Online calibration and deferred calibration of safety valves

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I. Principle of online calibration technology for safety valves The basic principle of online calibration of safety valves is as follows: When the safety valve is installed on the equipment it is meant to protect, the technician connects a lifting device to the valve stem. An external lifting force is applied either through a pump or manually; this external force, together with the initial pressure of the medium, counteracts the spring preload acting on the valve disc. When these two forces cancel each other out, that is, when the sealing force between the valve disc and the seat is zero, the valve disc separates from the seat. The value of this external lifting force at that moment is measured, and by using the effective area of the sealing surface of the safety valve, the set pressure value at the moment the valve opens can be determined. II. Advantages and disadvantages of online calibration technology for safety valves (1) Advantages. 1) Improve corporate production efficiency, reduce costs, and lower the workload for employees. Online calibration eliminates the need for disassembly, installation, or production shutdowns; it also avoids procedures such as system isolation. This saves time and effort associated with shutdowns, disassembly, lifting, and transportation, thereby improving the production efficiency of enterprises as well as the efficiency of safety valve calibration. 2) Address the impact of thermal errors on the opening pressure of safety valves. The behavior of the safety valve spring differs between hot and cold conditions. Online verification is carried out under actual operating conditions, without the need for temperature correction, and it addresses the impact of temperature on the opening pressure more effectively than testing at low temperatures. 3) Overcome the influence of system backpressure on the opening pressure of the safety valve. Online verification is carried out under actual operating conditions, effectively addressing the impact of backpressure factors to ensure the proper operation of the device. 4) Address the error factors between the valve stem spring seals. Online calibration of safety valves takes into account all the errors between the valve stem, spring, and seals. This technology pays special attention to its sealing conditions, continuously applying force to the valve stem that is being tested, recording relevant data under the actual conditions of stress on the valve stem, and conducting scientific analysis thereof. (2) Disadvantages. 1) Online calibration of safety valves involves many uncontrollable factors on-site, resulting in a higher risk level compared to calibration at low temperatures ； 2) Sealing performance tests cannot be conducted at present. III. Regulatory basis for online calibration technology of safety valves: \"TSG ZF001-2006 Regulations on Safety Technical Supervision of Safety Valves\" – B6 Periodic inspections; B6.1 Online inspection and testing. B6.1.1 Meaning of online inspection and testing and requirements for personnel: Online inspection and testing refers to the inspection and testing of safety valves while they are in operation (i.e., when the safety valves are installed on equipment and under pressure or not under pressure). Personnel engaged in online inspection should have received professional training in equipment operation, the use of online inspection devices, and on-site problem resolution, and should hold certificates for working with special equipment. B6.1.2 Inspection contents Online inspection includes the following: (1) Whether the safety valve is installed correctly ； (2) Are the documents for the safety valve complete (nameplate, quality certification documents, installation number, verification records, and reports)? ； (3) Is the seal of the safety external adjustment mechanism intact? ； (4) Are there any factors that affect safe and normal operation? ； (5) When it is necessary to install cut-off valves, check whether the lead seals of these valves are intact and in their normal open position, both before the inlet and after the outlet of the safety valve ； (6) Whether the safety valve is leaking ； (7) Check for corrosion on the exterior of the safety valve ； (8) The vent holes provided for the bellows should be open and clean ； (9) The lifting device (wrench) functions properly and is in the correct position ； (10) The external accessories related to the safety valve are intact and in good condition. B6.1.3 Detection Methods The online detection methods are as follows: (1) Tests are conducted using the protected system and its pressure ； (2) Use other pressure sources for testing ； (3) Use an auxiliary opening device for the test. B6.1.4 Basic requirements for inspection work Online inspection work must also meet the following basic requirements: (1) Before conducting online inspection, the safety valve to be inspected shall be checked in accordance with B6.12 ； (2) During online testing, the testing unit shall establish practical testing procedures and make all necessary material and technical preparations ； (3) During online monitoring, the competent technical personnel of the using unit must be present; whenever signs of deviations from normal operating conditions are detected, operations must be stopped immediately and appropriate measures taken