Stainless Steel 316L

Materials ·

AISI 316L (UNS S31603) is a low-carbon austenitic stainless steel containing 16 to 18 percent chromium, 10 to 14 percent nickel, and 2 to 3 percent molybdenum, offering superior corrosion resistance to chlorides and many industrial chemicals, making it the most widely specified stainless grade for pump wetted-end components in food, pharmaceutical, chemical, and marine applications.

History

The 316 family of austenitic stainless steel was developed by Krupp-Thyssen Nirosta in Germany during the 1930s. The molybdenum addition was introduced specifically to combat pitting corrosion caused by chlorides, a critical problem in coastal and marine environments. The low-carbon L variant (0.03 percent max carbon) was introduced in the 1940s to prevent sensitization during welding — a phenomenon causing intergranular corrosion at grain boundaries. By the 1960s, 316L had become the standard material for pharmaceutical and food-grade pump wetted parts worldwide.

Key Properties

  • Density: 8.0 g/cm3
  • Tensile strength: 485 to 620 MPa
  • Yield strength: 170 MPa minimum per ASTM A276
  • Hardness: 95 HRB maximum in annealed condition
  • Excellent toughness maintained to cryogenic temperatures
  • Low magnetic permeability in annealed condition — non-magnetic for most practical purposes
  • Surface finish achievable: Ra 0.4 to 0.8 micrometres (food grade: Ra 0.8 maximum)

Corrosion and Chemical Resistance

  • Excellent resistance to chloride pitting up to approximately 1000 ppm Cl- at ambient temperature
  • Resistant to phosphoric acid, weak sulfuric acid, and many organic acids
  • Resistant to nitric acid in moderate concentrations at ambient temperature
  • Not suitable for concentrated sulfuric acid, hydrochloric acid, or hypochlorite solutions
  • Crevice corrosion risk in stagnant chloride solutions — specify fully penetrated welds
  • Pitting Resistance Equivalent Number (PREN) approximately 24 — limits use in concentrated seawater above 20 degrees C

Grades and Standards

  • ASTM A743/A744 CF-3M — cast equivalent of 316L for pump casings and impellers
  • ASTM A276 / ASTM A479 — wrought bar for pump shafts and machined components
  • EN 1.4404 — European designation for 316L wrought forms
  • EN 1.4409 — European cast equivalent (GX2CrNiMo19-11-2) for pump casings
  • ASME BPE standard for bioprocessing pump surface finish and material requirements
  • 3-A Sanitary Standard 75-03 for dairy and food contact pump components

Applications

  • Food and beverage processing (dairy, beer, juice, sauce) pump wetted parts
  • Pharmaceutical and biotech fluid transfer pump casings and impellers
  • Chemical process pumps handling dilute acids and caustic solutions
  • Marine cooling and bilge pump casings on ships and offshore platforms
  • Desalination pre-treatment pump components
  • Water feature and pool circulation pump casings

Advantages

  • Superior corrosion resistance compared to 304 SS in chloride-containing environments
  • Meets FDA, USDA, and 3-A sanitary standards for food contact surfaces
  • Non-contaminating — no metallic ions released into product flow
  • Readily weldable without post-weld heat treatment with the L grade
  • Full material traceability via EN 10204 3.1 mill test certificates
  • Electro-polishable to very low roughness values for cleanability in pharma service

Limitations

  • Not resistant to hydrochloric acid or wet chlorine at any concentration
  • Susceptible to stress corrosion cracking in hot chloride solutions above 60 degrees C
  • More expensive than 304 SS and significantly more costly than carbon steel
  • Work-hardens during machining — requires sharp tooling and controlled cutting parameters
  • Not suitable for concentrated sulfuric acid or strong reducing acid environments

Selection Criteria

  • Specify CF-3M cast or 316L wrought for all food, pharma, and marine pump wetted parts
  • Require EN 10204 3.1 mill test certificate for material traceability on all wetted components
  • Specify electropolish to Ra 0.8 micrometres for CIP/SIP pharmaceutical service
  • For seawater above 20 degrees C or above 5000 ppm chloride — upgrade to duplex or super-austenitic (904L or 254SMO)
  • Verify weld procedure qualification includes full penetration and post-weld passivation per ASTM A967

Top 10 Manufacturers

  • 1. Alfa Laval AB (Sweden) — ~14% of 316L pump market; sanitary and industrial centrifugal pump casings
  • 2. SPX Flow Inc. (USA) — ~10%; Waukesha and APV brand 316L hygienic pump components
  • 3. Grundfos A/S (Denmark) — ~9%; 316L impellers and casings for water and process pump applications
  • 4. IDEX Corporation (USA) — ~8%; Pulsafeeder and Viking brand 316L metering pump wetted parts
  • 5. Fristam Pumps USA — ~6%; 316L sanitary centrifugal and positive displacement pump components
  • 6. Xylem Inc. (USA) — ~6%; 316L stainless vertical turbine and submersible pump components
  • 7. Flowserve Corporation (USA) — ~6%; cast CF-3M process pump casings for chemical industry
  • 8. KSB SE (Germany) — ~5%; 316L chemical process and multistage pump casings
  • 9. Graco Inc. (USA) — ~5%; 316L fluid handling and diaphragm pump wetted-end components
  • 10. Verder Liquiflow (Netherlands) — ~4%; 316L peristaltic and gear pump wetted components