How to distinguish between 304 and 202 stainless steel pipes

I. What is 202 Stainless Steel Pipe 

202 is a standard designation in the US, replacing 1Cr18Ni9. The characteristic of austenitic stainless steel is that its transformation temperature is very high, so it can be used as a heat-resistant steel. 

For the austenitic stainless steel to undergo phase transformation, it must be heated above 1000℃. However, at 350℃, no change in the metal structure occurs, which means that the properties of the steel do not undergo fundamental changes. 

It will only expand due to heat, but the expansion is not significant and can be disregarded under normal circumstances. Therefore, 202 stainless steel has excellent high-temperature resistance properties. 

II. What is 304 Stainless Steel Pipe 

304 stainless steel is a common type of stainless steel material, with a density of 7.93 g/cm³. It is also known as 18/8 stainless steel, meaning it contains more than 18% chromium and more than 8% nickel. It can withstand temperatures up to 800℃ and has good processing properties and high toughness. 

III. Differences between 202 and 304 stainless steel 

01. The content of chemical substances is different. 

The content of nickel is about 4% and manganese is about 8% in 202, while the nickel content is about 8% in 304, and it contains more than 18% chromium. 

02. The application areas are different 

304 stainless steel is mainly used in food, storage and transportation, medical equipment, household items, automotive parts, plastic pipes, etc.

202 stainless steel is widely applied in architectural decoration, municipal engineering, highway guardrails, hotel facilities, shopping malls, glass handrails, public facilities, and other places. 

03. Different physical properties 

The tensile strength of 202 stainless steel σb (in MPa) is ≥ 520, and the condition yield strength σ0.2 (in MPa) is ≥ 275. 

The tensile strength σb (in MPa) of 304 stainless steel is ≥ 515 - 1035, and the condition yield strength σ0.2 (in MPa) is ≥ 205. 

04. Different corrosion resistance properties 

Because the chromium content in 304 stainless steel is higher than that in 202 stainless steel, its corrosion resistance is better. 

05. Price Difference Between the Two 

Due to the difference in nickel content, the cost of 202 is much lower than that of 304, resulting in the phenomenon where 202 is used to imitate 304 in the market. It should be noted that the 304 stainless steel in the 200 series is far inferior to the 300 series in terms of corrosion resistance and toughness. If incorrect purchase and use are made, serious safety issues will arise. 

IV. Methods for Distinguishing Between the Two 

Stainless steel reagents are used to detect the nickel content in steel and to distinguish which series of stainless steel it is. 

The rust resistance performance of different grades of stainless steel varies. This product distinguishes different types of stainless steel based on the rust resistance performance of the tested materials. The usage method is to drop a droplet of the test solution onto the surface of the material, and do not apply electricity first. 

For 202 stainless steel with a nickel content of about 4%, if the dripping area does not turn red within 10 seconds, then apply power for 5 seconds. After removing the battery, it will turn brick red in about 30 seconds. 

For 304 stainless steel with a nickel content of approximately 8%, if the dripped area does not turn red within 10 seconds, then apply power for 5 seconds. After removing the battery, it should remain unchanged for 15 minutes.