to ensure safety ； (4) During online monitoring, it is necessary to take care to prevent high-temperature noise and medium leakage from causing harm to personnel ； (5) The online monitoring device can ensure the basic performance requirements of the safety valve ； (6) Keep proper records of online inspections and tests, and archive them. IV. Regulatory basis for the technology of delaying the calibration of safety valves. Regulation 1: \"TSG ZF001-2006 Regulations on the Safety Technical Inspection of Safety Valves\" B6.3.1 Calibration cycle: The calibration cycle for safety valves shall meet the following requirements: (1) Safety valves should be calibrated regularly, at least once a year; if there are corresponding provisions in the safety technical specifications, those provisions shall apply ； (2) Safety valves that have been disassembled, repaired, or had their components replaced shall be recalibrated. B6.3.2 Extension of calibration period The calibration period for safety valves can be appropriately extended when the following basic conditions are met; the extent of the extension is determined in accordance with the relevant safety technical specifications: (1) There are clear historical records indicating the reliable operation of the safety valves on the equipment being protected ； (2) The operating process conditions of the protected equipment are stable ； (3) The materials of the safety internals have not been corroded ； (4) Both online inspection and online testing of the safety valve meet the usage requirements ； (5) There are comprehensive emergency response plans. For equipment required for production to operate continuously for a long period of time of over 1 year, the calibration interval for safety valves can be appropriately extended, subject to conditions such as the actual usage patterns of similar equipment, the reliability of the equipment’s manufacturing quality, as well as the safe and reliable measures adopted in production operations; and provided that these requirements are met in accordance with these regulations. Regulation 2: \"TSG 21-2016 Safety Technical Inspection Regulations for Fixed Pressure Vessels\" 7.2.3.1.3 Period for safety valve calibration 7.2.3.1.3.1 Basic requirements Safety valves should generally be calibrated at least once a year; under the special conditions specified in 7.2.3.1.3.2 and 7.2.3.1.3.3, the calibration period may be extended appropriately with the approval of the person in charge of safety management at the using unit. 7.2.3.1.3.2 The inspection period can be extended to 3 years. Spring-loaded safety valves can have their inspection period extended up to 3 years if they meet the following conditions: (1) The manufacturer of the safety valve can provide proof that the springs used have been subjected to high-pressure treatment or heat-treated under high pressure in accordance with GB/T 12243 \"Spring-loaded Safety Valves\"; furthermore, 10% of the springs of the same specification from the same heat treatment furnace (but not less than 2 springs) should be tested for their deformation or stiffness under specified loads, with the deviation in the test results being no more than 15% ； (2) The material of the safety valve’s internal components is resistant to corrosion by the medium ； (3) The safety valve has not opened during normal operation ； (4) Pressure vessels and their safety valve bodies show no obvious rust during use ； (5) Pressure vessels containing non-sticky media with a moderate or lower level of toxic hazard ； (6) The user unit has established and implemented sound systems for the use, management, and maintenance of equipment, and is equipped with reliable pressure control and regulation devices or overpressure alarm devices ； (7) The user unit has established a safety valve calibration station that meets the requirements and possesses the capability to calibrate safety valves. 7.2.3.1.3.3 The inspection period can be extended to 5 years. For spring-loaded safety valves that meet the conditions specified in items (2), (3), (4), (6), and (7) of section 7.2.3.1.3.2 of these regulations, the inspection period may be extended up to 5 years provided that the following conditions are also satisfied: (1) The manufacturer of the safety valve can provide proof that the springs used have been subjected to high-pressure treatment or heat-treated under high pressure in accordance with GB/T 12243; furthermore, 20% of the springs of the same specification from the same heat treatment furnace (but not fewer than 4 springs) were tested for their deformation or stiffness under the specified load, with the deviation in the test results being no more than 10% ； (2) Pressure vessels containing gas media with a mild level of toxicity (non-toxic), at operating temperatures not exceeding 200°C. 7.2.3.1.4 On-site Verification and Adjustment: When a safety valve requires on-site verification (online verification) and pressure adjustment, the safety management personnel responsible for pressure vessels at the using unit, as well as the personnel tasked with the maintenance (verification) of the safety valves, must be present to oversee the process. A properly calibrated safety valve should be sealed with a lead seal. The accuracy of the pressure gauge used for verification and adjustment devices must be at least grade 1. Reliable safety measures should be in place during checksum verification and adjustment.