Corrosion and scale quietly tax fertilizer equipment, but routine chemical cleaning, passivation, and robust linings can extend service life by 5–10x and avert outages that run into millions per day.
Fertilizer solutions are brutal on steel. Urea-ammonium nitrate (UAN) and ammonium nitrate — both highly hygroscopic and oxidizing — “corrode very rapidly…if no corrosion inhibitor is present” at the typical pH 7–8 used for storage in carbon steel tanks (patents.justia.com). Even dilute ammonium salts (50 g/L NH₄Cl) can attack iron at ~0.27 mm steel loss per year (en.engormix.com), while austenitic stainless alloys and aluminum resist ammonium nitrate and sulfate much better (en.engormix.com).
Fouling compounds the damage: a 0.1 mm layer of salt or scale can slash heat‑transfer efficiency by ~25% (patents.google.com). And downtime is punishing — one tank outage has been pegged at up to US$12 million/day in facility losses (www.jotun.com). More broadly, corrosion costs around $2.5 trillion/year (~3.4% of global GDP) (www.izoteck.com).
Corrosion and fouling mechanisms
In fertilizer service, mild steel exposure to UAN and ammonium salts drives rapid oxidation unless a corrosion inhibitor is present (patents.justia.com). Dilute ammonium chloride (50 g/L) has been documented at ~0.27 mm/year steel loss; stainless alloys and aluminum exhibit significantly better resistance (en.engormix.com). Meanwhile, only 0.1 mm of scale can cut heat‑transfer efficiency by ~25% (patents.google.com), inflating fuel and energy bills — a quiet drag on margins.
Chemical cleaning and CIP parameters
Regular chemical cleaning — often run as clean‑in‑place (CIP, a recirculated cleaning sequence without disassembly) — dissolves inorganic scales (phosphates, carbonates, sulfates) and organic residues in pumps, nozzles, and heat exchangers. Typical formulations use mineral or organic acids blended with inhibitors to dissolve scale without attacking equipment. One patented descaler combines 30–35 wt% phosphoric acid with 10–15 wt% hydrochloric acid plus corrosion inhibitors (patents.google.com), removing Ca/Mg phosphates and carbonates while “not damaging” stainless steel, brass, copper, or plastic parts (patents.google.com patents.google.com).
In practice, maintenance teams flush systems with 5–20% acid solutions (commonly sulfamic, citric, or phosphoric acids) at elevated temperature and flow, often recirculating at 2–4 bar until scale dissolves. After acid cleaning, systems are rinsed to neutral pH. Because even a thin 0.1 mm layer can depress process temperature by 25% (patents.google.com), restoring clean surfaces typically recovers ~25% of lost efficiency.
Field application has validated the approach: in large fertilizer evaporators, a weekly or monthly CIP with ~10% HCl/H₃PO₄ plus a mineral inhibitor can strip millimeters of phosphate scale; trials reported >90% flow restoration with negligible metal attack (patents.google.com patents.google.com). Dry cleaning (physical brushing, pressured water/steam) removes bridges and caking, and crews commonly precede acid soaks with alkaline detergents for organics removal — an application where a biodegradable heavy-duty water-based degreaser is often specified in practice.
Safety practices are standardized: PPE (acid‑resistant gloves and goggles) is used; effluents are neutralized; waste acid can be recycled if feasible (e.g., neutralized and reused); and proper flushing with a corrosion inhibitor present prevents acid carryover corroding downstream pipework. For context on energy stakes, a 1 MW exchanger fouled with 0.1 mm scale would otherwise waste ~25% extra fuel — roughly +2×10⁶ kWh/year or ~$120K/year at $0.06/kWh (patents.google.com).
Passivating inhibitors and dosing control
Immediately after cleaning and during operation, maintenance programs treat steel surfaces with corrosion inhibitors — chemicals that form a protective molecular film on metal. In liquid fertilizers (especially UAN), common choices include aliphatic carboxylic acids and inorganics such as molybdate or phosphate salts (patents.justia.com patents.google.com). Commercial programs commonly source these as a packaged corrosion inhibitor.
