A temperature gauge is a local indicating thermometer (mechanical or expansion type) that shows process temperature without external power. In oil & gas it’s used on heat exchangers, reactors, furnace coils, steam tracing circuits, lube oil skids, and utility headers for commissioning checks and operator rounds.

• Main types: bimetal, gas-actuated (bulb & capillary), liquid-in-glass/expansion.
• Units: °C/°F (single or dual scale).

• Bimetal: a spiral/helix made of two metals with different thermal expansion twists with temperature; motion drives the pointer.
• Gas-actuated: a bulb filled with inert gas is connected via capillary to a measuring element (Bourdon/diaphragm). Gas pressure changes with temperature and moves the pointer; supports remote mounting.

Pros/Cons: Bimetal = simple, fast response, short stem; Gas-actuated = remote readout, wide range, compensates ambient with built-in bimetal/compensation mechanism.

• Bimetal: local indication, short insertion, moderate vibration, cost sensitive, −50…+500 °C typical.
• Gas-actuated: need remote dial (up to tens of meters), larger bulbs, ambient-compensated capillaries, wider ranges including cryogenic/high temp (check datasheet).
• For very low temps or extreme ambient swings, gas-actuated often performs better.

• A thermowell is a protective, pressure-retaining sheath that isolates the sensing element from the process, allowing removal without depressurization.
• Improves mechanical strength, corrosion/erosion resistance, and serviceability.
• Common shank styles: tapered, stepped, straight; process connections: threaded, flanged, weld-in, and sanitary.

• ASME PTC 19.3 TW-2016: thermowell design & wake frequency calculations (strength, static, and fatigue).
• EN 13190 / ASME B40.200: performance/accuracy and construction requirements for dial thermometers (bimetal, gas-actuated).
• Project specs often add material, hydrotest, PMI, and PWHT requirements for wells.

• Place normal operating temp in the middle third of the scale for readability.
• Avoid running within the last 10% of range; consider upset/start-up conditions.
• For cryogenic or very hot service, confirm ambient effects and case rating; gas-actuated may be preferable.

• Typical classes (per common industry practice and EN/ASME styles): ±1.0%, ±1.5/1.6%, ±2.0% of full scale.
• Higher-grade “test” thermometers exist; verify conditions of test and reference standard on the datasheet (EN 13190 / ASME B40.200).

• Rule-of-thumb for bimetal/gas-actuated bulbs: immerse at least the sensitive length (bulb length) and target ≥ 10× stem diameter into the flow.
• For pipelines: the tip should reach near the centerline (or ≥ 1/3 of ID) to reduce wall conduction error.
• Avoid the tip touching the inner wall; maintain clearance to prevent vibration damage.

Wake frequency is the vortex shedding frequency created by fluid flow past the well. If it approaches the well’s natural frequency, resonance can cause fatigue failure.

• Verify with ASME PTC 19.3 TW-2016 calculations (stress, frequency ratio, Strouhal number).
• Mitigations: shorter insertion, tapered/stepped shank, stiffer material, support collar, or change location/velocity.

• Bimetal: generally faster for short stems due to direct metal contact; improves with spring-loaded tips and heat transfer paste.
• Gas-actuated: depends on bulb size, capillary volume, and ambient compensation; larger bulbs can be slower but stable.
• Stepped/tapered thermowells improve response vs straight wells.

• Dial sizes: 100–160 mm (4–6") for process plants; larger improves readability and graduation spacing.
• Entry: bottom, back, or every-angle adjustable heads to orient the dial.
• Windows: glass, laminated safety glass, polycarbonate (impact-resistant; mind UV/solvents).

• Case temperature shifts zero/span; use models with specified ambient range and ambient compensation for gas-actuated systems.
• Direct sun causes case pressure rise and window bulge; vented/sealed designs address this.
• Protect capillaries from kinking and temperature extremes; route away from hot surfaces and provide guards.

• Connections: 1/2" or 3/4" NPT/BSPT threaded, RF flanges, weld-in; sanitary tri-clamp for hygienic service.
• Materials: 316/316L SS (general), Monel/Hastelloy/Alloy 600/625 for chlorides, H₂S, or high temp; verify ISO 15156/NACE for sour service.

• Use a lagging extension on the thermowell/thermometer to clear insulation thickness.
• Specify U-dimension (insertion) plus T-dimension (from process to head) in datasheets.
• Seal insulation to prevent water ingress and corrosion under insulation (CUI).

