Stainless Grade Selection: 304, 316L or Duplex for Vessels?
Selecting a stainless grade for a pressure vessel comes down to balancing four factors: the corrosion environment, the service temperature range, weldability in your workshop and total cost. For most vessel work the shortlist is 304/304L, 316/316L stainless plate and duplex stainless, and each occupies a distinct position on that four-way balance. This guide explains where each grade wins, and why austenitic grades dominate cryogenic applications.
The candidates in brief
304 and 304L
The workhorse austenitic grade, roughly 18 percent chromium and 8 percent nickel. It offers good general corrosion resistance, excellent formability and weldability, and the lowest price among the three. The L variant limits carbon to reduce sensitization risk in weld zones, which is why plate for welded vessels is normally ordered as 304L or dual-certified.
316 and 316L
Adding molybdenum, typically around 2 percent, gives 316 significantly better resistance to chlorides and many acidic media. 316L stainless plate is the default upgrade when the process fluid, cleaning chemicals or the plant environment, for example coastal or marine air, would pit 304. It costs more due to molybdenum and nickel content, and welds as comfortably as 304L.
Duplex stainless
Duplex grades combine austenitic and ferritic structure, delivering roughly twice the strength of the standard austenitics along with strong resistance to chloride pitting and stress corrosion cracking. The higher strength allows thinner walls for the same design pressure, which can offset the higher price per kilogram. The trade-offs: welding demands tighter control of heat input and interpass temperature, and duplex has a limited service temperature window, being unsuitable both for cryogenic use and for sustained high temperatures.
Working through the four factors
Corrosion environment
Start with the process medium and everything else the vessel will meet: cleaning agents, external atmosphere, insulation-related moisture. If chlorides are meaningfully present, move from 304L to 316L. If chlorides are high, temperatures moderate and stress corrosion cracking is a credible risk, duplex earns its premium. Specifying more corrosion resistance than the environment demands simply exports your budget to the nickel market.
Temperature range
Austenitic grades keep their toughness across an exceptionally wide range and remain ductile at deeply sub-zero temperatures. Duplex, by contrast, loses toughness in cold service and suffers embrittlement phenomena when held at elevated temperatures, so codes restrict its permissible range. For hot service near the upper limits, review grade-specific data rather than assuming.
Weldability and fabrication
304L and 316L are forgiving: standard procedures, wide parameter windows, predictable results. Duplex is weldable but unforgiving, requiring qualified procedures that preserve the austenite-ferrite balance in the weld zone. If your fabricator lacks duplex experience, the theoretical material savings can evaporate in trials and repairs.
Cost, calculated honestly
Compare total fabricated cost, not plate price per ton. Duplex's strength advantage can cut wall thickness enough to compete with 316L on material weight, but adds welding cost. 304L wins wherever the environment permits it. Run the comparison per project, since alloy surcharges shift the balance over time.
If you want plate options priced against a real specification, our team quotes all three families through the KAF Industries steel business group.
Why cryogenic vessels use austenitic grades
Cryogenic service is the clearest illustration of temperature-driven selection. Liquid nitrogen and oxygen temperatures reach far below the point where ferritic and duplex structures turn brittle. Austenitic stainless steels do not undergo a ductile-to-brittle transition, so grades like 304L retain impact toughness at cryogenic temperatures. That is why inner vessels of cryogenic tanks are almost universally austenitic stainless, a rule confirmed across the tank fleet our cryogenics team sells and services.
Certified material, whatever the grade
Grade selection only delivers its promise if the delivered plate truly is the grade ordered, which makes EN 10204 3.1 certification and heat traceability part of the decision. KAF Industries supplies hot rolled stainless plate in project-specific dimensions as the authorized Turkey representative of DKC Stainless, with mill-issued certificates for each order. Send your vessel specification through the steel business group or the contact page and we will quote grade options side by side. Right product. Right source. Right solution.
Frequently Asked Questions
When is 304L not enough for a pressure vessel?
Whenever chlorides, acidic media or aggressive cleaning regimes are present, or the vessel lives in coastal or chemically loaded air. Pitting and crevice corrosion in 304L show up around welds and gaskets first. In those environments 316L is the standard step up.
Is duplex stainless suitable for cryogenic tanks?
No. Duplex grades lose impact toughness at low temperatures and are code-restricted well above cryogenic range. Cryogenic inner vessels are built from austenitic grades, which stay tough at liquid gas temperatures.
Why order L grades instead of standard 304 or 316?
Low-carbon L variants resist sensitization, the carbide formation in weld heat-affected zones that invites intergranular corrosion. Since vessel fabrication is welding-intensive, L or dual-certified plate is the safe default at negligible extra cost.