How to Select Temperature Sensor Sleeves Made of Stainless Steel, Ceramic, or Glass
Many engineers select casing materials based solely on price. While stainless steel is suitable for general operating conditions, when exposed to high-temperature furnaces, seawater salt mist, or strong acids and bases, inexpensive stainless steel pipes can suffer from oxidation and failure within just a few months. Conversely, installing brittle ceramic pipes in vibration-prone pipelines can lead to sudden fractures upon minor impact. A more insidious case involves chloride-containing media: a 304 stainless steel pipe may appear intact externally, yet internal pitting corrosion can propagate from the inner wall outward; once the corrosive medium penetrates, the entire sensor assembly may be rendered unusable. One ceramic manufacturer previously used K-type thermocouples with stainless steel protective tubes in a shuttle furnace operating at 1,200 °C, requiring replacements every two months on average; after switching to silicon carbide ceramic tubes, the service life extended to ten months, and annual replacement costs were reduced by 75%—the selection of casing materials is therefore not merely a one-time cost decision, but a critical factor in sustaining long-term process competitiveness.
Comparison of Key Parameters for Three Types of Casing
| Comparison Dimensions | Stainless steel 304/316L | Ceramics (alumina/corundum) | vycor |
|---|---|---|---|
| Temperature range | -200~800℃ | 0~1600℃ | ≤1700℃ |
| corrosion resistance | 316L chloride ion resistant | Resistant to strong acids, strong bases, and molten salts | Resistant to acids but not to bases; high purity |
| mechanical strength | High, impact-resistant | Prone to breakage; avoid impact and bumps. | Poor condition; fear of impact |
| thermal shock resistance | Excellent | Defective; prone to cracking upon rapid cooling or heating. | same as |
| Typical scenarios | Chemical piping, water treatment, food and pharmaceuticals | High-temperature furnaces, glass melting furnaces, molten steel temperature measurement | Semiconductors, Photovoltaics, Laboratories |
| prime cost | low | Middle | Medium to high |
3 Key Considerations for Model Selection
Key Point 1: Set the upper temperature limit
The temperature resistance of the liner must cover the peak operating temperature of the process, with an appropriate safety margin. For temperatures up to 800 °C, stainless steel is the most cost-effective option; above 800 °C, conventional stainless steel oxidizes rapidly, necessitating replacement with 310S stainless steel or high-temperature alloys; above 1300 °C, only high-alumina ceramics, corundum tubes, or quartz glass are viable options.
Key Point 2: Determining the Material of the Medium
For environments containing chloride ions (seawater, brine), 316L stainless steel is the preferred choice; using 304 stainless steel may lead to pitting corrosion and perforation. For strong acids or strong bases, ceramic or PTFE linings are recommended; for high-purity environments such as semiconductor or vacuum metallurgy processes, quartz glass should be selected to avoid metal contamination.
Key Point 3: Determine the structure based on operating conditions
For high-pressure, high-velocity fluid applications, use thick-walled or conical tubes to prevent fracture; in vibration-prone environments, exercise caution when using ceramics, and consider employing a metal-ceramic composite structure; the recommended insertion depth is 10–15 times the pipe diameter, and filling with magnesium oxide powder can accelerate response time.
Common Pitfalls Warning
- Avoid rigid installation of ceramic pipes—due to their high brittleness, both transportation and installation require cushioning and protective measures;
- Do not rely on 304 stainless steel for chloride-containing service conditions—pitting corrosion can propagate from the interior toward the exterior, causing perforation; the material may still appear intact, but it has already failed.
- Do not overlook sealing—insufficient sealing of the negative-pressure pipeline may allow cold air to be drawn in, leading to underestimation of the temperature measurement.