• Prefer a single primary unit (°C) with optional secondary (°F) as smaller scale.
• Use clear major/minor graduations; avoid clutter; include tag number.
• Optional limit markers or red zones for alarm/operating limits.

1. Use a dry-block calibrator or liquid bath with a traceable reference thermometer.
2. Immerse the bulb/stem to the specified depth; allow to stabilize.
3. Check at 5 points (e.g., 0, 25, 50, 75, 100% of span) up and down; record as-found / as-left.
4. For ice/boiling checks: use 0 °C ice bath and local boiling point (altitude corrected).

• Heat conducted from process to ambient along the stem causes the sensed temperature to bias toward ambient.
• Mitigate with sufficient immersion, spring-loaded bulbs, heat transfer grease, and tapered/stepped wells.
• Insulate exposed well/stem sections where appropriate.

• Vibration can cause pointer flutter and wear; use liquid-filled cases, remote mounting (gas-actuated), or relocate.
• Thermowell resonance risks fatigue; perform wake frequency checks and shorten/stiffen the design if needed.

• Armored stainless capillary in lengths typically up to 25–30 m (check vendor limits).
• Specify length, armor type, ambient compensation, minimum bend radius, and routing method.
• Provide dial mounting (surface, panel, pipe mount) and orientation details.

• 316/316L for many hydrocarbons/steam; upgrade to Monel/Hastelloy/Alloy 625/600 for chlorides, H₂S, or high temperature oxidation.
• Confirm ISO 15156/NACE MR0175 for H₂S service; consider cladding/coatings if needed.
• Account for erosion (two-phase flow) and galvanic effects in dissimilar metal systems.

• Too little immersion → extend well or relocate to elbow/thermowell tee.
• Tip touching pipe wall → re-align and verify clearance.
• Wrong angle for readability → use adjustable-angle heads.
• Capillary kinks → use proper guards, radius, and routing.

• Use a tapered or stepped thermowell (if stress checks pass).
• Spring-load the bulb against the well tip; add heat transfer paste.
• Shorten insertion just enough to pass wake frequency while keeping adequate immersion.

• Dial gauge: simple, no power, quick local check, good for non-critical loops.
• Transmitter (RTD/TC): required for control, remote monitoring, alarm/trip, historian, and custody/safety interlocks.
• Many plants install both: gauge for operators + transmitter for control.

• Choose IP65/IP66 or equivalent NEMA for washdown/outdoor; consider UV-resistant windows.
• Liquid-filled cases help with vibration; verify temperature range of the fill (e.g., silicone for wide ambient).

• Range, dial size, mounting, bulb dimensions (length/diameter), capillary length and armor.
• Ambient compensation method, case rating, window, and pointer features (max/min markers).
• Thermowell specs: style, material, insertion (U), process connection, calculations per ASME PTC 19.3 TW-2016.

• Useful for simple local checks and laboratory use; filled with dyed alcohol or other safe fluids (mercury is restricted in many regions).
• Fragile; no remote mounting; slower response; limited pressure containment (use with a protective well).

• Visual inspection (window, dial, pointer zero at ambient), check for leaks/corrosion.
• Verify immersion, mounting angle, and that wells are not eroded; re-tighten unions.
• Periodic calibration based on criticality; replace damaged capillaries or bent stems.

• Use high-temperature alloys for wells (e.g., Alloy 600/625) and ensure case components are rated.
• Consider radiation shields, heat dissipating extensions, or remote bulbs to keep the dial in safe ambient.
• Verify creep and oxidation allowances; derate per vendor charts.

• Choose instruments rated for low ambient; gas-actuated systems often perform better at cryogenic ranges.
• Use low-temperature alloys and impact-tested materials for wells; prevent icing on dial and capillary.
• Account for heat leak through the well which can bias readings; use vacuum-jacketed wells if applicable.

1. Verify model, range, bulb/stem length, and thermowell specs vs datasheet and line class.
2. Install the well with correct gasket/torque (or weld/flange) and perform pressure test as required.
3. Ensure immersion depth, orientation, and clearance from inner wall; add lagging extension for insulation.
4. For remote units: route capillaries safely; avoid hot spots and tight bends; secure with clips/guards.
5. Stabilize process, check readings vs reference, record baseline, and set maintenance/calibration intervals.