Equipment redundancy, supported by impactful corrosion protection, can create a potent combination for avoiding unplanned downtime
In the chemical process industries (CPI), production would come to a standstill without process heating and cooling systems. There would be no cracking and distillation at petroleum refineries. Power plants could not produce steam to rotate turbines and generate electricity. Unfortunately, the CPI experience this lost productivity when planned or unplanned maintenance takes boilers, heat exchangers and cooling-water systems offline. That is why corrosion prevention and redundancy for critical assets are such important ingredients in the standard maintenance recipe. By making these principles part of routine operations, chemical and energy facilities can pursue mission readiness and peak performance for maximum profitability.
The high stakes of downtime
The cost of downtime all depends on the value of what could have been produced under normal operating conditions. A simple way to estimate this is to calculate how much value could have been created during a standard hour of uptime (for instance, the value of crude oil refined or power produced during a normal hour of operation) and multiply that by the number of hours that production was suspended. In the energy sector, the losses can be astronomical. For example, Siemens reported that one hour of downtime in the oil-and-gas industry was as low as $200,000 in fiscal year 2019 and as high as $600,000 in fiscal year 2022, mirroring the swings in the cost of a barrel of crude oil [1]. At a facility operated continuously around the clock, that adds up to a potential loss of $14 million per day. In the world of power generation, it has been suggested that one hour of downtime costs $300,000 [2], which adds up to $7.2 million in 24 hours. CPI facilities that temporarily lose the steam needed to drive operations will lose the value of whatever product that steam could have helped manufacture during that downtime. Lost productivity could go on for a few hours, a few days or a few weeks depending on how long it takes to repair or replace the assets in the event of damage or failure (Figure 1).
FIGURE 1. Corrosion in a firetube boiler led to replacement of one of the tubes. Any procedure like this necessarily increases downtime and can prove quite costly
Redundancy for reliability
One way to deal with the risk of potential downtime is to employ backup systems that can take up the slack for lost heat, steam or cooling water. This is especially important for power generation, which must always ensure mission readiness and reliability for its customers. Refineries also have little margin for error due to the high value of the “liquid gold” they process. In short, the more critical or valuable the process is, the more important it is to have redundancy. If one boiler fails or needs to be pulled offline for maintenance, a backup boiler can be started almost immediately to minimize downtime and loss of production. However, if workers encounter corrosion problems when they start up these backup boiler and cooling systems, the plant is back at square one with no redundancy.
Reliable corrosion protection
Corrosion not only threatens reliability for backup systems, but also for those in operation. Although too often overlooked or pushed out of mind until it becomes a problem, corrosion causes serious issues, such as clogging, reduced water flow and reduced heat-transfer efficiency. If corrosion proceeds for long enough, it thins the walls of the system, shortening equipment service life and leading to debilitating leaks and labor-intensive repairs (Figure 2). High iron levels can also “poison” the chemistry of the existing water-treatment program, causing a chemical reaction that reduces the treatment’s effectiveness. It is therefore important to implement corrosion protection into the maintenance routine at all stages of the heating and cooling systems’ lifecycles. This will help maintenance teams avoid unnecessary problems and achieve maximum uptime during operation, scheduled maintenance and unplanned maintenance.
FIGURE 2. Corroded boiler tubes (brown) versus new boiler tubes (shiny) show the toll corrosion can take on asset integrity and longevity
Maintenance must-haves
Incorporating corrosion inhibitor technologies into the normal water-treatment plan for boiler or cooling water systems is a standard industry practice — but it should not be taken for granted. Sometimes, maintenance teams may overlook this basic step simply because they are uninformed. This was the case for one plastics manufacturer that suddenly faced unexpected downtime from severe corrosion inside a cooling-system vacuum pump. A lack of pressure led them to this discovery, and the associated production line came to a standstill for several weeks until the replacement part arrived and the pump could be fixed. This experience alerted the manufacturer to the fact that their maintenance team was not using a corrosion inhibitor in their cooling-water system (Figure 3). They subsequently began doing so, implementing a simple fix that only needed more awareness on the part of their maintenance team [3].
FIGURE 3. Without a corrosion inhibitor in the cooling loop, the pump could experience corrosion, interrupting normal operations
While a basic corrosion inhibitor is essential, there are many different technologies available with a wide range of capabilities for different process needs. Many corrosion inhibitors offer contact-only protection, meaning that they only protect metal surfaces in direct contact with the water to which they are added, leaving surfaces in void spaces above the water more vulnerable to corrosion attack. A vapor corrosion inhibitor (VCI) dissolves in water to protect submerged surfaces and vaporizes out of the water to form a protective molecular layer on metals in the headspace of a vessel. It also offers protection at the air-water interface.
Other important routine maintenance steps that play a complementary role to corrosion protection for an overall healthier system include control of the formation of scale (insoluble Mg and Ca salts) and biofilm (surface-attached microbial communities). Like corrosion (or perhaps even worse than corrosion), scale can reduce water flow and heat-transfer efficiency, making the system work harder with the potential for burnout. A scale inhibitor should therefore be part of the normal water treatment package, while a full descaling process is helpful every few years or as needed. Cooling systems also face a constant battle against biofilm buildup that hinders heat-transfer efficiency and limits the access of corrosion inhibitors to the metal surface. During peak season, frequent biocide treatment is routine. Pretreatment with a bio-dispersant can help loosen the biofilm, making it easier to treat and flush out of the system [ 4].
