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This post was last edited by Jinma Water Damage Control on 2026-1-27 at 15:12. Temperature and pressure instruments are the most common types of instruments used in the field, serving to indicate the temperature and pressure of the media stored or transported as well as of the equipment itself. \"Safety Requirements for Port Operations – Part 1: Oil, Gas, and Chemical Terminals\" Pressure instruments, low-temperature detectors, and other such instruments and equipment must be in proper working condition, and they should be regularly calibrated or checked. \"Code for Selection and Design of Automation Instruments in Petrochemical Industries\" SH/T 3005: Instruments must be qualified products that have obtained a **manufacturing license**, and they must meet requirements regarding fire prevention, explosion protection, environmental protection, and energy efficiency. Classification of temperature instruments: Temperature is a key parameter in the storage and transportation of petroleum; it directly affects the fluidity of the oil, storage safety, and measurement accuracy. Common types of contact temperature instruments include: 1. Bimetallic thermometer: It uses two metal strips with different expansion coefficients; the degree of bending of these strips when heated determines the movement of the pointer, which indicates the temperature. It has a simple structure and allows for on-site reading, and is commonly used for on-site monitoring of pipelines and storage tanks. 2. Thermocouples/Thermistors (temperature transmitters): Convert temperature signals into electrical signals (such as 4-20mA) to enable remote transmission and automatic control. Thermocouples are suitable for high-temperature measurements, while thermal resistors offer higher precision and are often used for precise temperature control. Principle of thermal resistance: The resistance value of a conductor or semiconductor changes as the temperature changes. Principle of thermocouples: the thermoelectric effect of metals. Selection of temperature instruments: Range – the temperature range that the instrument can measure; when selecting one, it is necessary to ensure that it covers the highest and lowest temperatures that may occur in the process. Accuracy: The percentage of allowable error; for example, grade 1.0 means the error does not exceed ±1% of the range. Installation requirements: 1. The installation location should be able to accurately reflect the temperature of the medium; avoid installing it in dead corners of the pipeline or in areas with severe vibration. 2. When installing the temperature sensing element in the pipeline, it is necessary to ensure full contact with the liquid ； 3. If the pipe diameter used for installation is too small, the temperature sensing element should be installed on an additional expansion tube ； 4. The working end of the temperature measuring element should be located where the pipeline flow velocity is maximum ； 5. There must be sufficient insertion depth ； 6. The cover of the wiring box for thermocouples and thermal resistors should face upward, and there must be no strong magnetic fields around the thermocouples ； 7. To reduce the lag in temperature measurement, a filler with good heat transfer properties can be filled between the protective sleeves. Classification of pressure instruments: Pressure instruments are used to monitor the pressure in storage tanks, pipelines, and loading/unloading arms; they serve as the first line of defense against overpressure leaks and to ensure the safety of equipment. Bourdon tube pressure gauge (mechanical): It uses the deformation of the bourdon tube under pressure to drive a gear mechanism that moves the pointer; it features a simple structure and is durable, making it widely used for on-site pressure indication. There are also diaphragm pressure gauges (used for corrosive, highly viscous, crystallizing, or solid-particle-containing media) and electric contact pressure gauges (for alarm and remote transmission), among others. Pressure transmitter: Converts pressure signals into standard electrical signals for remote monitoring and interlock control. Selection of pressure instruments: The range of the pressure gauge should be chosen such that the pressure to be measured falls between 1/3 and 2/3 of the gauge’s range, in order to ensure accuracy in pressure measurement. The common pressure gauge ranges for storage and transportation systems are 1.6 Mpa, 2.5 Mpa, and 4.0 Mpa. Accuracy: The accuracy of a pressure gauge is determined by its maximum permissible error. The value obtained by removing the plus or minus sign and the percent sign from the maximum reading error is referred to as the accuracy class of the pressure gauge. The accuracy classes are specified as 0.1, 0.2, 0.5, 1.5, 2.5, and 5.0 respectively. Gauges used in storage and transportation systems are generally of grade 1.5 or grade 2.5. Allowable error = Range × Accuracy class. For example, a pressure gauge with a range of 10 MPa and an accuracy class of 1.6 has a maximum allowable error of ±0.16 MPa. Installation: The pressure gauge should be installed vertically to avoid the effects of vibration and high temperatures. Perform zero calibration regularly to check whether the pointer returns to zero and to detect any sticking. Fault analysis and handling: Unstable pressure gauge readings. Possible causes include excessive pipe vibration, severe pressure fluctuations, or blockages/leaks in the pressure piping. Remedial actions: Check whether the fixing bolts are loose, verify the process condition, and clean the pressure guide tube. Abnormal temperature display (too high or too low): Possible causes include damaged temperature sensing elements, loose wiring, and signal interference. Remedial action: Check the wiring terminals and use a multimeter to measure resistance or voltage values in order to determine whether the sensor is functional or not. Large fluctuations in readings: This may be due to air in the medium, improper damping settings of the instrument, or incorrect installation location. The process flow should be checked, the damping time adjusted (if applicable), or the installation location re-evaluated. No signal return: Use a multimeter to measure the circuit current; if it remains at 4 mA, check the power supply and fuse ； If the current fluctuates, check the damping and grounding. Leak emergency response: If a leak is detected at the instrument interface, the pressure relief valve (or root valve) should be closed immediately, and explosion-proof tools should be used to tighten it ； If it cannot be controlled, immediately activate the emergency plan, evacuate personnel, and report the situation.