How to Verify 304 Stainless Steel Sinks Before You Ship

Every importer eventually faces the same question: is the sink in the carton actually 304, or is it 201 with a 304 quotation? The price gap between the two grades is large enough to tempt a supplier, and once the container has sailed, proving the difference becomes much harder. These are the checks that actually work, in the order you should apply them.

Start with documents, not opinions

Ask for the mill test report or material certificate for the coil or sheet used in your order, not just a generic certificate of conformity. A proper report states the grade, the heat number and the chemical composition, including the nickel content that distinguishes 304 from 201. Then keep the document: if a dispute arises later, the heat number lets you trace the actual coil rather than argue about a photograph.

Checks you can do with a sample

• Thickness. Measure with a micrometer at several points on the bowl wall and base, not just at the rim where the material is thickest. Quoted thickness is often the nominal sheet, while the finished bowl is thinner after drawing.
• Weight. Weigh a single sink and compare it against the weight the factory quoted. Stainless steel density is fixed, so a lighter sink with identical dimensions is either thinner or a different grade.
• Edges and welds. Burrs, uneven polishing and porosity at the drain weld are the first visible signs of a supplier cutting corners, and they tend to travel with material substitution.
• Finish behaviour. A 201 bowl usually looks brighter and more reflective when new, while 304 has a deeper, softer tone. This is a hint, not proof.

The magnet test - useful, but misunderstood

Many buyers are told that a magnet will identify 201 because 201 is magnetic and 304 is not. In practice, 304 becomes slightly magnetic after deep drawing and forming, so a magnet alone will mislead you. Use it only as a supporting observation, never as the deciding test.

Instrument and laboratory checks

If the order value justifies it, an X-ray fluorescence (XRF) analyser gives a direct reading of chromium and nickel content on the finished sink and takes seconds per piece. Failing that, arrange a laboratory analysis of a sample from the production batch. Salt spray testing per ASTM B117 is useful for the finish and coating, but it tests corrosion behaviour rather than confirming the grade.

The commercial sanity check

Compare the quotation against the market. If a price is comfortably below what several other factories quote for a 304 sink of the same thickness, the difference is usually material, not efficiency. Ask the supplier directly which grade the offer covers, and put the answer in writing.

What to write into the purchase order

• Grade: 304 stainless steel, with mill test report required for each batch.
• Nominal thickness and the tolerance you will accept on the finished bowl.
• Weight per piece, and the right to reject on a weight deviation above an agreed percentage.
• Sampling and inspection terms, including who pays for a failed laboratory test.

This is the practical side of a question we cover from the cost angle in 304 vs 201 stainless steel sinks. If you want to compare production directly, the handmade range and the pressed range both list the material used, and TEGAO can supply material certificates with any quotation through the contact page.