How do I test if my stainless steel is grade 304 or 316?

Generally speaking, it is not possible to determine the composition of a stainless steel by simple visual inspection, although colour can be a guide to separating austenitic grades (300 series) which have a yellow tinge, and ferritic grades (400 series) which have a blue metallic tinge).

So, how do you know what your sample is? Or how do you know that you are getting what you ordered?

First, you can ask the factory that produces stainless steel accessories to provide a test report showing the chemical composition.

Handheld Spectral Analyzer

As part of our quality control, in stainless steel fittings we use a handheld spectrometer to confirm composition. This instrument is a non-destructive tester with an alloy grade identification accuracy of 98.7%.

The handheld spectrometer enables us to test and identify our customers’ samples at the time of order. We can also provide a test certificate for your stainless steel fittings if required.

Other tests that can be used to identify the grade of stainless steel

For example, magnetic testing, spark testing and hardness testing can distinguish between certain grades of stainless steel. They cannot however, distinguish between 304 and 316 grades because both are non-magnetic, produce the same short, reddish sparks, and have similar hardness.

Acid testing is one test that will separate 304 and 316 grades of stainless steel.

Sulphuric acid strongly attacks 304 grade, producing green crystals and a dark surface, but its attack on 316 grade is slow and produces a brown surface

Hydrochloric acid attacks 304 grade very rapidly and produces gas, but attacks 316 grade only very slowly.

There are also proprietary test chemicals, such as Decapoli and Avesta 960 which detect the presence of molybdenum, a component of 316 grade, but not of 304 grade.