Do pressure transmitters and thermal resistors used for measurement in chemical plants need to be calibrated regularly?
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For the process control instruments in our company, such as those for measuring pressure, temperature, flow rate, etc., aside from the instruments that are subject to mandatory regular calibration and a small number of important pressure switches that are calibrated annually, the rest are only calibrated or replaced when abnormalities occur. However, recently an upper-level authority conducted an inspection and stated that, according to the Metrology Law, all process instruments must be regularly calibrated. This is clearly impractical in a chemical plant, as it’s not possible to disassemble and inspect all instruments on a regular basis. How are others dealing with this issue? Are there any other relevant standards that specify the calibration requirements for routine process monitoring instruments?
Inspection must definitely be carried out; it can be done during the major maintenance of the equipment.
Instruments and meters that fall within the scope of the mandatory inspection list, namely the “List of Measuring Instruments Subject to Mandatory Control,” still require regular mandatory inspections. If it is not within the catalog range, calibration can be organized internally to ensure accurate measurements.
Preliminary research: Scope of mandatory inspection for pressure instruments: Used for safety protection: 1. Measurement of the main steam drum and feedwater pressure in power station boilers； 2. Measurement of the pressure in the air reservoir and main pipes of fixed air compressors ； 3. Measurement of generator and turbine oil pressure as well as locomotive pressure ； 4. Measurement of pressure with an alarm device ； 5. Sealing – Measurement of the pressure in pressurized containers ； 6. Measurement of pressure in harmful, toxic, and highly corrosive media
Mandatory inspection instruments are certainly subject to mandatory inspection in accordance with regulations, but for other ordinary measuring instruments, even if they are calibrated regularly – and even if the calibration is done by oneself – there are simply too many of them; it’s impossible to complete the calibration during a major maintenance period, as there aren’t enough people to handle them all. Just think about how many measuring points there are in a large chemical plant: that means there are countless instruments, thousands or even tens of thousands of them, and it’s simply unmanageable.
According to the classification of measuring equipment into A/B/C grades, measuring equipment that requires mandatory inspection is subject to periodic verification; equipment of grade B can be inspected during major overhauls or repairs, while equipment of grade C only needs to be inspected initially, with further verifications carried out every 2 to 4 cycles.
According to the Metrology Law, process control instruments, including pressure transmitters and thermal resistors, must undergo regular calibration. However, in practice, it is not practical to perform regular disassembly and inspection of all instruments. Chemical plants usually adopt the following methods to address this issue: 1. Develop a reasonable calibration plan: For important instruments, regular calibrations can be carried out at specified intervals ； For some secondary instruments, a approach of conducting calibration only when an anomaly is detected can be adopted, that is, calibration or replacement is carried out only when an abnormal condition occurs. 2. Based on equipment operation records: Utilizing the equipment operation records from instruments and making judgments based on experience, the calibration interval can be appropriately extended for instruments that have been operating normally over a long period of time. 3. Use reliability analysis methods: By employing reliability analysis methods, the reliability of the instrument and its failure probability are evaluated in order to determine the optimal calibration interval. In addition to the calibration requirements specified by metrological regulations, the following relevant standards can also be referred to: 1. The requirements for the testing and calibration of process control instruments as outlined in the standard **\"Guidelines for the Installation and Use of Industrial Instruments\" (GB50026-2019)**. 2. The industry standard \"Specifications for the Management of Automation Instruments in Chemical Enterprises\" (HG/T 5137-2016) also contains detailed provisions regarding the calibration requirements for process control instruments. In summary, for the process control instruments in chemical plants, it is recommended to establish a reasonable calibration plan. By combining equipment operation records with reliability analysis methods, the calibration interval can be determined based on actual conditions, in order to ensure the reliability and accuracy of these instruments. .
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It mainly depends on whether safety protections have been designed; if your transmitter is involved in interlocks or alarms, it falls into Category A. If it is used only for process monitoring and not on equipment such as boilers, it can be classified as Category B
Are the standards \"Guidelines for the Installation and Use of Industrial Instruments\" (GB50026-2019) and \"Specifications for the Management of Automated Instruments in Chemical Enterprises\" (HG/T 5137-2016) available? Could you send them to me so I can take a look?