4. Materials and corrosion
Cast iron
| PT | EN | ES |
|---|---|---|
| Ferro fundido (cinzento) | Cast iron / Gray iron | Hierro fundido / Hierro gris |
Iron-carbon alloy with carbon as graphite flakes. Inexpensive, easy to cast, good vibration damping. Used for non-corrosive water service at moderate temperatures (< 100 °C) and pressures.
Gotcha: plain cast iron is not suitable for thermal-oil pumps (temperature) or fire-pump casings (pressure rating + impact resistance). Specify ductile iron or cast steel for those.
Ductile iron (nodular cast iron)
| PT | EN | ES |
|---|---|---|
| Ferro fundido nodular / Ferro dúctil | Ductile iron / Nodular cast iron | Hierro dúctil / Hierro fundido nodular |
Cast iron with magnesium addition that turns the graphite from flakes to spheroids. Roughly 3× tensile strength and substantially higher impact resistance than gray cast iron. Common upgrade material for casings exposed to thermal cycling or shock loading.
ASTM A536 is the typical grade designation; common types include 60-40-18 and 65-45-12.
Cast steel
| PT | EN | ES |
|---|---|---|
| Aço fundido | Cast steel | Acero fundido |
Carbon or low-alloy steel cast into pump casings. Used where pressure, temperature, or impact requirements exceed ductile iron. Standard grade for API 610 process pumps (typically WCB or WCC per ASTM A216).
Stainless steel — austenitic (300 series)
| PT | EN | ES |
|---|---|---|
| Aço inoxidável austenítico | Austenitic stainless steel | Acero inoxidable austenítico |
Iron-chromium-nickel alloys, typically 18% Cr / 8% Ni base (304) or with molybdenum addition for chloride resistance (316). Non-magnetic, ductile, good general corrosion resistance.
| Grade | Composition | Where used |
|---|---|---|
| 304 / 1.4301 | 18% Cr, 8% Ni | General mild service |
| 304L / 1.4307 | low-carbon variant | Welded fabrications |
| 316 / 1.4401 | + 2-3% Mo | Chloride-bearing fluids |
| 316L / 1.4404 | low-carbon | Welded chloride service |
| 321 / 1.4541 | + Ti stabilizer | High-temperature service (550-800 °C) |
Gotcha: 304 is not chloride-resistant. Sea water, brackish water, and chlorinated cooling water need 316 minimum, often duplex.
Duplex and super-duplex stainless
| PT | EN | ES |
|---|---|---|
| Aço inoxidável duplex / super-duplex | Duplex / super-duplex stainless steel | Acero inoxidable dúplex / súper dúplex |
Stainless steels with mixed austenite-ferrite microstructure. Roughly 2× yield strength of 316 and superior chloride / pitting resistance.
| Grade | PREN range | Where used |
|---|---|---|
| 2205 / 1.4462 | ~ 35 | Standard duplex; sea-water at moderate temperature |
| 2507 / 1.4410 | ~ 42 | Super-duplex; warm sea-water, brackish, sulfur-containing fluids |
PREN = Pitting Resistance Equivalent Number = %Cr + 3.3 × %Mo + 16 × %N. PREN > 40 is the typical super-duplex threshold.
Hastelloy
| PT | EN | ES |
|---|---|---|
| Hastelloy | Hastelloy | Hastelloy |
Family of nickel-based alloys (Haynes International trademark) for severe corrosive service. Common grades:
| Grade | Resistant to |
|---|---|
| Hastelloy B-3 | Concentrated hydrochloric acid |
| Hastelloy C-22 | Oxidizing chlorides, mixed acids |
| Hastelloy C-276 | Wet chlorine, hypochlorites, complex chlorinated solvents |
Cost is typically 8-15× the cost of 316 stainless. Used only where cheaper materials cannot survive.
CD4MCu (cast duplex)
| PT | EN | ES |
|---|---|---|
| CD4MCu | CD4MCu | CD4MCu |
ASTM A890 cast duplex stainless. Common in pump impellers and casings for pulp & paper, mining, and chemical service. Roughly equivalent corrosion resistance to wrought 2205 with the casting-friendly composition.
Bronze (gunmetal, naval bronze)
| PT | EN | ES |
|---|---|---|
| Bronze (canhão / náutico) | Bronze (gunmetal / naval) | Bronce (de cañón / naval) |
Copper-tin alloys, sometimes with zinc, lead, or nickel additions. Used for sea-water pump impellers (B62 gunmetal), marine fittings, and applications where the material must be non-sparking.
Gotcha: bronze is dezincified by some chloride-bearing waters, especially soft acidic waters. For hot or acidic sea-water service, specify duplex or higher-grade alloys.
Elastomers (O-rings and gaskets)
| PT | EN | ES |
|---|---|---|
| Elastômeros (anéis O-ring e juntas) | Elastomers (O-rings and gaskets) | Elastómeros (juntas tóricas y juntas) |
| Material | Temperature range | Resistant to | Avoid |
|---|---|---|---|
| NBR (Buna-N) | -30 to +100 °C | Petroleum oils, water | Polar solvents, ozone |
| EPDM | -40 to +150 °C | Hot water, steam, weak acids | Petroleum oils, fuels |
| FKM (Viton) | -20 to +200 °C | Most chemicals, oils, fuels | Hot amines, MEK, esters |
| FFKM (Kalrez) | -20 to +325 °C | Almost everything | Cost (10-30× FKM) |
| PTFE | -200 to +260 °C | Almost everything | Mechanical creep |
| Aflas | -10 to +230 °C | Amines, sour gas, acids | Cost |
Gotcha: “Viton” is a Chemours trademark for a specific FKM grade family. Generic FKM is the correct technical term. PT and ES catalogs use “Viton” loosely as a synonym for FKM, which can produce procurement mismatches between buyer and vendor.