Fertigation and chemigation are booming, but low pH and oxidizers can chew through metals, elastomers and plastics fast. New data and compatibility charts point to smarter material picks and a flush-first maintenance playbook.
Modern fertigation and chemigation — injecting soluble fertilizers, acids, disinfectants or pesticides into irrigation — are growing rapidly, with a global market of about ~$11 B in 2021 and roughly ~8% CAGR to 2027 (bisresearch.com). The upside in efficiency is clear; the downside is less visible until a pump housing pits out or a seal swells.
Corrosive fertilizers, acidifiers and oxidizers attack pump housings, valves and seals. In a representative data point, Cahoon (2002) measured mild‑steel corrosion in a typical 28‑0‑0 UAN (urea ammonium nitrate) solution: at neutral‑to‑mildly acidic pH (3–8.5) corrosion was ∼2 mm/yr, versus ~92 mm/yr at pH ≈1 (researchgate.net). Low pH or high oxidative potential drastically accelerates wear; in practice, even resistant materials can pit, crack or swell over time.
Selecting the right alloys, plastics and seals — and adopting an aggressive flush schedule with a metering setup such as a dosing pump — is increasingly the line between multi‑season reliability and surprise downtime.
Material compatibility under common injectants
Stainless steel (SS 300‑series). Grades 304 and 316 are common in pumps and fittings. The high Cr/Ni content gives good general resistance. Ammonium and nitrate salts are essentially benign: 304 SS rates “A (no effect)” with dilute NH₄NO₃ or (NH₄)₂SO₄ (blog.darwin-microfluidics.com). By contrast, chlorides and strong acids are problematic. Calcium chloride will aggressively attack 304 SS (ag.purdue.edu). In practice, 316 SS (with added Mo) is used for highly acidic or chloride‑laden solutions; 304 tolerates many conditions (including inorganic acids), whereas 316L is recommended for hot or highly acidic streams (ag.purdue.edu). Industry guidelines advise 316 (or higher) for calcium chloride and other low‑pH media (ag.purdue.edu).
Chloride‑induced pitting and stress‑corrosion cracking of austenitic SS can occur if free chlorine or salt is present; bench data show only slight effect at low Cl₂, but higher concentrations can initiate cracking (blog.darwin-microfluidics.com) (extension.uga.edu). Welds and crevices are worst spots. In one fertilizer plant, 304 SS intercoolers failed in ~6 months due to ammonia‑CO₂ attack and galvanic coupling — a reminder that uniform material and passive‑film maintenance are essential (researchgate.net).
PVC (polyvinyl chloride). PVC piping is widely used for irrigation mains and injection lines. PVC is remarkably resistant to inorganic chemicals: it tolerates most acids, alkalis and salts (vinidex.com.au). Hence common soluble fertilizers (saline nitrates, phosphates) and low‑concentration acids pose little risk to PVC. However, PVC is attacked by organic solvents, ketones/esters (e.g., acetone) and aromatics; oil‑based pesticides may cause PVC swelling or softening, so an alternative material or internal liner is needed if such chemicals are used (vinidex.com.au). PVC is also UV‑sensitive unless stabilized. Adhesives and joint cements are usually compatible, but rubber gaskets in PVC fittings must be chemically chosen.
Elastomers (Viton, EPDM). Seals and diaphragms in pumps are typically fluoroelastomers (Viton/FKM) or EPDM rubber — with opposite strengths. Viton is formulated for oils, fuels and many organic solvents and earns A/B ratings for aromatic hydrocarbons, ketones and strong acids (rubberandseal.com). EPDM excels with water, steam, alkalis and dilute acids (rubberandseal.com). A rule of thumb in irrigation: use Viton for oil‑based or hydrocarbon chemicals and EPDM for water‑based fertilizers and oxidizing agents. Industry sources emphasize this — EPDM seals are recommended for standard herbicides like glyphosate or atrazine, while Viton seals are mandated for oil‑carrier pesticides (pumpandmeter.com). Viton is one of the few elastomers compatible with concentrated acids (stable in HCl and H₂SO₄) (rubberandseal.com), whereas EPDM will slowly degrade. Note that hypochlorite strongly attacks most rubbers; even Viton will swell or lose strength in strong bleach. Compatibility charts indicate only moderate compatibility with chlorine (wet chlorine gas gives a B) (blog.darwin-microfluidics.com), so seals should be flushed or replaced if exposed.
Teflon (PTFE). PTFE (Teflon) is virtually inert and resists most acids, alcohols, detergents and solvents (blog.darwin-microfluidics.com). Its inertness and thermal stability make it ideal for injection tubing and pump diaphragms; PTFE is widely used for reactive and corrosive chemicals (blog.darwin-microfluidics.com). Notable attack occurs only with highly reactive species like molten alkali or elemental fluorine, not typical in fertigation. PTFE fittings are therefore recommended where doubt exists (cost is higher).
Material selection by chemical application
Soluble fertilizers (nitrates, phosphates, potassium salts). These are largely neutral‑salt solutions. PVC or polyethylene lines are generally fine, and 304 SS can be used in pumps and fittings. Suitable O‑rings include EPDM for water‑based service or Viton if any petroleum surfactant is present. 304 or 316 SS is used for metering pumps and valves; after dosing with a dosing pump, lines should be flushed.
