To check whether a material is stainless steel grade 202 or grade 304, you can use several methods. Keep in mind that these methods may require the use of specialized equipment and are typically performed by professionals. Here are some common ways to distinguish between SS 202 and SS 304:

1. Chemical Composition Analysis:
   Stainless steel grades are differentiated based on their chemical composition. You can perform a chemical composition analysis using techniques such as X-ray fluorescence (XRF) or optical emission spectroscopy (OES). These methods can determine the percentage of elements in the stainless steel, allowing you to identify the specific grade.
2. Spark Testing:
   Spark testing is a traditional method used by experienced professionals to identify stainless steel grades. It involves using a grinder or abrasive wheel to create sparks on the surface of the material. The sparks produced by SS 202 and SS 304 will have different patterns, allowing experts to distinguish between the two grades based on their appearance.
3. Magnetic Test:
   SS 202 is a type of austenitic stainless steel, which is non-magnetic. On the other hand, SS 304 is also austenitic but can exhibit a weak magnetic response due to the presence of some ferrite in its microstructure. You can use a simple magnet to check for magnetic properties. If the material is non-magnetic, it is likely SS 202, whereas a weak magnetic attraction might indicate SS 304.
4. Microstructure Examination:
   Under a microscope, the microstructure of stainless steel grades can show distinct features that differentiate them. However, this method requires sample preparation and access to a metallurgical laboratory.
5. Density Measurement:
   Stainless steel grades have different densities. You can measure the density of the material using various techniques to provide clues about its grade.

It’s essential to note that accurately identifying stainless steel grades can be challenging, and some methods may require specialized equipment and expertise. If you need to determine the grade for a specific application or quality assurance purposes, it’s best to consult with a material testing laboratory or a professional metallurgist.

Please remember that handling stainless steel requires caution to prevent injury, and you should use appropriate safety equipment when conducting tests involving grinding or chemical analysis.