Analysis Of Five Mainstream Protective Tube Materials For Industrial Temperature Measurement – Precise Matching For Full-Range High-Temperature Protection

In metallurgy, chemical processing, power generation, and advanced materials manufacturing, the protective tube is the core component of a temperature sensor, directly determining measurement accuracy, equipment reliability, and service life. Currently, five mainstream materials cover the vast majority of industrial temperature measurement scenarios, providing standardized solutions for different temperature ranges and environmental conditions.

Based on industry technical parameters, the five materials – stainless steel 1Cr18Ni9Ti, superalloy GH3039, ceramics, silicon carbide, and refractory metals – have become the primary choices for protective tubes due to their stable performance and mature applications. Each material has a distinct role, complementing the others to form a complete protection system ranging from conventional temperatures to ultra‑high temperatures, and from ordinary atmospheres to severely corrosive environments.

1. 1Cr18Ni9Ti Stainless Steel Protective Tube (Basic Choice for Conventional Conditions)

As a general‑purpose base material, 1Cr18Ni9Ti stainless steel is the most widely used type, offering balanced properties, low cost, and well‑established processing technology. Its long‑term service temperature is 800 °C, with short‑term tolerance up to 900 °C. It is suitable for the vast majority of medium‑ and low‑temperature industrial applications, including ordinary kilns, HVAC equipment, and standard chemical production lines. However, it should be noted that in salt‑bath environments at around 850 °C, its service life is limited, and caution is required in high‑temperature corrosive atmospheres.

2. GH3039 Superalloy Protective Tube (Core Choice for Medium‑High Temperature Conditions)

GH3039 superalloy exhibits excellent oxidation resistance and hot strength, with minimal deformation or oxidation failure at elevated temperatures, and its thermal stability is significantly better than that of ordinary stainless steel. It is recommended for long‑term use at temperatures up to 850 °C, and can withstand short‑term exposure to 900‑1000 °C (depending on specific conditions). It is applied in high‑temperature kilns, heat‑treatment furnaces, and medium‑high temperature metallurgical lines, effectively filling the performance gap of stainless steel at higher temperatures.

3. Ceramic Protective Tube (For Ultra‑High Temperature and Severe Corrosion)

For operating conditions above 1300 °C with strong corrosion, alumina (corundum) ceramic tubes are the primary choice. Their long‑term service temperature reaches 1600 °C, and short‑term up to 1800 °C. They offer outstanding resistance to high temperatures and acid/alkali corrosion, making them suitable for measuring temperatures in high‑temperature corrosive media. The material has high hardness and withstands three thermal shock cycles from 1300 °C to room temperature without cracking, indicating some resistance to thermal shock. Nevertheless, due to its overall brittleness and limited impact strength, severe temperature fluctuations and mechanical impacts should still be avoided. Furthermore, this material is not applicable in atmospheres containing water vapor or in reducing atmospheres – selection must strictly match the operating environment.

4. Silicon Carbide Protective Tube (For Molten Metal and Abrasive High‑Temperature Conditions)

For measuring temperatures in molten metals and other high‑temperature, abrasive environments, silicon carbide offers distinct advantages. Its long‑term service temperature is 1600 °C, with short‑term capability up to 2000 °C (stable on air up to 1600‑1650 °C). Above 1200 °C, a protective SiO₂ oxide film forms on the surface, providing good oxidation resistance. The material combines excellent thermal conductivity and thermal shock resistance, resisting cracking under rapid temperature changes, while its high hardness and outstanding wear resistance enable it to withstand prolonged exposure to high‑velocity flows and molten media. It is the specialized tube choice for metallurgical molten‑metal temperature measurement and high‑temperature wear‑prone production lines.

5. Refractory Metal Protective Tube (For Extreme Ultra‑High Temperatures Above 1600 °C)

For extreme ultra‑high temperature conditions above 1600 °C in specific atmospheres, refractory metal tubes – made of molybdenum, tantalum, or tungsten – are the only viable solution. Molybdenum tubes can be used long‑term up to 1800 °C, with a maximum working temperature of 2300 °C; tungsten tubes up to 2500 °C; and tantalum tubes up to 2200 °C. These materials are exclusively suited for vacuum, inert, or reducing atmospheres at ultra‑high temperatures, where conventional materials fail. They meet the demands of advanced materials production, special metallurgy, and vacuum heat treatment. Critical limitation: molybdenum and tungsten are highly susceptible to oxidation in oxidizing atmospheres; they are strictly prohibited for use in air or oxygen‑containing environments. The furnace atmosphere must be carefully verified before selection.

Selection Summary Table

Accurate knowledge of each material's temperature limits, performance strengths, and applicable restrictions helps avoid selection errors that could lead to sensor damage or measurement inaccuracies. This significantly improves the stability and maintenance efficiency of industrial temperature measurement systems, providing reliable support for precise temperature control and safe production.