Stainless Steel Temperature And Colors

Stainless steel and its related superalloys are exceptional materials known for their resistance to rust, particularly when operating at room temperature or below. However, their resistance to oxidation diminishes when exposed to heat, although they still exhibit impressive resistance. This is why stainless steel and incoloy are preferred materials for the outer sheaths of our heater product lines.

When subjected to heat, the outer layer of our heaters’ material oxidizes as the iron combines with oxygen from the surrounding air. This oxidation process, commonly known as rust, can be advantageous. As stainless steel oxidizes, its surface changes color, providing a visual indication of the temperature it has reached.

Here’s a table illustrating the color changes stainless steel undergoes at various temperatures:

At around 500°F, a shiny stainless steel surface will retain some shine, but beyond this point, the colors become matte.

Chromium, present in all stainless steels and incoloy, plays a crucial role in preventing oxidation. The higher the chromium content, the lower the rate of oxidation. For example, 316 stainless steel, with a lower chromium percentage, oxidizes faster than incoloy, which has a higher concentration of chromium. The amount of nickel in the alloy also influences the adhesion of the oxide layer to the underlying metal.

Unfortunately, cyclic heating, characterized by repeated on-off cycles, can crack the protective oxide layer due to thermal expansion and contraction, exposing the underlying surface to additional oxidation. This emphasizes the importance of monitoring color changes in heaters to identify potential issues.

Different spots of discoloration on heaters indicate variations in temperature, which may result from obstructions or irregularities in the application setup. Understanding these color changes can help identify and address potential issues before they escalate.

In one notable case, a customer brought a cartridge heater with a black spot along its length, indicating localized overheating. Upon investigation, it was discovered that the black spot aligned perfectly with a screw hole in their sealing bar, resulting in insufficient metal around the heater. This incident underscores the importance of interpreting discoloration in stainless steels and related alloys to troubleshoot heating issues effectively.

In conclusion, the discoloration of stainless steels and their related alloys serves as a valuable diagnostic tool in identifying and resolving heating issues, providing crucial insights for maintaining optimal performance and efficiency in heating applications.