From national special equipment safety information in 2018 in China, we can conclude as follows. In 2008, a total of 307 special equipment accidents occurred, with 317 deaths and 461 injuries, resulting in direct economic losses of 97,894,800 yuan. Among them, 17 accidents were directly caused by safety accessories failure or safety device damage. It accounts for 5.5% of the total number of special equipment accidents in 2008. The main problems are safety device failures or damage to boilers, pressure vessels, pressure pipelines, elevators, and lifting machinery.
On June 25, 2009, from the Guizhou Provincial Bureau of Quality and Technical Supervision of special equipment safety news release, we can know that in the first half of 2009, a total of 3 special equipment accidents occurred in the province, and 4 people were slightly injured. The direct economic loss is 31,000 yuan. Among them, there were 2 boiler explosion accidents and 1 sightseeing car accident. The two boiler accidents were caused by the failure of
safety valves, boiler over-pressure operation, and high-pressure boiler explosion.
From the above accident causes and problems, the situation that some special equipment units are heavy production and light safety still exists, especially in small and medium-sized enterprises and difficult enterprises. It is more difficult that they implement the safety responsibility. The enterprise reported the equipment inspected by itself with fatigue recognition and insufficient daily maintenance, which led to the hidden danger of accidents and resulted in accidents. We carried out the special equipment safety supervision regulations and established a special equipment safety production management system. Regular maintenance and inspection should be done for special equipment in use. Eliminate hidden dangers timely, and truly implement the main responsibility of the enterprise to ensure the safe operation of the special equipment in use.
Guizhou Pan Inspection Centre can undertake the pressure class special equipment of boilers, pressure vessels, pressure pipeline inspection and safety accessories, calibration and maintenance tasks of safety
valves, and pressure gauges. At the same time, the units have an obligation to the special equipment. The goal is to work hard to "quality and safety" and special equipment "three actions" work. Effectively ensure the safety of equipment operation. Therefore, this paper mainly on the related knowledge of safety valves, common malfunctions, and elimination methods of safety valves. The maintenance and inspection methods are introduced, in order to communicate and learn with special equipment using units and inspection units.
1. The safety valve is an important safety accessory for pressure special equipment
The safety valve is an automatic valve, which does not use any external force and the force of the medium itself to discharge a rated number of fluids in order to prevent pressure over the rated safety value. When the pressure returns to normal, the valve closes again and stops the flow of the medium. The safety valve is an important safety accessory of special pressure equipment such as boilers, pressure vessels, and pressure pipelines. It is a safety device set to prevent explosions caused by excessive pressure in abnormal conditions. It plays an important role in the safety and economy of equipment. Therefore, the State Council of the People's Republic of China for the special equipment safety supervision regulations and related rules and regulations of safety technology require that we need to ensure the effectiveness and timeliness of regular calibration of safety valves.
On May 8, 2009, the State Administration of Quality Supervision promulgated the safety technical Supervision procedures No. 1 revision list of safety valves. The design, manufacturing, inspection, installation, use, calibration, and maintenance of the process of advancement of safety valves are ruled. The consistency of the existing procedures and management methods has provisions in practice. In line with and complying with the "Special equipment safety supervision regulations" requirements, we can ensure the safety of the safety valve in boilers, pressure vessels and pressure pipelines, and other pressure equipment for safe use.
2. Contents to be indicated the on the nameplate of safety valves
The nameplate of the safety valve or the outer surface of the safety valve shall be clearly marked with at least the following contents, such as the number and mark of the safety valve, the manufacturing license, the name of the manufacturer, the structural type of the safety valve, the date of manufacture and its product number, the nominal pressure (pressure level), the nominal diameter, the diameter or area of the flow channel, the set pressure, the material of valve body, the rated discharge coefficient and the rated discharge guaranteed for a certain fluid. The nameplate should be made of corrosion-resistant material and must be securely fixed to the outer surface of the valve body or bonnets.
3. The common malfunctions and elimination methods of safety valves
Safety valve failures are mainly caused by poor design, manufacture, or selection. If these malfunctions are not eliminated in time, they will affect the efficacy and life of the safety valve. Even it can not play a role in safety protection. Personnel engaged in the operation and maintenance, disassembly, and inspection of the safety valve in use shall obtain the Special Equipment Operator Certificate. Common malfunctions and troubleshooting methods are as follows.
(1) Leakage. Under the normal working pressure of the equipment, the leakage between the valve disc and the surface of the seat sealing of valves exceeds the allowable degree. The reason is that there is dirt between the valve disc and the valve seat sealing, you can use the lifting wrench to open the valve several times to wash away the dirt. The damage to the sealing surface should be repaired by grinding or grinding after turning according to the degree of damage. If there is valve stem bending, tilt, or lever and fulcrum deflection, it should be reassembled or replaced. Spring elasticity is reduced or the elasticity lose, it should be taken to replace the spring, readjust the opening pressure, and other measures.
(2) Do not open to the specified pressure. The reasons for this are as follows.
The constant pressure is inaccurate. The compression of the spring or the position of the hammer should be readjusted. Disc sticks to the seat. The safety valve should be manually discharged regularly. The lever type safety valve lever is stuck or a heavy hammer is moved. The position of the weight should be readjusted and the lever movement should be automatic.
(3) Less than the prescribed pressure to open. The main reasons are the inconstant pressure, spring aging, and spring decline. It should be adapted to tighten and adjust the stem or replace the spring.
(4) The pressure continues to rise after discharge. This is mainly because the discharge capacity of the selected safety valve is less than the safe discharge capacity of the equipment, so the appropriate safety valve should be re-selected. If the center line of the valve stem is not correct or the spring is rusty the valve clack cannot be opened to its proper height. The valve stem shall be reassembled or the spring shall be replaced. If the section of the exhaust pipe is not enough, the exhaust pipe conforming to the safe discharge area shall be adopted.
(5) Frequency hop or vibration of the valve disc. It is mainly because the spring stiffness is too large. We should be used to appropriate stiffness spring. The adjustment ring is not properly adjusted, and the pressure of the seat is too high. The position of the adjustment ring should be re-adjusted. The resistance of the discharge pipe is too large, resulting in too much discharge back pressure.
(6) The disc does not return to the seat after discharge. This is because the spring is bent, and the installation position of the stem and disc is not correct or stuck. It should be reassembled.
