Stainless Grade Selector — Chloride, Temperature and pH

Chloride content, service temperature and pH decide which stainless grade will survive — not price. Enter the three numbers and the selector names the grade, the alternatives, and the reason each one applies.

What the selector asks for

• Chloride content in ppm (seawater is about 19,000 ppm)
• Service temperature in °C
• pH of the medium
• Plate thickness
• Whether the equipment is welded and left as-welded
• Sour service (H2S), reducing acid, hygienic contact or nickel-free constraints

How the recommendation is reached

Pitting and crevice risk are ranked with PREN (%Cr + 3.3 x %Mo + 16 x %N), which is why 304L at PREN 19 and 316L at PREN 25 give way to duplex 2205 at 35 and super duplex 2507 or 254 SMO above 42 as chlorides and temperature climb.

Chloride stress corrosion cracking is treated separately: it needs tensile stress, chlorides and roughly 60 °C together, and it rules standard austenitic grades out rather than merely down — which is the most common reason a specification moves off 316L. Ferritic 444 and the duplex family resist it.

Above about 525 °C the question becomes creep strength and carbide stability, so the selector moves to stabilised 321 and 347, 304H, or heat resistant 309S and 310S. In reducing acids it moves to 904L, 254 SMO or Alloy 20, where molybdenum and copper, not chromium, do the work.

Grades it selects from

304L, 316L, 317L, 321, 347, 304H, 309S, 310S, 904L, 254 SMO, Alloy 20, duplex 2205 and 2304, super duplex 2507 and S32760, and ferritic 430, 439 and 444.

Before you order

The selector is a shortlisting aid, not a material certificate. PREN ranks grades against each other; it does not predict a service life. Send the full process analysis, design code and welding route to Stancor Stainless and our technical team will confirm the grade, thickness and certification scope.

For availability, mill test certificates and a quotation, contact Stancor Stainless.