Structural Essence and Physical Form
Fixed Flange Mounting Type: The probe end integrates a one-piece metal flange (such as a slip-on or weld-neck flange). It is rigidly connected to the equipment flange surface via bolts through the flange holes, forming a face-seal structure. The temperature sensing junction is located at the front end of the protective tube and directly inserted into the medium. The protective tube material is typically 304/316L stainless steel or Inconel, suitable for high-pressure, high-temperature fluid environments.
Spring-Loaded Thermocouple: The core structure features a built-in spring compression mechanism. The temperature sensing junction is embedded at the end of the protective tube. An elastic snap ring or compression spring ensures the probe is tightly pressed against the surface of the object being measured. There are no flanges or threaded connections. Installation only requires pressing the probe against the surface and locking the retaining clip. This is a non-invasive, surface-contact type design, often labeled as "spring-loaded," "snap-on," or "adjustable."
Core Performance Parameter Comparison
Performance Dimension | Fixed Flange Mounting Type | Spring-Loaded Thermocouple |
Mounting Method | Flange bolt tightening, requires centering and pre-machining of the flange interface, penetrating insertion into the medium | Spring elastic compression, no drilling required, conforms to the outer surface of the equipment, non-penetrating |
Temperature Measurement Location | Inside the medium (steam, liquid, gas) | Object surface (pipe outer wall, reactor shell, roller) |
Temperature Range | 0℃ to 1300℃+ (K-type, S-type, and B-type are all achievable) | ≤500℃ (most products are marked with an upper limit of 400–500℃, limited by spring material and insulation) |
Thermal Response Time | 60–90 seconds (long heat conduction path, large flange heat capacity) | ≤1 second (direct spring compression, extremely short heat conduction path) |
Sealing Capability | High sealing performance, can withstand pressures above PN40, complies with ASME B31.1 standard | No sealing function, only relies on contact heat transfer, not leak-proof, not pressure-resistant |
Vibration Resistance | Extremely high, rigid flange connection, strong impact resistance | Medium, long-term vibration may cause spring relaxation, requiring regular inspection of the tightening force |
Maintenance Convenience | Disassembly requires loosening all bolts, long downtime, often requires complete replacement | Can be quickly replaced online, only requires loosening the clamp, no downtime required |
Calibratability | Can be removed and sent for inspection, supports separate calibration | Not removable, requires complete replacement, calibration relies on replacing the entire unit |
Standard Basis | GB/T 30429-2013, GB/T 9119-2010 | No independent national standard, based on manufacturer's standards and IEC 60584-1 Calibration, a non-standard customized product |
Application Scenarios and Selection Logic
Fixed Flange Type:
Suitable for internal temperature measurement of high-pressure, large-diameter, and high-temperature media: such as petrochemical hydrogenation reactors, nuclear power main steam pipelines, refinery plant outlets, and large boiler flues;
Used for safety interlocks, continuous production, and mandatory calibration points, requiring long-term stability, high sealing, and corrosion resistance;
Typical industries: power, nuclear power, large-scale chemical industry, pharmaceutical CIP main pipelines.
Snap-ring Type:
Specifically for surface temperature measurement where drilling is not possible, welding is prohibited, and quick replacement is required: such as injection molding machine screws, extruder barrels, reactor outer walls, heat treatment furnace rollers, and lithium battery electrode sheet pressure rollers;
Suitable for equipment inspection, process temperature difference analysis, and temporary monitoring, requiring fast response, convenient installation, and non-destructive installation;
Product examples: Sanchang K-type spring-loaded (1s response), Tiankang snap-ring type (0–400℃), Jiangnan Best snap-on type (adjustable tightening), Changhui spring-loaded probe (0–600℃).
Selection Mantra:
"To measure fluid inside the pipe, choose flange penetration; to quickly measure the outer wall, use a snap-ring clamp."
Consequences of Incorrect Selection:
Using a snap-ring type for the inside of a high-pressure steam pipeline → The probe cannot contact the medium, the reading lags, and temperature measurement fails;
Using a flange type for the outer wall of an injection molding machine screw → Requires additional processing of the flange interface, damaging the equipment structure, and doubling the cost.
Installation and Operation Specifications
Fixed Flange Type:
Align the flange surface before installation, parallelism ≤0.1mm/m;
Use a torque wrench to tighten the bolts diagonally according to the standard torque (30–50 N·m);
Use metal spiral wound gaskets or graphite gaskets for sealing, rubber is prohibited;
Perform airtightness pressure testing after installation, pressure ≥1.25 times the working pressure.
Spring-clip type:
Clean the surface to be measured, removing oil and oxide layers to ensure direct metal-to-metal contact;
Attach the probe to the surface and tighten the locking collar to create a stable clamping force from the spring (recommended clamping force 5–10 N);
The use of PTFE tape or adhesives is prohibited, as they affect heat conduction;
Check the spring clamping condition every two weeks to prevent poor contact due to thermal expansion and contraction;
After long-term use, the spring will fatigue and require complete replacement; it cannot be repaired.
Industry standards basis:
Fixed flange type: Strictly follows GB/T 30429-2013 "Industrial Thermocouples" and GB/T 9119-2010 "Steel Pipe Flanges with Flat and Raised Faces";
Spring-clip type: There are no mandatory national standards. Its structure and performance are internally calibrated by the manufacturer based on IEC 60584-1 (Thermocouple calibration tables) and IEC 60584-2 (Tolerances). Product parameters are subject to the manufacturer's technical specifications.
Industry Application Tips
In the injection molding industry, spring-loaded thermocouples are the only practical solution for closed-loop temperature control of the screw, as drilling or welding is prohibited due to the high-speed rotation of the screw. Spring-loaded thermocouples enable non-destructive, fast, and highly responsive temperature measurement;
In the main cooling circuit of nuclear power plants, fixed flange-type thermocouples are the only compliant installation method, as they must meet the high-pressure sealing and seismic requirements of ASME B31.1. Spring-loaded thermocouples are strictly prohibited;
In the hot pressing process of lithium battery electrodes, spring-loaded thermocouples are used for monitoring the surface temperature of metal rollers, requiring high fitting accuracy and fast response (≤1s) to meet the process temperature control requirement of ±1℃;
In the temperature distribution monitoring of the outer wall of chemical reactors, spring-loaded thermocouples enable multi-point non-destructive deployment, while flange-type thermocouples are only used for penetration temperature measurement at critical points, forming a redundant system.
