Common problems and precautions of power station boiler safety valve

First, the role of power station boiler safety valve and features Safety valve is an important annex to the boiler, when the boiler pressure vessels (such as drums, superheater, reheater, etc.) and the pipeline pressure, exceeding the normal, and to take off pressure The valve opens automatically. Exhaust too much steam, so that the pressure back to normal, to protect the equipment, personal safety, when the pressure returned to normal pressure, the valve automatically shut down, the safety valve requirements are the following: 1, the safety valve has sufficient sensitivity , When the pressure reaches the take-off pressure should be open without obstruction 2, the safety valve in the prescribed circumstances, the valve should be fully open, and discharge the rated amount of exhaust 3, when the pressure dropped to the back seat pressure, the valve should Closed in time and maintained in close state Second, Huade Power Plant boiler installed safety valve Introduction Huade Power Plant Phase I and II boilers were put into operation in 1991-1994, respectively, with four Harbin boiler plant HG1025-18.2 / 540/540-PM sub-critical natural circulation drum boiler, each boiler superheater outlet manifold installed two spring-loaded safety valve, a solenoid valve, the top of the drum at both ends of the installation of a total of 3 Only spring-loaded safety valve, reheater inlet and outlet manifold installed three spring-type safety valve for the introduction of Japan's Harbin Boiler Factory Okano technology production; III boiler for the German company Babcock can produce DB2029-18. 67-541 / 541-PM subcritical natural circulation drum boilers were put into production in July and October 2002 respectively. Two spring-loaded safety valves and one electromagnetic discharge were installed on the superheater outlet manifold of each boiler. Valve, the drum at the top of each installation of three spring-loaded safety valve, reheater outlet manifold installed four spring-loaded safety valve, the inlet manifold installed five spring-loaded safety valve for the United States Crosby company design and production. Third, the Howard Power plant drums and the main reheater safety valve in the operation of the common problems and treatment methods 1: running leaks, safety valve take-off, the impurities stuck at the end of the valve junction leak, until the pressure dropped to take off pressure 75% or so manually re-test, under normal circumstances no longer after the release of seat leakage. 2: After the safety valve takes off, do not go back to the seat, the spring may be jammed, and the pressure of the main pipe should be rapidly reduced. Open the manual test cap and gently tap the top of the valve stem with the hammer to return to the seat. Leakage, manual test after the leak is still due to the safety valve exhaust time is too long, so that the rigidity of the spring to reduce the load in the boiler stable until the safety valve exhaust chamber cooling, the leakage will be eliminated. 3: the safety valve in operation, if the phenomenon of frequent take-off, not only easy to damage the bonding surface, but also easy to system damage caused by shock, mainly due to the safety valve opening and closing pressure is too small, usually due to the nozzle ring fixing bolt Damage, causing the nozzle ring shift caused by frequent take-off is also easy to make the spool pressure on the nozzle ring move so that the valve core can not be well combined with the valve, resulting in serious leakage, the general operation of the nozzle ring is difficult to adjust, Large amount of leakage, was forced to shut down for processing. 4: Safety valve in operation beyond the take-off pressure, can not afford to seat, under normal circumstances is due to the safety valve spring and valve stem astringent, the pressure dropped to take off about 75% of the pressure to manually re-test, you can eliminate This phenomenon; another phenomenon, the safety valve actually jump value is higher than the design value, should be based on the safety valve spring stiffness values ​​adjusted to meet the design take-off pressure, pay attention to the system pressure must be reduced to 75% of the specified pressure Can carry on 5: The safety valve in operation jumps ahead of the designed jump value. The actual jump value of the safety valve is indeed lower than the designed value. It should be adjusted according to the stiffness value of the safety valve spring so that it conforms to the design take-off pressure. Pay attention that the system pressure must be reduced to 75% of the specified pressure can be carried out. 6; According to the provisions of the pressure vessel, the actual take-off test at least once a year, the current practice is the size of the pre-repair manual test to check whether the safety valve spring jam, with the existence of defects in the interface, After the completion of the value of the jump, choose a jump value of the lowest take-off to verify the calibration results, the pre-test pull the safety valve repair judgment is a very important part of the pre-trial pull test, decided to disintegrate After the safety valve, should focus on checking what components, what kind of overhaul. Fourth, the safety valve repair should pay attention to the problem 1: Pre-repair test found that the safety valve can not be