304 vs SUS316: 20% price difference, which one is more suitable for your project?

304 vs SUS316 stainless steel: 20% price difference, how should buyers choose?

In-depth analysis from the perspectives of chemical composition, corrosion resistance, high temperature resistance, and cost performance!

304 vs SUS316 stainless steel chemical composition：

304 vs SUS316 Corrosion resistance:
Neutral environment (air/tap water): Both perform well, 304 is sufficient to meet daily needs.
Chloride ion environment (seawater/salt water/swimming pool water):
304: pitting begins to appear after 200 hours, and local rust occurs after 1 year;
SUS316: no obvious corrosion after 1000 hours, and the surface remains smooth for more than 3 years (measured data source: NACE TM0177 standard).
Acid and alkali environment (such as 10% sulfuric acid/hydrochloric acid):
304: can only withstand 24 hours at 20℃;
SUS316: can persist for more than 72 hours under the same conditions, and the corrosion resistance is increased by 50% when the concentration is ≤5%.

304 vs SUS316 High temperature resistance:
Room temperature to 500℃: The strength of the two is similar, and 304 is more cost-effective;
500-800℃: 304 begins to show obvious oxide scale, and the oxidation rate of SUS316 is reduced by 40%;
Above 800℃: 304 grains coarsen rapidly, and SUS316 can withstand short-term high temperatures of 1200℃ (such as boiler superheater scenarios).

304 vs SUS316 Mechanical properties:
Tensile strength: ≥515MPa, meeting most structural requirements;
Welding performance: 304 welding does not require special treatment, SUS316 requires molybdenum-containing welding wire (such as ER316L), and solid solution treatment is recommended after welding;
Cold processing performance: 304 is easier to form, and SUS316 needs to control the deformation of ≤15% during cold bending to prevent cracks.

304 vs SUS316 Cost cycle: 
Purchase cost: SUS316 is 20%-30% more expensive than 304 (taking Φ57×3mm pipe as an example, the price difference is about 15-20 yuan per meter);
Maintenance cost: In marine engineering, 304 pipelines require anti-corrosion coating maintenance every year (the cost accounts for 10% of the purchase price), while SUS316 can be maintenance-free for 5 years;
Replacement cost: The average life of 304 in chemical equipment is 2-3 years, while SUS316 can reach 5-8 years, and the full-cycle cost is reduced by 40%.

 

Purchasing pitfall avoidance guide: 3 details determine long-term benefits
Look at the implementation standard: 304 needs to confirm whether it is GB/T 24511-2017 (new national standard) or ASTM A240 304 to avoid low-priced and inferior products (nickel content less than 6%);
SUS316 needs to verify whether the molybdenum content is ≥2% (some manufacturers use 316L to impersonate, and the molybdenum content is only 1.8%).
Surface treatment requirements:
For food-grade scenes, choose BA-level polishing (roughness Ra≤0.8μm), and for chemical scenes, choose pickling and passivation (remove welding oxide scale).
Quality assurance documents are necessary:
Material certificate (must include C, Cr, Ni, Mo element content);
Intergranular corrosion test report (ASTM A262 method E, SUS316 must pass).