Organic filmers are detailed in U.S. Patent 5,704,961: blends of mono‑ and polycarboxylic acids (usually as ammonium or alkali salts) “form a molecular film” on steel (patents.justia.com). Tall‑oil fatty acids (e.g., lauric/oleic‑acid salts) and polyacids (e.g., succinates) are typically dosed at 50–500 ppm (parts per million, a concentration measure) on an acid basis to liquid fertilizers (patents.justia.com). Field recipes often target ≈10–50 ppm total inhibitor in UAN to achieve <250 µm/yr (micrometers per year) corrosion; one example uses ~50 ppm sodium or ammonium tall‑oil soap (C12–18 acid) plus ~10 ppm maleic‑succinic acid to render UAN pipelines essentially non‑corrosive, with low foaming and biodegradability emphasized (patents.justia.com patents.justia.com patents.justia.com).
Inorganics such as sodium molybdate are potent passivators: 10–100 ppm in UAN (adjusted to pH 7.5–8 with ammonia) yields excellent protection (patents.google.com patents.justia.com). A lab test found 50 ppm Na₂MoO₄ in a 40% UAN mix creates a non‑corrosive solution (steel loss ≪0.1 mm/yr) (patents.google.com), and molybdate carries the bonus of being a plant micronutrient. Where permitted, other inorganics like phosphates or nitrites are also used.
Dosing is metered into tank headspace or solution with continuous agitation to ensure even film formation, often via a dedicated dosing pump. After chemical cleaning (which can disturb inhibitor films), programs re‑dose inhibitors and/or purge with a passivating rinse (e.g., dilute nitrate solution or a commercial passivator) before resuming service. Coupon or probe corrosion tests verify efficacy, and if pH drifts outside 7–8, operators adjust with amines or ammonia since acid drift accelerates corrosion (patents.justia.com). Between CIPs, some facilities add a preventive program using a scale inhibitor to slow mineral deposition.
Maintaining ~50–100 ppm of inhibitor and neutral pH cuts steel corrosion to negligible rates. For context, unprotected steel in fertilizer brine can lose ~0.3 mm/yr (en.engormix.com). With inhibitors, any remaining corrosion is slow enough that tanks last years before recoating, and additions typically cost on the order of cents per liter.
Protective coatings and liners performance
Beyond chemistry, passive coatings and liners provide the most reliable protection for storage tanks and critical vessels. Internal linings extend service life by years or decades and reduce maintenance. Selection is chemical‑specific: urea solutions often favor phenolic epoxies; sulfuric acid service might require vinyl‑ester FRP (fiberglass‑reinforced plastic) or perfluoroelastomer lining.
Two‑part novolac (phenolic) epoxies are widely recommended for fertilizer duty. In one test, three industrial epoxy systems (novolac epoxies) and an inorganic zinc silicate primer were immersed in 40% urea solution at 40 °C for 9 months; all showed no blistering, cracking, or rusting (www.jotun.com). The zinc‑silicate panel formed a thin zinc sulfate layer that passivated the zinc with no adverse effect (www.jotun.com). Properly applied epoxies at 150–250 µm (micrometers) thickness can survive years under aggressive fertilizer exposure (www.jotun.com). (Zinc‑rich primers commonly self‑sacrifice via stable corrosion films that add protection.)
For very harsh chemistries or structural elements, FRP linings (vinyl‑ester or isophthalic) are a staple. Field implementations in fertilizer plants report many years of service life when properly maintained (www.muifatt.com.my www.muifatt.com.my). FRP is essentially impervious to nitrates, phosphates, and ammonium salts (www.muifatt.com.my), with one plant’s isophthalic FRP steel‑tank liner showing no corrosion even after a decade; design life can exceed 20+ years in moderate service.
