Buyer Guide

Stainless Steel Grades 304, 316, 321, 904L: A Complete Comparison

By Ragnar Metals & Tubes Engineering Team • May 22, 2026 • 7 min read

Choosing the wrong stainless steel grade costs money — either through over-specification (buying 904L when 316L would last just as long) or under-specification (watching 304 fail in a coastal environment). This guide gives you the decision framework used by our export team to match material to application.

Grade 304 / 304L

Composition: 18% Cr, 8% Ni — the "18/8" stainless you see everywhere.

Key properties: Excellent general corrosion resistance; easy to weld; good formability; widely available at the lowest price point of any stainless grade.

Limitations: Susceptible to pitting and crevice corrosion in chloride environments (>200 ppm Cl⁻. 304L (low carbon, ≤0.03% C) is specified where welding is involved to prevent sensitisation.

Applications: Food and beverage equipment, kitchen appliances, architectural panels, water tanks, chemical containers for mild environments.

Grade 316 / 316L

Composition: 16% Cr, 10% Ni, 2% Mo — the molybdenum is the key difference from 304.

Key properties: The 2% Mo dramatically improves chloride pitting resistance (PREN ~24 vs ~18 for 304) and crevice corrosion resistance. 316L (≤0.03% C) is the standard for welded fabrication.

Limitations: Not suitable for hot seawater or environments above ~1000 ppm Cl⁻ at elevated temperatures. Not ideal where sensitisation from heat input is critical without post-weld annealing.

Applications: Offshore platforms (non-submerged), pharmaceutical and food processing, marine hardware, heat exchangers, chemical storage for moderate chlorides, the most widely exported stainless steel globally.

Grade 321

Composition: 18% Cr, 10% Ni + titanium stabiliser (Ti ≥ 5×%C)

Key properties: Titanium stabilisation prevents carbide precipitation (sensitisation) during exposure to temperatures of 400–900°C. This makes it the go-to grade for applications where post-weld heat treatment is impractical.

Limitations: Similar corrosion resistance to 304 — not designed for aggressive chloride environments. Slightly more expensive than 304/316L.

Applications: Exhaust manifolds, jet engine parts, heat exchanger shells in high-temperature service, furnace components, expansion joints, aircraft firewall fittings.

Grade 904L

Composition: 20% Cr, 25% Ni, 4.5% Mo, 1.5% Cu — a highly alloyed austenitic grade.

Key properties: Excellent resistance to reducing acids (sulphuric acid at all concentrations), phosphoric acid, acetic acid, and formic acid. PREN ~36 — better than 316L in chlorides. The copper addition specifically targets sulphuric acid resistance.

Limitations: Significantly more expensive than 316L (typically 3–4× the price per kg). Often over-specified when 316L or duplex 2205 would perform equally well.

Applications: Sulphuric acid plant piping, phosphoric acid production, seawater handling where duplex is not permitted, wet scrubbers, pulp and paper digesters.

Quick Comparison Table

Related pages: SS Pipe & Tube • SS Flanges • SS Fittings