normal take-off, you should first check the valve stem and bonnet the top of the distance between the meet the requirements, after the adjustment is completed, and then try again, if There is no normal take-off exhaust, disassemble the safety valve, you should first check the spool and the sleeve if there is jam, I plant in May 2004 # 1 boiler overhaul once found reheater inlet # 1 safety The valve can not afford to seat, disassembled and found the spool stuck together, after heating only remove the spool, only to replace the sleeve; Second, for the safety valve with a spring cover, the spring cover should be disassembled, check the spring and the stem With the gap, the valve stem is bent 2: Found before the relief valve leaks, after treatment can not eliminate the phenomenon of leakage, the first check after the collapse of the valve core is not in full contact with the valve, but the pressure in the nozzle ring, if there is The nozzle ring and valve spool contact traces should focus on check the nozzle ring fixing bolts (some safety valve fixing bolts and adjusting rod for the same part) is damaged, and secondly check the fixed cap is tightened, Rotating nozzle ring should be, but not more than two teeth manufacturer predetermined number. 3: disassemble the check valve with the safety valve, if there is stuck on the bonding surface of the formation of scratches, indicating leakage is due to the bonding surface stuck impurities caused by the abrasive block coated abrasive grinding, note that when the erosion of deep groove , You can grind it with coarse sandpaper first, but in the last step, you must grind and polish it with abrasive sand (fine sand particles contained in the abrasive is 600 or 900) to ensure the flatness of the bonding surface. 4: disassembled safety valve check with the surface, if there is no stuck on the bonding surface of the formation of flawed, indicating leakage is caused by the spool deflection, uneven surface contact, valve stem should be checked at the junction of the center of the pair Positive, the positioning pin on the stem is damaged, bending, resulting in valve stem and valve center misalignment, uneven preload; 5: for the combination of scouring traces, bonding surface grinding, should pay attention to the formation of grinding flat Degree and force direction, the grinding block is a special grade made of annealed cast iron, both sides are very smooth, to grind a sealing surface, it must be kept flat, each time before using the grinding block must be machine (generally use planer) For processing and grinding; the grinding block placed on the sealing surface grinding, prohibit the continuous rotation of the grinding block, but should be back and forth way to grinding. 6: When assembling, pay attention to the positions of the nozzle ring and the guide ring conforming to the designed values. The fixing bolt (adjusting rod) must be placed in a groove of the nozzle ring and the guide ring. The external spare cap must be fastened, At the same time to clean the exhaust chamber impurities, exhaust chamber drain pipe to install a solid, smooth, valve body connecting bolts must be identified before the complex material and hardness identification, the nozzle ring and the flow guide ring, stem, screw thread Apply smear oil, prevent rust corrosion, resulting in parts jam can not be adjusted. 7: Since the boiler above the high pressure in the overhaul or replacement of the heated surface of the pipe, the general hydrostatic test, the safety valve involved in the hydrostatic test in the hydraulic test, the use of special hydrostatic test spool, the top of the stem placed anti- Seat block or top wire to prevent the safety valve during the experiment, the seat, after the test is completed, remove the test valve, restore the original safety valve spool. 8: As the safety valve overhaul, the spring tension inevitably changed, so the size of the fuselage repair body safety valve, the thermal pressure must be verified, due to the current widespread use of online pressure calibration instruments, a high degree of automation, school Valuation is very accurate comparison is simple. However, it should be noted that when checking the thermal state, the system pressure must be kept stable at about 65% -75% of the design pressure. When more than 3 times of take-off still fail to meet the design take-off pressure, the verification should be stopped and the safety valve should be cooled before proceeding Re-check. V. Through the implementation and improvement of a series of overhaul technologies mentioned above, our factory reheater safety valve has been seldom leaked in stage I and II boiler safety valves since 1995, and the safety valve takes off accurately. However, since 2002 III Since the boiler was put into operation, the phase III boiler safety valve components and I, II have significant differences, although the take-off accurate, but the operation of drum valve safety valve leakage rate higher than the effect of phase I and II boiler safety valve slightly Poor, is now gradually exploring its solutions for the safe operation of the boiler to create a good foundation, the above points are inadequate, please colleagues and experts criticism correction, if you have good suggestions, please contact the discussion to promote our safety Valve maintenance technology improvements.

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