Organic cycle chemistry based on film-forming substances (FFS) is being considered more frequently as an alternative to conventional corrosion-treatment programs. Here’s what you need to know about using FFS to inhibit corrosion throughout the water and steam circuits of fossil and combined cycle/heat recovery steam generator plants. It should be noted that a well controlled, traditional chemistry program is a heavily favored, first choice for most plants.
Film-forming substances (FFS) are a range of corrosion-inhibiting products for boiler chemistry. This category includes Film-forming amines (FFAs), which have been used since the 1960s and other film forming substances. These early substances required the use of a carrier chemical due to lack of solubility. A carrier like cyclohexamine was added to the product for this purpose and not used on high pressure boilers due to thermal decomposition.
Recently, products have been developed that do not increase cation conductivity, even on higher pressure boilers. Organic cycle chemistry based on FFS, particularly FFAs, is being increasingly employed as an alternative to conventional treatment programs because they inhibit corrosion while maintaining clean heat transfer surfaces.
What are film forming substances?
FFS inhibit corrosion by forming a very thin, non-wetable film on the surface of power plant equipment, which acts as a barrier between the metal surface and the water/steam phase that may help your plant:
- Reduce corrosion in continuous operation
- Minimize corrosion product transport
- Protect plant from corrosion during shutdown/layup
Advantages of FFS
Potential Advantages of FSS over other types of corrosion control include:
- Insensitivity to load transients, frequent start/stop operation and during shutdown periods
- Improves wet and dry conservation during shutdown/layup
- Lowers concentrations of corrosion products
- Reduces flow accelerated corrosion (FAC), especially in heat recovery steam generators (HRSGs) and air-cooled condensers (ACCs)
- Lowers release of corrosion products during startup
What to do before adopting an ffs program
If the plant is operating successfully within IAPWS, EPRI and other regulatory body guidelines, and meeting the corrosion product transport levels, then there is no need to consider these products. If corrosion product transport levels are not meeting guidelines, then an investigation into why should be completed. Typical causes for not meeting corrosion product requirements include:
- operating with chronic contamination
- high levels of air in leakage
- non-optimized chemistry program
- insufficient layup practices
After identifying a potential FFS, it is important to ask the following questions before implementation:
- Do I have good baseline corrosion product data?
- What is the main steam unit temperature and what is the thermal stability of the FFS?
- Does the product interfere with the measurement of cycle chemistry instrumentation probes?
- Does the product form gunk balls during operation?
- What happens if the product is accidentally overfed?
- How does this product impact plant safety rules and environmental permits?
- What type of agency approval is required to feed this product?
- Is the product compatible with other chemicals being used?
- How will residual concentrations of the product in the cycle be measured?
- What is the feedrate of the product during initial feed and what’s the impact the cycle once filmed?
- How will I know all my systems have been filmed?
- What equipment will be needed to feed the product?
- Where should the product be injected?
Not asking these questions – or not receiving satisfactory answers from the supplier – can result in an unknown chemical or chemicals being added to the steam/water cycle and potentially jeopardize your entire system.
How to customize an ffs to your plant
To control corrosion throughout the water and steam circuits of your plant, it’s essential to implement and optimize a chemical treatment plan that’s been customized to your specific needs.
- Identify and monitor key performance indicators prior to and during the application.
- Understand current plant conditions.
- Carefully monitor and control aspects to avoid failures and damage.
- Determine a baseline by measuring key indices for the cycle chemistry before FFS application.
- Monitor and record key parameters, including:
- Condensate CACE, dissolved oxygen, sodium
- Feedwater pH, dissolved oxygen, cation conductivity
- Drum pH, specific conductivity, CACE/chlorides
- Main, reheat, or HP steam sodium and CACE
- Condensate iron and copper and aluminum, if applicable
- Product residual
Guidelines for monitoring and sampling
The only way to effectively evaluate the effectiveness of FFS is to have a large body of data on the corrosion product transport of your system. This requires a well thought-out, implemented and QA/QC checked corrosion product sampling program with data taken before switching, during implementation and during ongoing utilization.
- Ideally samples should be taken during steady high load conditions maintained for minimally 3-4 hours and should vary in times taken daily.
- The monitoring should last for at least one month prior to the FFS application, ensuring the metal/oxide surfaces are stabilized.
- The frequency of sampling for corrosion product monitoring should be considered with a once per week minimum.
- On startup, corrosion product sampling should be performed at the same point on each startup.
- Comparison of the measurements of total iron (and total copper) to the target values provides baseline values and an indication effectiveness.
Could an FFS program control corrosion in your plant? Find out if FFS is right for you by contacting us at +1-262-567-7256, or complete our online contact form for more information.