Chemical Compatibility &
Material Selection Guide
A decision framework for engineers specifying spray nozzles for aggressive media — covering body alloys, orifice inserts, and seal materials for sulphuric acid, hydrochloric acid, nitric acid, halogens, and high-temperature oxidising service. With a full decision matrix and a dedicated section on erosion-corrosion synergy.
Start with the Decision Matrix — it gives a letter-rated compatibility summary for eight common aggressive media across five nozzle body materials and four ceramic/polymer insert options. If the matrix returns an "A" or "B" rating for your chemical, the material is a practical starting point. If the matrix returns "C" or "D", read the corresponding alloy profile section for the specific failure mechanism before dismissing or selecting the material.
The Erosion-Corrosion section applies when your spray liquid contains suspended solids in addition to corrosive chemistry — this combination degrades nozzles faster than either mechanism alone and changes the material selection calculus. The Seal Integrity section covers O-ring and gasket selection for the nozzle assembly itself, which is a separate decision from the body material.
Body Material vs. Chemical Environment
Ratings: A = Excellent (full-concentration service, no known limits at ambient) B = Good (suitable with concentration or temperature constraints — see notes) C = Limited (short-term or low-concentration service only — consult engineering) D = Not recommended
| Chemical Environment | SS 316L | Hastelloy C-276 | Tantalum | Alloy 20 | Titanium Gr. 2 | PTFE / PVDF Body | PEEK Body | Notes |
|---|---|---|---|---|---|---|---|---|
| Mineral Acids | ||||||||
| Sulphuric acid <10% | B | A | A | A | C | A | B | 316L pits above 5% at elevated temp; Titanium reacts above 3% |
| Sulphuric acid 10–70% | D | A | A | B | D | A | B | The dangerous mid-range — most alloys fail here; Hastelloy C-276 and Tantalum are primary options |
| Sulphuric acid >70% (fuming) | B | B | A | C | D | C | D | Concentrated H₂SO₄ passivates SS; PTFE swells in oleum service |
| Hydrochloric acid (all conc.) | D | A | A | B | D | A | B | HCl aggressively attacks SS and Titanium at any concentration; Hastelloy C-276 is the standard metal choice |
| Nitric acid <65% | A | B | A | A | A | A | B | 316L SS and Titanium are well-suited; Hastelloy C-276 is actually inferior to SS in oxidising HNO₃ |
| Nitric acid >65% (fuming) | B | D | A | B | A | B | D | Hastelloy C-276 is attacked by strongly oxidising HNO₃ — a critical counter-intuitive exception |
| Phosphoric acid | B | A | A | A | A | A | B | 316L marginal above 85°C; halide contamination in wet process H₃PO₄ shifts preference to Hastelloy C-276 |
| Alkalis & Oxidisers | ||||||||
| Caustic soda NaOH (all conc.) | A | B | D | A | B | A | A | Tantalum is rapidly attacked by strong alkalis — a critical limitation; 316L SS is the standard choice |
| Sodium hypochlorite NaOCl <2% | B | A | B | B | B | A | B | 316L marginal above ambient temperature; Hastelloy C-276 preferred |
| Sodium hypochlorite >2% | D | A | C | C | C | A | B | Concentrated bleach attacks most alloys; PVDF preferred for polymer body; Hastelloy C-276 for metal |
| Halogens & Solvents | ||||||||
| Hydrofluoric acid HF | D | C | D | D | D | A | B | HF attacks all common metals including Tantalum and Titanium; PVDF or Monel are the metal exception; PTFE/PVDF polymer bodies are the primary choice |
| Chlorinated solvents | B | A | A | B | B | B | A | Check specific solvent; CH₂Cl₂ and CHCl₃ swell some polymers; PEEK is more solvent-resistant than PTFE |
| High-Temperature & Mixed Service | ||||||||
| Seawater / high-chloride brine | C | A | A | B | A | A | B | 316L pits above Critical Pitting Temperature (15–25°C in seawater); Duplex SS or Hastelloy C-276 preferred above ambient |
| Mixed acid (H₂SO₄ + HNO₃) | D | C | A | C | B | A | D | Nitrating acid service — Tantalum and Titanium are primary metallic options; PTFE body where temperature permits |
This Matrix Is a Starting Point, Not a Final Specification
Corrosion rates depend on temperature, concentration, flow velocity, surface finish, and galvanic coupling to adjacent metals — none of which are captured in a letter rating. Use this matrix to identify candidate materials, then consult the alloy profile sections and contact NozzlePro engineering for a site-specific recommendation based on your operating conditions.
Erosion-Corrosion: When Chemical Attack and Mechanical Wear Combine
The decision matrix above rates materials for pure chemical attack. In real spray applications involving abrasive slurries, catalyst fines, or particulate-laden process streams, the correct material selection is different — because erosion-corrosion is not the sum of two independent damage rates. It is a synergistic mechanism in which each process accelerates the other.
The Synergy Mechanism
Metal alloys resist corrosion primarily through a passive oxide film on their surface — a few nanometres of stable oxide that slows ion dissolution by orders of magnitude. This film is the reason Hastelloy C-276 resists HCl and 316L SS resists dilute sulphuric acid. The film continuously reforms after minor damage.
