API MPMS 7.4-2018 pdf download.Manual of Petroleum Measurement Standards Chapter 7—Temperature Determination Section 4—Dynamic Temperature Measurement.
6.3 Thermowell Thermowells are classified based on their use as test wells and sensor thermowells as explained in 6.3.1 and 6.3.2. 6.3.1 Thermowell Type 22.214.171.124 Test Thermowell Test wells are thermowells installed for occasional use, (temperature device verification, calibration and periodic fluid temperature measurement) and capped when not in use. Test wells shall be installed as close as practical to the sensor wells. A suggested maximum distance between the test well and sensor thermowell is three pipe diameters or 457 mm (18 in.) whichever is less. The test well should ideally match the sensor well thickness and construction materials and shall have the same immersion depth and a bore designed to accommodate the insertion of the verification temperature device. Capping prevents foreign material from accumulating in the wellbore. A clogged thermowell may cause measurement errors and may damage thermometers. It is recommended that thermowells be checked periodically for an accumulation of foreign material and cleaned if necessary. 126.96.36.199 Sensor Thermowell Sensor wells are thermowells installed for use with a permanently installed temperature device, and shall be matched to the temperature device. 6.3.2 Selection of Thermowell Thermowells shall be selected based on the application criteria described 6.3.3, 6.3.4, and 6.3.5. Calculations should be performed in accordance with ASME PTC 19.3 TW to confirm the appropriateness of each selected thermowell to resist flow-induced vibration.
6.3.3 Pressure Rating The thermowell selected shall comply with design codes for the operating pressures and temperatures of the system. 6.3.4 Installation The thermowell should be selected to conform to code and user installation practices. Thermowells are typically threaded, welded, or flange mounted. The immersion length of the thermowell should be sufficient to put the sensing portion of the device within the center one-third of the pipe diameter or provide immersion of 0.3 m (1 ft.) unless limited by fluid velocity considerations. The thermowell should be installed in as near to a vertical position as practical to allow it to be filled with an appropriate thermal-conducting material to cover the sensor. 6.3.5 Material The thermowell should be constructed of a material that is compatible with the liquid material that the thermowell is exposed to and should provide a degree of corrosion resistance for all surfaces. Usually Type 304 or 31 6 stainless steel is specified. 6.3.6 Thermowell Conductive Material In the case where the temperature sensor does not come into contact with the thermowell wall, the space between the sensor and the thermowell wall shall be filled with an appropriate amount of non-freezing thermal-conducting material to improve heat conduction between the wall of the thermowell and the sensor, and to improve the temperature sensor response time. 6.3.7 Electrical Temperature Sensor and Transmitter 188.8.131.52 Temperature Sensors Electronic temperature devices for dynamic measurement are usually housed in metal probes that mount into thermowells. The probes are generally tip sensitive. Therefore, the probes must be securely seated in the bottom of the thermowell for optimum temperature transfer. Spring loaded or adjustable length probes are recommended. If the probe cannot be seated in the bottom of the thermowell, an appropriate thermal-conducting material shall be used between the temperature sensor and the thermowell wall.
184.108.40.206 Resistance Temperature Detector A resistance temperature detector (RTD) is a sensor with an electrical resistance that is a function of temperature. The RTD is usually a small coil of platinum (or copper wire) and when used with appropriate circuits will provide temperature signals to readouts and other equipment. The RTD may be a resistance wire wound on a supporting nonconductive core, a thin film type, or other type. The element should be properly encased in a protective enclosure (probe), typically constructed of stainless steel. The electronic circuits should be intrinsically safe as required. The length of the temperature sensitive portion of a single- point (spot) element should not exceed 1 00 mm (4 in.). Three-wire or four-wire RTDs are recommended to compensate for lead length resistance. Refer to ASTM E11 37 for material and fabrication specifications and ASTM E644 for manufacturer calibration and testing of RTDs.