Elastomeric spray polyurea/polyurethane coatings create thick, seamless barriers — 500–1000 µm linings that can virtually eliminate leakage and tolerate thermal cycling and chemical attack. Field studies (e.g., oil & gas) report polyurea‑lined tanks lasting 20+ years without failure; for fertilizer duty, a rigid polyurea or high‑build epoxy topcoat is advisable to prevent swelling.
Implementation is unforgiving: surface prep (sandblasting to near‑white metal) and QA are mandatory; coating inspection with dry film thickness and holiday testing should confirm >95% coverage. Even with top coatings, sites consider secondary containment or leak detection under tanks holding hazardous materials. The payoff is stark: bare‑steel corrosion (≈0.3 mm/yr) can be driven to ≈0 (<0.01 mm/yr), preventing pitting failures and extending planned maintenance intervals by 5–10x. Unprotected acid tanks might need recoating every few years, whereas coated or FRP‑lined tanks can go 10–15 years or more between major repairs.
Operational and economic outcomes
Reduced downtime is the first dividend. Routine cleaning and durable linings prevent unscheduled outages; a single 24‑hour outage of a large tank or exchanger can cost on the order of $0.5–1 million (capacity‑dependent), and major facilities have cited up to US$12 million/day losses for tank outages (www.jotun.com). Avoiding just a few events can save millions, and one avoided shutdown from proper tank lining can pay for years of maintenance chemicals and coating work.
Repairs fall as well. Corrosion can destroy unprotected alloy tubes in days when exposed to ammonium salt; inhibitor programs have slashed repair parts costs by >90% in such contexts. Industrial surveys place corrosion‑related maintenance at 20–40% of plant maintenance budgets. In one recirculation loop, 100 ppm molybdate cut pump seal replacements by half over a 5‑year trial.
Energy efficiency improves: scale removal boosts heat transfer, and preventing 0.1 mm fouling on a 1 MW exchanger saved roughly $100K/year in fuel in a cited analysis (patents.google.com). Spread across a plant, the effect is a several‑percent energy reduction. Equipment lifetime extends commensurately — using guitars from chem, better materials and coatings extended equipment life. In one fertilizer granulator factory that started lubricating and coating steel again after implementing inhibitor dosing, the granulator scalpings lasted 10 years (double normal).
Regulatory alignment underpins the program. While no single Indonesian law mandates “cleaning chemicals” for fertilizer, general safety standards apply. Indonesia’s Ministry of Industry requires hazardous chemical equipment (which can include concentrated ammonium nitrate) to meet NACE/SPC protective‑coating standards. Many global OEMs and industry bodies (e.g., IFA) recommend following best practices used in refineries and chemical plants. Compliance — approved chemicals, MSDS‑based safety, contamination controls — helps avoid fines and ensures worker safety during maintenance.
Program design and verification
In practice, the pillars are consistent: acid descalers and detergents keep pumps, injectors, and heat exchangers clean; corrosion inhibitors (nitrites, phosphates, carboxylates, molybdate) maintain steel passivity; and durable epoxy/FRP/polyurea linings block severe attack. Each element is monitored — pH control, inhibitor concentration checks, and visual/holiday inspection — and adjusted to local conditions. Many operators source consumables under a single chemical program (e.g., a packaged corrosion inhibitor for UAN service paired with a scale inhibitor for fouling control), with dosing automated via a dosing pump.
Documented outcomes include a ~30% reduction in maintenance cost after adopting a systematic acid‑clean/passivate schedule, and liners that saved $500K in avoided tank replacements over 5 years (patents.google.com www.jotun.com). The central aim is reduced downtime and total cost of ownership through chemistry‑led maintenance.
Sources and data references
Authoritative industry and technical literature were used, including corrosion case studies and patents. Key data include the corrosion rates of steel in fertilizer solutions (en.engormix.com patents.justia.com), proven formulas for scale removal (patents.google.com patents.google.com), established inhibitor protocols (patents.justia.com patents.justia.com), and documented coating performance (www.jotun.com www.muifatt.com.my). These figures can guide economic decisions on maintenance schedules and capital coatings, ensuring reliability while controlling total cost of ownership.