When abrasive particles strike the nozzle orifice at spray velocities (15–80 m/s), each particle impact locally removes the passive film at the impact point. Before the film can reform — a process that takes milliseconds — the fresh unpassivated metal surface is exposed to the corrosive liquid. The local corrosion rate at depassivated spots is 10–1,000 times the steady-state corrosion rate of the passivated surface.
Simultaneously, corrosion softens and weakens the grain boundaries at the metal surface, making the material more susceptible to particle abrasion at lower impact energies. The result: combined erosion-corrosion damage proceeds significantly faster than either mechanism alone would predict — sometimes by a factor of 3–10 over additive rates.
Specifying Hastelloy C-276 for HCl slurry service based on its excellent HCl corrosion resistance alone. Hastelloy C-276 has lower hardness than tungsten carbide or ceramics — in high-velocity abrasive slurry, its erosion rate may be unacceptably high despite its corrosion resistance. The correct selection combines the chemical resistance of Hastelloy with the wear resistance of a TC orifice insert.
- For corrosive slurry service: specify body material for chemical resistance; specify orifice insert material (TC, silicon carbide, or alumina) for abrasion resistance
- Reduce supply pressure where possible — erosion-corrosion damage rate scales approximately with velocity squared
- Inspect orifice diameter at shortened intervals in erosion-corrosion service — damage accumulation is non-linear; rapid degradation can occur with no warning after a slow initial period
- pH control of the slurry carrier liquid reduces the corrosive component — even modest pH increase from 2 to 4 dramatically slows acid attack at depassivated surfaces
The Four-Stage Degradation Sequence
Passive Film Formation
New or clean metal surface forms stable oxide passive film within seconds of exposure to the corrosive liquid. Corrosion rate is low — determined by ion diffusion through the film.
Particle Impact Depassivation
Abrasive particle strikes orifice edge or internal surface. Local impact energy exceeds the film's adhesion — film is removed at the impact zone over an area typically 5–50 µm².
Accelerated Corrosion at Bare Metal
Unpassivated metal dissolves at 10–1,000× the normal rate. The corrosion transient lasts until the passive film reforms — typically 1–100 ms depending on alloy and pH.
Corrosion-Enhanced Erosion
Acid attack along grain boundaries weakens the surface layer. Next particle impact removes material from a weakened substrate — erosion loss per impact increases as corrosion progresses.
When Standard Stainless Steel Is Not Enough
316L SS is the correct starting point for most industrial spray applications — it handles dilute acids, weak alkalis, and clean process water with long service life at modest cost. The alloys below are specified when 316L SS reaches the limits of its chemical resistance or when the combination of temperature, concentration, and fluid velocity produces unacceptable corrosion rates.
Hastelloy C-276
Ni-Mo-Cr alloy, UNS N10276The broadest-spectrum corrosion-resistant nickel alloy for spray nozzle service. The high molybdenum content (15–17%) provides resistance to pitting and crevice corrosion in chloride environments far beyond 316L SS; the chromium content (14.5–16.5%) provides oxidation resistance; and the combined alloy design resists both reducing acids (HCl, H₂SO₄) and moderately oxidising environments simultaneously.
Hastelloy C-276 is not suitable for strongly oxidising nitric acid (above ~65% HNO₃) or for hot concentrated sulphuric acid above 70%. In these environments, it is inferior to 316L SS. This counter-intuitive failure surprises engineers who assume C-276 is universally superior to stainless.
Tantalum
Pure metal, UNS R05200 / R05400Tantalum's corrosion resistance in mineral acids is unmatched by any common industrial alloy — it is essentially inert to all concentrations of sulphuric acid up to 175°C, hydrochloric acid up to boiling, and nitric acid in all concentrations including fuming HNO₃. The passive oxide film (Ta₂O₅) is extremely stable and does not dissolve in any of these media under normal conditions.
Tantalum is a specialist material for the most severe acid service. Its high density (16.6 g/cm³, twice that of steel), very high cost (20–60× stainless steel), and limited supply mean it is used only where no other metallic option performs adequately. For spray nozzle applications it is most commonly used as an orifice insert or a thin clad layer over a cheaper substrate rather than as a solid body.
Tantalum is rapidly and completely dissolved by: strong alkalis (NaOH, KOH) at any concentration; hydrofluoric acid at any concentration; fuming sulphuric acid (oleum); and fluoride-contaminated acids. In any of these media, Tantalum provides zero resistance — failure is catastrophic rather than gradual.
Alloy 20 (Carpenter 20)
Fe-Ni-Cr-Mo-Cu, UNS N08020Alloy 20 was specifically developed for sulphuric acid service — the copper content (3–4%) provides resistance to H₂SO₄ in the mid-concentration range (20–60%) where both 316L SS and standard Hastelloy alloys are marginal. The niobium stabilisation prevents sensitisation-driven intergranular corrosion in welded assemblies, making it suitable for fabricated nozzle headers and spray manifolds as well as individual nozzle bodies.
