How to distinguish between 304 and 316 materials

304 and 316 pipe fittings both belong to austenitic stainless steel, with the core difference lying in their chemical composition: 316 fittings contain 2%-3% molybdenum (Mo) and a higher nickel content (10%-14%), while 304 fittings have no molybdenum and a nickel content of 8%-10.5%. This compositional difference leads to significant variations in corrosion resistance and application scenarios, and they can be distinguished through the following practical methods:​

Firstly, checking markings and certification documents is the most direct and reliable way. Regular fittings will be stamped on the surface or labeled with "304", "SUS304" (corresponding to Chinese standard 06Cr19Ni10) or "316", "SUS316" (corresponding to Chinese standard 06Cr17Ni12Mo2). Meanwhile, you can request a Material Test Certificate (MTC) from the supplier, which will clearly indicate the molybdenum content for 316 fittings. Be wary of products only marked "stainless steel" or "food-grade stainless steel" without specific model numbers, as they may be inferior substitutes.​

Secondly, simple tests can be used for auxiliary judgment. When 吸附 ing the fitting surface with a strong magnet (such as a neodymium magnet), both should show weak or no magnetism (weak magnetism may occur after processing, and 316 has even weaker magnetism). A strong magnetic reaction indicates the product is likely not 304/316 (possibly 201 or 430 stainless steel). In professional scenarios, molybdenum test kits can be used: apply the test solution to a cleaned fitting surface—316 will show a specific color reaction (e.g., red) due to molybdenum content, while 304 will have no obvious change. For precise detection, a handheld XRF analyzer can directly read the molybdenum content data.​

In addition, appearance, weight, and application scenarios can serve as supplementary references. Both have a silver-white luster, but 316 has a finer surface. Due to its slightly higher density (7.98g/cm³ vs. 304’s 7.93g/cm³), 316 feels heavier at the same volume (the difference requires accurate weighing). 304 fittings are suitable for non-corrosive environments such as inland household water supply and general food processing. 316, with 3-5 times stronger chloride corrosion resistance, is commonly used in coastal buildings, chemical pipelines, medical equipment, etc. The material can be inferred from the application environment. In terms of price, 316 fittings are 30%-50% more expensive than 304 due to the higher cost of molybdenum, so unusually low quotes should be carefully verified.