Structural Essence and Installation Mechanism Comparison
Fixed Flange Mounting Type: The probe end integrates a rigid metal flange (such as a slip-on/weld-neck flange), which is secured to the equipment's pre-set flange interface with bolts, allowing the probe to penetrate the medium. This forms a rigid, sealed, and non-adjustable insertion structure. The protective tube is typically made of 304/316L stainless steel or Inconel, suitable for high-pressure, high-temperature, and highly corrosive environments.
Surface Mount Gasket Type (i.e., Patch Thermocouple): The probe front end integrates a flexible thermal conductive gasket (such as metal foil, thermal conductive silicone, or ceramic-based composite gasket). The gasket is tightly attached to the surface of the object being measured through mechanical compression or screw fastening. This is a non-invasive, surface-contact type design that requires no drilling or welding, and the temperature sensing end directly measures the surface temperature.
Core Performance Parameter Comparison
Performance Dimension | Fixed Flange Mounting Type | Surface Mount Gasket Type (Patch Type) |
Mounting Method | Rigid flange bolt connection, requires pre-machined flange interface, penetrates into the medium | Thermal pad attached to the surface, fixed with screws or pressure plates, non-destructive installation |
Temperature Measurement Location | Inside the medium (steam, liquid, gas) | Outer surface of the equipment (pipes, rollers, barrels, molds) |
Temperature Range | 0℃ to 1300℃+ (S/B/K type) | 0℃ to 800℃ (limited by gasket material and insulation) |
Thermal Response Time | 60–90 seconds (long heat conduction path, large flange heat capacity) | ≤1–5 seconds (fast heat conduction of the gasket, low thermal resistance of the contact surface) |
Sealing Capability | High sealing performance, resistant to PN40+ pressure, compliant with ASME B31.1 | No sealing function, only heat transfer, not leak-proof, not pressure resistant |
Vibration Resistance | Very high (rigid connection) | Medium (gasket is prone to aging, long-term vibration may lead to loose contact) |
Maintenance Convenience | Disassembly requires shutdown, loosening multiple bolts, high replacement cost | Can be quickly replaced online, only requires removing the pressure plate or screws, no shutdown required |
Calibratability | Removable for inspection, supports separate calibration | Not removable, whole unit replacement for calibration, relies on manufacturer calibration |
Standard Basis | GB/T 30429-2013, GB/T 9119-2010 | No national mandatory standard, based on manufacturer's standards and IEC 60584-1 Internal Calibration |
Application Scenarios and Selection Logic
Fixed Flange Type:
Suitable for internal temperature measurement of high-pressure, high-temperature, and highly corrosive media: such as nuclear power main steam pipelines, hydrogenation reactors, refinery plant outlets, and large boiler flues;
Used for safety interlocks, mandatory calibration, and long-term continuous operation, requiring zero leakage and high reliability.
Gasket Type (Patch Type):
Specifically designed for surface temperature measurement where drilling and welding are prohibited and rapid response is required: such as injection molding machine nozzles, extruder barrels, lithium battery electrode rollers, heat treatment furnace rollers, metal mold surfaces, and reactor outer walls;
Suitable for process temperature difference analysis, equipment inspection, multi-point deployment, and temporary monitoring, requiring fast response, convenient installation, and non-destructive testing;
Product Examples: Kepson K-type patch thermocouple (response ≤2s), Omega WTJ-HD-72-S gasket type, thermal conductive silicone patch thermocouple (thickness 0.3–1mm).
Selection Mantra:
"To measure fluid inside the pipe, choose flange penetration; to quickly measure the outer wall, use a gasket patch."
Consequences of Incorrect Selection:
Using a gasket type for the inside of a high-pressure steam pipeline → The probe does not contact the medium, the reading lags, and temperature measurement fails;
Using a flange type for the outer wall of an injection molding machine nozzle → Requires damaging the equipment structure to open a flange port, doubling the cost and making maintenance impossible.
Installation and Operation Specifications
Fixed Flange Type:
Before installation, align the flange surfaces, ensuring parallelism ≤0.1mm/m;
Use a torque wrench to tighten the bolts diagonally and crosswise according to the standard torque (30–50 N·m);
Use metal spiral wound gaskets or graphite gaskets for sealing, rubber gaskets are prohibited;
After installation, perform an airtightness pressure test, with pressure ≥1.25 times the working pressure.
Gasket-type (Patch-type):
Thoroughly clean the surface to be measured, removing oil, oxide layers, and rust to ensure direct contact between the metal, gasket, and probe;
Attach the thermal conductive gasket (recommended thickness 0.3–0.8 mm) smoothly to the bottom surface of the probe, and then press it firmly against the surface to be measured;
Apply even pressure using screws or a pressure plate (recommended pressure 0.1–0.3 MPa), avoiding any gaps;
Do not use adhesives or sealing tape, as this will affect heat conduction;
Check the tightening status every 1–2 weeks to prevent poor contact due to thermal expansion and contraction;
The gasket will age and harden after prolonged use and needs to be replaced entirely; it cannot be repaired.
