What is a fixed flange-mounted probe-type thermocouple

Fixed flange-mounted probe-type thermocouples offer the core advantages of high pressure resistance, strong vibration resistance, and easy maintenance, making them an indispensable temperature sensing solution in industrial scenarios involving high pressure, large diameters, and corrosive media. Their standardized interface and modular design make them one of the most reliable and safest temperature measurement interface types in modern process industry automation systems.

Structure and Sealing Mechanism

The fixed flange-mounted probe-type thermocouple consists of four parts: the thermocouple element, magnesium oxide insulation layer, protective tube, and flange connection. The thermocouple element uses K-type (nickel-chromium/nickel-silicon) or E-type (nickel-chromium/copper-nickel) alloy wires, welded to form the temperature measuring junction; the insulation layer is made of high-purity magnesium oxide powder, ensuring electrical isolation and balanced heat conduction; the protective tube material is selected according to working conditions, using 316L stainless steel (corrosion-resistant), Inconel 600/625 (high-temperature oxidation resistant), or corundum ceramic (ultra-high temperature insulation); the flange connection is a butt-welded or slip-on steel flange, conforming to ASME B16.5 and JB/T 8622 standards. The flange sealing surface is mostly a raised face (MF) or tongue and groove face (TG), requiring precise matching with the corresponding gasket to achieve high-pressure sealing.

Sealing Materials and Pressure Adaptability

Flange sealing relies on metal-wound gaskets (316L stainless steel strip + flexible graphite) or flexible graphite gaskets, which can withstand working pressures of 10–25 MPa and high-temperature environments of 800–1300°C. In corrosive media (such as chloride ions, acidic steam), PTFE-coated gaskets can be used to avoid metal ion contamination. The sealing surface must be thoroughly cleaned before installation, free of carbon black, oil stains, radial scratches, or pits, to ensure uniform pressure on the gasket and prevent interface leakage.

Core Application Scenarios

Petrochemical Industry: Catalytic cracking reactors, high-pressure pipelines in hydrogenation units, distillation column top temperature control

Power Industry: Boiler superheaters, reheaters, main steam pipelines

Metallurgical Industry: Electric arc furnace walls, continuous casting crystallizer cooling water systems

Nuclear Energy Systems: Primary circuit coolant temperature monitoring (requires high-purity Inconel material)

Pharmaceutical and Food Industries: Sanitary flange thermocouples (mirror polished, no dead-angle design) meeting GMP standards

Calibration and Lifespan Management

Calibration Cycle: 12 months under normal operating conditions; 6 months for high-temperature cycling (>600℃) or corrosive environments

Calibration Method: Comparison method, placed in a tubular calibration furnace (±0.2℃/min stability) together with an S-type standard thermocouple, recording the thermoelectric potential at 300℃, 600℃, and 900℃. Error ≤ ±1.5℃ (K-type Class III)

Lifespan Evaluation Indicators: Thermoelectric potential drift rate (≤5μV/year), insulation resistance (≥100MΩ@500VDC), protective tube oxidation thickness (≤0.1mm/year)

Typical Lifespan: 5–8 years in medium and low-temperature environments; 2–4 years in high-temperature cycling (>800℃)

Installation Specifications and Operating Procedures