Scheduled maintenance
Many large facilities, such as petroleum refineries, power plants or fertilizer plants, have periods of scheduled maintenance or “turnarounds” where some or all of the plant is shut down for maintenance or new equipment installation. This inevitably slows production and raises the risk of corrosion on idle equipment. For example, one power plant in the U.K. regularly experienced problems with rust forming on boiler tubes and walls during scheduled maintenance. The rust would spew out of chimneys when the boilers were restarted, causing problems for area businesses and forcing the power station to turn the boilers off until a change in the wind made it safe to turn them on again [5]. At another power plant in the U.K., two out of five heat-recovery steam generators (HRSGs) needed to be shut down for several months. Their tube banks and header modules needed preservation during this time [6]. Without protection, they faced the risk of reduced integrity and service life, with the possibility that the HRSGs might not be immediately ready to return to service when needed. In both cases, corrosion protection was vital to eliminate further delays and unnecessary losses.
Potential protection deficiencies
Often, methods such as nitrogen purge, dehumidification and desiccant placement are used to protect offline systems, but they all have disadvantages. Nitrogen blanketing requires constant monitoring, is expensive and must be replenished when pressure is lost. It also poses extreme dangers to workers who unwarily enter an area where nitrogen has leaked. Dehumidification systems require a constant source of power and are a passive form of protection that may or may not be sufficient to quell the corrosion process. Desiccants are similar because they are limited to how much moisture they can pull out of the atmosphere. Moreover, they often must be removed before startup to avoid serious problems.
And while VCIs must remain enclosed in a boiler or cooling system, they do not require an airtight seal to remain effective. Reapplication is often unnecessary even if the system is periodically opened for monitoring. VCIs are much more cost-effective than nitrogen blanketing, often with lower risks to workers, depending on the specific chemistry used. Because they vaporize and diffuse throughout the enclosure, forming a protective molecular layer on metal surfaces, VCI protection is comprehensive and easy to apply. VCIs typically do not need to be removed before startup, allowing for a faster return to service to maximize uptime.
Protecting redundant systems
As mentioned previously, the best plan for recovering from failure or unplanned maintenance on a boiler or cooling water system is to have a backup ready to keep the power on or the chemical processes going until the primary equipment can be repaired. For true reliability, that also means having corrosion protection in place while the systems are in dry layup, wet layup or on standby.
For boilers, keeping the system on low-fire for standby is the fastest path to service because the boiler remains filled with water that is partially heated. Just a little extra time is needed to heat the water to its operating temperature and start creating the necessary steam. Unfortunately, boilers on standby are often the most difficult to protect against corrosion. The traditional method is to treat the water with sulfites and maintain a high pH, a process that requires frequent monitoring and adjustment and therefore is often neglected, leading to the corrosion that should have been avoided in the first place. Furthermore, even if pH is maintained, the headspace above the water is not protected. Multiphase VCI inhibitors that are stable at temperatures up to 300°F (150°C) are a good option for these situations because they offer comprehensive protection without requiring frequent monitoring, and make it easy to quickly return the boiler to operating temperature.
For situations where the boiler needs to remain filled but does not need to stay warm, a wet layup at room temperature may be optimal, saving the extra energy needed to constantly keep the system warm. Again, VCIs are helpful since the metal surfaces can be protected both above and below the water level. At other times, a dry layup where the boiler is completely emptied and filled with a water-soluble VCI powder or fogged with a waterborne VCI is best, as in the case of an extended layup or when winter conditions pose freezing concerns. Whatever the scenario, special removal of the corrosion inhibitors is usually unneeded, facilitating an easy return to service.
Which ingredients do you need?
Boiler and cooling system redundancy is an important ingredient in the maintenance recipe for plant reliability and must be backed up by a solid corrosion prevention system during operation and layup for best results. High-performance corrosion inhibitors like VCIs make this possible without some of the complications and deficiencies inherent in some other methods of protection. Their ease of use and effectiveness present a potentially huge return on investment that directly correlates to the value of the commodities produced in the industries where they are used. ■
Acknowledgement
All images provided by Cortec
References
1. Siemens AG, The True Cost of Downtime 2024, Article No. DICS-B10146-00-7600 PDF DÖ, 2024, https://assets.new.siemens.com/siemens/assets/api/uuid:1b43afb5-2d07-47f7-9eb7-893fe7d0bc59/TCOD-2024_original.pdf.
2. Dispel, How Digital Transformation Reduces Unplanned Downtime in the Energy Sector, blog post, 16 March 2021, https://dispel.com/blog/how-digital-transformation-reduces-unplanned-downtime-in-the-energy-sector.
3. Cortec, Preventing Corrosion in Chiller System Vacuum Pump, Case History 805, May 2023, http://www.corteccasehistories.com/.
4. Cortec, Fighting Summer Biofilm Problems with BioClean 612, News Alert, 13 June 2023, https://www.cortecvci.com/news-alert-fighting-summer-biofilm-problems-with-bioclean-612/.
5. Cortec, Preservation Solutions for Rusty Power Plant, Case History 649, December 2019, http://www.corteccasehistories.com/.
6. Cortec, Layup of Power Station Heat Recovery Steam Generators, Case History 750, December 2021, www.corteccasehistories.com/.
Authors
Julie Holmquist (Email: jholmquist@cortecvci.com) has been a content writer at Cortec Corp. since 2015. She specializes in writing about corrosion-inhibiting technology for a variety of industries, including manufacturing, oil and gas, power generation and water treatment.
Scott Bryan (Email: sbryan@cortecvci.com) is Cortec’s technical sales manager for water treatment products. He has almost 30 years of experience in the water treatment industry. Bryan has maintained his qualifications as a Certified Water Technologist (CWT) since 2005. For 15 years, Bryan worked as a distributor for Cortec water treatment solutions before joining Cortec in 2019.