Acid injectants (phosphoric, sulfuric, muriatic acid). Use highly corrosion‑resistant materials. Avoid mild steel or brass. Options include 316 SS or CPVC piping; PVDF or PTFE pump heads; and Viton or PTFE diaphragms/seals (ag.purdue.edu). PTFE tubing is ideal where pH is very low. While 304 SS is MIC/VOC rated for some acids, 316L or CPVC is safer; 316L is typically required for 30–50% phosphoric or sulfuric acid.
Oxidizers/bleach. Sodium hypochlorite bleaches attack virtually all metals (even 316 SS eventually) and degrade elastomers. Best practice is non‑metallic paths (PTFE or PVC, which can handle roughly ~10% bleach) and immediate flushing after use. Metals should be 316 SS or, if continuous use, titanium or Hastelloy. Seals should be Viton; EPDM is destroyed by strong oxidizers.
Oil‑based pesticides/organics. EPDM will swell with these; use Viton or PTFE for hoses, valves and pump seals. Plastic bodies (PVC or polyethylene) are usually fine for dilute sprays if pressure is low, but any sight glass or metal contact should be protected. Brass fittings should be replaced with SS or plastic when using aminated herbicides, as ammonia can stress‑crack brass.
Alkaline or detergent chemistries. Use EPDM or Viton depending on solvent; metals can be steel or SS. Ammonium hydroxide and caustics attack copper/brass, so avoid those in injection equipment.
Corrosion data and cost trade‑offs
Cahoon’s study implies that keeping pH above ~6 in fertilizer lines keeps steel nearly passive (~0.002 mm/yr) (researchgate.net); a drop to pH 2–5 raises rates to a few mm/yr. Upgrading materials often entails a premium: 316 SS costs roughly 30–50% more than 304 by weight (scrap prices ~$0.78 vs $0.56/lb) (mchoneind.com). In chloride or acid service, the longer life of 316 pays off. Similarly, PTFE and Viton spare (~4×) the expense of replacing corroded PVC or nitrile parts.
Maintenance schedule and flushing regime
Immediate flush after fertigation. At the end of each injection event, open downstream emitters and run clean irrigation water until pipes run clear (extension.uga.edu). The irrigation pump should run with the injection pump off while flushing. Using an upstream barrier such as an automatic screen filter reduces debris deposits that interact with chemicals.
Daily/weekly system flush. After normal irrigation, flush submains and laterals periodically. Achieve high velocity (≥0.5 m/s in submains; ≥0.3 m/s in laterals) so settled precipitates or organics are swept out (rivulis.com). Insufficient flushing leads to clogging and eventual system failure (rivulis.com). In practice, run a short (5–10 min) high‑flow flush weekly or after long irrigation cycles; maintenance of a cartridge filter upstream of laterals helps keep particulates in check.
Acid treatment (monthly or as needed). Inject low pH solution to dissolve carbonate scale. Extension research recommends ~45–60 min acid injection to drop pH to ~4–5 (extension.uga.edu). Let lines soak (overnight if possible) for full reaction, then flush thoroughly (extension.uga.edu). Phosphoric acid (10–20%) is common; the volume is set by titration (see example in extension.uga.edu). Frequent mild acidification (just enough to maintain ~pH 6–7 continuously) can also slow scale formation (extension.uga.edu).
Chlorination (seasonal or water‑dependent). Inject sodium hypochlorite to disinfect and remove biofilm. At least once per season, or whenever systems sit idle, inject ~5–6 ppm bleach and circulate for 30–60 min (extension.uga.edu), then flush. If well water is used, chlorinate at end of each cropping cycle (or even each irrigate) to prevent bacteria/algae buildup (extension.uga.edu). Maintain ~1–2 ppm free chlorine contact (sampling below the injection point) for efficacy (extension.uga.edu). Hypochlorite can corrode metals; any stainless components should be rinsed immediately after chlorination, or better yet, drain systems thoroughly. A downstream strainer helps capture loosened biofilm before it reaches emitters.
Routine inspections. Check pump diaphragms, valves and seals for swelling or discoloration. Replace Viton/EPDM parts at the first sign of brittleness or leak. Clean or replace filters and strainers regularly to avoid debris mixing with chemicals. For debris‑rich sources, integrate a manual screen ahead of distribution lines. Winterize by flushing and capping all lines to avoid freeze‑cracking.
Bottom line on longevity
Match materials to chemistry — PVC/304 SS for water‑based nutrients, PTFE/Viton for aggressive organics — and adopt a flush‑and‑don’t‑let‑chemicals‑stand regimen. Data suggest that diligent pH control and flushing can slow corrosion to negligible rates (researchgate.net). Neglect — letting acid or chlorine sit — can eat through components in weeks. Careful material selection plus scheduled acid/bleach flushes will maximize system longevity and reliability, supported by extension and industry guidance, compatibility data and case studies (bisresearch.com) (researchgate.net) (ag.purdue.edu) (pumpandmeter.com) (vinidex.com.au) (extension.uga.edu) (extension.uga.edu) (extension.uga.edu) (blog.darwin-microfluidics.com).