Titanium Grade 2
Commercially pure Ti, UNS R50400Titanium's corrosion resistance is driven by a very stable TiO₂ passive film — highly resistant to oxidising acids including dilute and moderately concentrated nitric acid, chromic acid, and wet chlorine. It is also highly resistant to seawater, dilute HCl at ambient temperature, and mildly reducing conditions where the pH remains above approximately 2.
The critical limitation is its sensitivity to reducing acids — dilute H₂SO₄ above 3%, concentrated HCl, and hydrofluoric acid all attack titanium rapidly. The TiO₂ passive film requires oxygen or an oxidising agent to maintain stability; in oxygen-depleted or strongly reducing environments, it dissolves.
Ceramic Orifice Inserts
Alumina (Al₂O₃), Silicon Carbide (SiC)Ceramic inserts address the erosion component of erosion-corrosion. Alumina (Al₂O₃) achieves Vickers hardness of 1,500–1,800 HV — more than 6× harder than tungsten carbide — providing exceptional abrasion resistance in high-velocity slurry service. Silicon carbide (SiC) reaches 2,500–2,800 HV and additionally resists most acids and alkalis that would attack metallic orifices.
The tradeoff is brittleness. Ceramics have low fracture toughness — they cannot tolerate impact loads (water hammer, pressure surges) or the thermal shock inherent in high-temperature quench service. The insert-to-body interface must be designed to accommodate differential thermal expansion; a ceramic insert in a metal body that undergoes thermal cycling will crack at the interface without adequate stress relief.
Ceramic inserts crack under rapid thermal cycling — avoid in quench nozzles that experience startup/shutdown temperature ramps. For high-temperature quench service, tungsten carbide inserts in an appropriate alloy body are the correct choice. Ceramics are suited to ambient-temperature abrasive slurry service where temperature is stable.
PTFE & PVDF
Polytetrafluoroethylene / Polyvinylidene fluoridePTFE has the broadest chemical resistance of any nozzle body material — it is inert to virtually all acids, alkalis, and solvents at temperatures up to approximately 260°C. The only exceptions are molten alkali metals, elemental fluorine, and chlorine trifluoride under extreme conditions not encountered in spray applications. For HF service where all metals fail, PTFE is the primary material.
PVDF (Kynar) is less chemically resistant than PTFE — attacked by fuming sulphuric acid, ketones, and some esters — but provides approximately 3–5× greater pressure rating and impact resistance at the same wall thickness, making it the preferred choice for moderate-pressure spray applications where PTFE's mechanical weakness would require impractically heavy-walled bodies.
O-Ring & Gasket Compatibility: The Often-Overlooked Failure Point
A nozzle body specified in Hastelloy C-276 for HCl service will still fail if the O-ring sealing the orifice insert to the body is Buna-N (NBR) rubber, which is rapidly attacked by acids. Seal material selection is a separate decision from body material selection — and seal failures are often the first failure mode in correctly-bodied nozzles installed in aggressive service.
Viton (FKM)
FluoroelastomerThe standard specification for chemical process and industrial spray service. Excellent resistance to acids, fuels, oils, and most solvents; good high-temperature performance to 200°C continuous. The correct default for most chemical plant nozzle applications.
EPDM
Ethylene Propylene Diene MonomerThe correct choice for alkaline environments, steam service, and hot water applications where Viton is inadequate. Very good resistance to caustic soda, sodium hypochlorite, phosphate solutions, and ketones.
PTFE (Encapsulated or Solid)
PolytetrafluoroethylenePTFE's chemical inertness makes it the universal seal material for aggressive chemistry that attacks elastomers — HF, concentrated oxidising acids, chlorinated solvents, and mixtures of incompatible chemicals. Encapsulated PTFE O-rings (PTFE over FKM or silicone core) combine PTFE's chemical resistance with an elastomeric core that maintains compression.
Kalrez (FFKM)
PerfluoroelastomerKalrez (DuPont) and equivalent perfluoroelastomers (Perlast, Simriz) combine PTFE-level chemical resistance with genuine elastomeric compression and recovery characteristics. Used when both extreme chemical resistance and reliable sealing under thermal cycling are required simultaneously.
Grafoil / Graphite Gaskets
Flexible GraphiteFor nozzle flange connections in high-temperature or high-pressure service where elastomeric O-rings cannot be used. Flexible graphite resists most chemicals at temperatures up to 500°C in non-oxidising environments and provides reliable sealing under flange bolt-load.
Selection Quick Reference
By Primary ServiceUse this as a first-pass guide — confirm with supplier data sheets for your specific chemical, concentration, and temperature combination before finalising.
NozzlePro Nozzles — Full Material Range
Every nozzle in NozzlePro's range can be specified in the body material and seal combination appropriate for your chemical service. Contact engineering with your fluid chemistry, concentration, temperature, and pressure for a specific material recommendation.
Your Fluid Chemistry Deserves a Specific Answer.
The decision matrix covers common scenarios. For mixed media, unusual concentrations, elevated temperatures, or erosion-corrosion service, contact NozzlePro engineering — we specify body material, orifice insert, and seal material together as a complete nozzle assembly for your application.