiler and radiator failures are both disruptive and costly for homeowners, presenting major challenges for installers. Therefore, understanding the causes and effects of corrosion on different system metals is crucial. Understanding and preventing corrosion in a central heating system will ensure that the system is operating at its most efficient and will prevent serious damage to the equipment in the system or the property itself, arising from leaks.

Corrosion in a central heating system begins from the time of installation and commissioning. Water in the system reacts with the steel in the radiators, leading to corrosion. To mitigate corrosion rates, plumbers typically flush out newly installed systems to eliminate debris or substances that could accelerate corrosion or pose a risk.

Challenges

While there are numerous challenges in the industry for preventing corrosion in heating systems, perhaps the three main challenges are: 

(1) Knowing the metals used and any new design features in the heating system,

(2) Understanding the operation cycle of a heating system

(3) Having a properly designed preservation plan in place for when a heating system is to be out of service for extended periods of time. 

Newer heating systems are typically designed with more heat transfer efficient solutions which, as a consequence, can lead to a higher potential of corrosion if not properly addressed. Corrosion protection is a key element to the sustainability and reliability of all the components in a heating system and is especially true for the high value assets. Corrosion protection is also critical in reducing liability resulting from a system that fails. A failed system could result in unplanned, and unbudgeted, equipment replacement, uncontrolled leaks in sensitive areas of a facility, and loss of services that the heating system provides. Having to resort to temporary equipment (boilers, chillers, etc.) will also drive up the operating budget for a facility.

Operational Requirements

The trend in recent years has been to "fill in the gaps" of protection that exist when using traditional chemical solutions for corrosion protection. Understanding the operational requirements of a system very important. If a system is in operation 24/7/365 there is less potential for corrosion in a system. However, a system that is shut down days/weeks, months at a time, or even a system that has multiple circulation pumps (for redundancy) there is a period of time of no flow (static) for some, or all, of the system, that creates a gap of protection.

For example, by the nature of how a traditional chemical program works, it does not provide protection for a system that is not in service. Corrosion inhibitors have shown to be effective not only in operating systems, but they continue to provide protection in "this gap" when a system is partially or fully static. Even more important is that the vapor-phase corrosion inhibitor component, protects in any area that the water level has dropped, and an air space exists in the system.

For systems that will be shutdown for longer periods of time (+30 day, months, years) there are products available that support seasonal shutdown as well as mothballing of systems. Each product offers protection that will allow for less corrosion-related startup issues when the system is placed by into service. Best Practices should be evaluated for the entire system and its individual components as well as the operating cycles for each system. A single facility could easily have multiple systems that each have different conditions that need to be evaluated. A properly developed treatment and preservation plan will have identified "the gaps" of protection that need to be addressed.

Metal Selection

It is recommended for companies in product development to focuse on the changes in metal selection in a system has seen the increased use of aluminum which can lead to significant issues if the current chemical treatment program is evaluated and not modified if required. Traditional chemical treatment programs include maintaining a high pH (>9.5) as that tends to help with microbial control and less corrosion potential. However, aluminum's amphoteric properties mean a system operating at an elevated pH will result in an accelerated loss of aluminum. It is desirable that technology works in a pH range that supports the use of aluminum in boilers and other heat exchangers.

Regulations

Changes to corrosion control products in the industry can happen as a result of the three challenges listed above  but can also be driven by changes in environmental regulations at the local level and national levels. For example, The Enviromental Protection agency (EPA) issued a final ruling in 1994 that prohibited the use of hexavalent chromium for use in cooling towers. More recently, other conventional corrosion inhibitor chemicals are facing more restriction that require an alternative to ensuring the heating systems are protected.

Understanding a facility's heating systems and the type of protection needed is very important before recommending a solution. It is the discussion of that system with the customer that will bring out the product of choice.

Ana Juraga, Content Writer at Cortec Corporation, has been with the company for 14 years. Besides dealing with media relations she collaborates with Cortec’s engineers and chemists in creating informative technical content.

Scott Bryan, Product Manager – Water Treatment and Coating Additives, Cortec Corporation,  is a graduate of the United States Naval Academy and has retired after 29 years of combined Active and Reserve duty. He has 25+ years in the Industrial Water Treatment Industry and has maintained the CWT (Certified Water Technologists) certification since 2005.