How to Use Filming Amine (Octadecylamine) in Boiler and Condensate Systems

Overview

Filming Amine, most commonly octadecylamine (ODA, CAS 124-30-1) or related long-chain aliphatic amines (C16–C18), is a unique class of corrosion inhibitor used specifically to protect steam condensate return lines and steam distribution systems in industrial boiler operations. Unlike conventional water-soluble corrosion inhibitors that protect by forming ionic complexes at metal surfaces, filming amines work by adsorbing onto the metal surface through their polar amine group (–NH₂) while the hydrophobic octadecyl (C18) hydrocarbon tail orients away from the surface. The result is a monomolecular, wax-like hydrophobic film that repels water, oxygen, and carbonic acid (H₂CO₃) from the metal surface — providing mechanical barrier protection rather than electrochemical passivation.

The primary corrosion threat in steam condensate systems is carbonic acid attack. CO₂ dissolved in the boiler feedwater passes through the boiler as gas with the steam, dissolves in the condensate water at lower temperatures, and forms carbonic acid — with a resulting condensate pH as low as 4.5–5.5. At this pH, carbon steel corrodes rapidly, producing characteristic grooving or generalized thinning of condensate pipes. Without treatment, condensate system corrosion is one of the leading causes of unplanned boiler shutdowns and premature pipe replacement. ODA eliminates this threat by coating the entire condensate system with a hydrophobic barrier that carbonic acid cannot penetrate.

A critical operational feature of filming amine is its volatility. When dosed into the boiler feedwater or steam drum, ODA vaporizes with the steam and travels through the entire steam distribution system — reaching heat exchangers, steam traps, condensate return headers, and feed tanks — depositing its protective film wherever steam condenses. This means a single dosing point at the boiler or deaerator can protect the entire downstream condensate system without the need for distributed injection points. ODA is approved by the US FDA for use in steam that contacts food-grade process equipment (when used within prescribed limits), making it suitable for food processing, dairy, and beverage manufacturing facilities.

Preparation & Dissolution

Octadecylamine is supplied as white to off-white solid flakes or pastilles with a melting point of 50–55°C. Unlike water-soluble inhibitors, ODA is essentially insoluble in cold water and requires special preparation to form a stable, pumpable emulsion:

Melt the ODA — Heat the required quantity of ODA flakes in a stainless steel or HDPE vessel to 60–70°C until completely melted. Use a steam jacketed tank or water bath; avoid open flame heating as ODA has a flash point of ~185°C.
Prepare emulsifier solution — In a separate vessel, prepare a solution of emulsifier (typically a nonionic surfactant such as ethoxylated alcohol or the specialized ODA emulsifier provided by the supplier) in warm water (50–60°C). The emulsifier-to-ODA ratio is typically 1:4 to 1:8 by weight.
Emulsify with high-shear mixing — Slowly pour the melted ODA into the warm emulsifier solution (NOT the other way around) while applying high-shear mixing (propeller mixer, homogenizer, or recirculation pump with in-line mixer). Continue until a stable, milky white emulsion forms — typically 15–30 minutes.
Dilute to working concentration — Add warm water slowly to achieve the target emulsion concentration, typically 5–15% ODA by weight. The emulsion should be stable (no phase separation) when cooled to ambient temperature.
Many suppliers offer pre-made ODA emulsions (typically 30–50% active content) which greatly simplifies preparation. Simply dilute with warm water to the target feed concentration before use.
Do not allow ODA emulsions to freeze as phase separation occurs and the emulsion cannot be re-homogenized. Store above 5°C.

Dosing Guide

Application	ODA Dose	Notes
Steam condensate system — initial passivation	5–10 ppm ODA in feedwater for 2–4 weeks	Higher dose builds up the initial film; critical for new or recently cleaned systems
Steam condensate — steady-state maintenance	1–3 ppm ODA in feedwater	Maintains continuous film against CO₂ and O₂ attack
Systems with high CO₂ in condensate (pH < 6.0)	3–5 ppm ODA + neutralizing amine co-treatment	Combine with morpholine, cyclohexylamine, or DEAE to raise condensate pH
Boiler feedwater total program	1–3 ppm ODA + 50–100 ppm sodium sulfite or DEHA (O₂ scavenger)	ODA for film; O₂ scavenger for dissolved oxygen removal
Once-through steam generator	0.5–2 ppm ODA	Lower dose due to short contact time; verify condensate iron < 0.1 ppm Fe
Food-grade steam (FDA-regulated)	Max 3 ppm ODA in steam	Verify with FDA 21 CFR 173.310; use only ODA of appropriate purity

