There are several reasons for this:
1. The first possibility is that the manufacturer uses stainless steel 201 to impersonate stainless steel 304 as an electric heating tube; stainless steel 201 material may cause rust due to the different nickel content.
2. If it is indeed stainless steel 304 material, it can be explained as follows:
Stainless steel does not rust under normal conditions. However, when it is exposed to chlorine or harsh environments, especially if the passivation layer on the surface is mechanically or chemically damaged, it is easier to rust than usual, so in this environment. It is easier to rust. The surface of the stainless steel products we usually use is passivated, and the thickness of the chrome oxide film on the surface is much thicker than that of the natural oxide film formed on the fresh surface. Therefore, the stainless steel heating tube will also rust. The stainless steel pipe is a steel pipe that does not produce rust in a weak corrosive environment such as the atmosphere or fresh water, and the chromium content in the steel must be ≥12%. If the chromium content is low or not in a weakly corrosive environment such as the atmosphere (including in a weakly corrosive environment such as the atmosphere, but under Cl-local rich enrichment conditions), rust will be produced. Acid-resistant steel pipes are steel pipes that are resistant to corrosion in strong corrosive media such as acid, alkali, salt, etc., but they are also resistant to corrosion under certain conditions, such as medium type, temperature, concentration, impurity content, flow rate, pressure, etc. There are no stainless steel pipes in the world that are not rusted or corroded under any conditions.