Application Procedure

Prepare the ODA emulsion — Either prepare from flakes as described above or dilute a commercially available pre-made emulsion to a convenient working concentration (typically 5–10% ODA). Allow the emulsion to equilibrate to ambient temperature before dosing.
Select the dosing point — The optimal dosing point is the feedwater line upstream of the boiler or the deaerator outlet. ODA dosed here vaporizes with steam and deposits film throughout the system. Avoid dosing into the boiler drum directly (foaming risk) or into the condensate return line only (incomplete system coverage).
Commission a dedicated metering pump — ODA emulsion is viscous and can clog standard metering pumps. Use a progressive cavity or diaphragm pump with PTFE or stainless steel wetted parts and PTFE-lined tubing. Keep the pump and tubing warm (above 15°C) to prevent emulsion destabilization.
Set initial passivation dose — For the first 2–4 weeks, dose at 5–10 ppm ODA in feedwater to rapidly build the protective film throughout the system. Monitor condensate iron (Fe) levels: a transient spike in iron during the first few days is normal as existing corrosion products are lifted by the amine; continuing high iron (> 0.5 ppm after 2 weeks) indicates inadequate film coverage.
Transition to maintenance dose — After passivation, reduce to 1–3 ppm ODA in feedwater. Monitor condensate pH and iron monthly to confirm adequate ongoing protection.
Co-treat with neutralizing amine if condensate pH is low — If condensate pH remains below 7.0 despite ODA treatment, add a volatility-matched neutralizing amine (morpholine, cyclohexylamine, or diethylaminoethanol/DEAE) to chemically neutralize CO₂ and raise condensate pH. ODA raises pH indirectly by excluding water; neutralizing amines raise pH directly by reacting with H₂CO₃.

Monitoring & Control

Parameter	Frequency	Target
Condensate pH (at return header)	Daily	≥ 8.0 (> 8.5 if using neutralizing amine combination)
Dissolved iron in condensate (Fe total)	Weekly	< 0.1 ppm Fe indicates excellent film coverage; > 0.3 ppm indicates film gap
ODA residual in feedwater (colorimetric or GC)	Weekly	1–3 ppm ODA maintained at dosing point
Dissolved oxygen in feedwater (pre-boiler)	Daily	< 0.007 ppm (7 ppb) — ODA cannot compensate for high dissolved O₂; use O₂ scavenger
Condensate conductivity	Daily	Sudden increase indicates boiler water carryover or contamination event
Corrosion coupon rate (condensate header)	Quarterly	< 0.5 mpy mild steel

Common Mistakes

Dosing ODA without removing dissolved oxygen first: ODA's hydrophobic film is highly effective against carbonic acid corrosion but does not provide reliable protection against dissolved oxygen (O₂) pitting. Oxygen causes aggressive, localized pitting at film discontinuities. Always combine ODA with an oxygen scavenger (DEHA, sodium sulfite, carbohydrazide) and ensure the deaerator is functioning correctly (feedwater dissolved O₂ < 7 ppb). Treating condensate corrosion with ODA alone while neglecting oxygen is a common and expensive mistake.
Allowing the ODA emulsion to freeze or separate: ODA emulsions stored below 5°C undergo phase separation that cannot be reversed by warming or mixing. The separated oil phase can block dosing lines and metering pump heads, causing loss of protection. Ensure heated storage for the emulsion drum in cold climates, and inspect the emulsion visually (milky white, uniform) before each fill of the day tank.
Skipping the initial high-dose passivation period: Engineers who immediately dose at maintenance levels on a new or corrosion-damaged system never build adequate film coverage. The initial 2–4 weeks at high dose (5–10 ppm) are essential for establishing a complete monolayer across all metal surfaces in the condensate circuit. Skipping this phase results in a patchy film with gaps that become focal points for accelerated corrosion.
Not monitoring condensate iron as the primary performance indicator: ODA residual at the dosing point tells you what was fed, not whether it reached and adhered to the condensate piping. Condensate iron is the definitive outcome indicator — iron < 0.1 ppm confirms that the film is complete and the system is protected. Many operators track ODA feed rate but never measure condensate iron, missing the most important signal in the monitoring program.
Using ODA in systems with excessive condensate contamination (oil, process chemicals): Filming amines are effective on clean metal surfaces. If condensate is contaminated with hydrocarbon oils, process chemicals, or high levels of hardness from cooling water ingress, these contaminants coat the metal surface before ODA can adsorb and prevent film formation. Before relying on ODA, identify and eliminate condensate contamination sources. Condensate polishing (activated carbon, ion exchange) may be needed in heavily contaminated systems.

Storage & Handling

Shelf life: 2 years for dry flakes in original sealed packaging; ODA emulsions 12 months if stored above 5°C
Temperature: Store dry ODA above ambient (melting point 50–55°C); keep emulsions between 5°C and 40°C to prevent freezing or emulsion breakdown. Use insulated or heated storage in cold climates
Container: Dry ODA in original PE-lined bags or fiber drums; emulsions in HDPE drums or IBC totes with PTFE-lined fittings
Safety: ODA has moderate acute toxicity and is irritating to skin, eyes, and respiratory tract. Wear chemical-resistant gloves, safety glasses, and face shield when handling melted ODA or concentrated emulsions. Melted ODA can cause thermal burns in addition to chemical irritation. Flash point ~185°C — avoid open flames near molten material. Aquatic toxicity: ODA is harmful to aquatic organisms; prevent spills from reaching waterways.