Common problems of heating furnace safety valve gate valve Analysis Basic knowledge of safety valve

Common problems of heating furnace safety valve gate valve Analysis Basic knowledge of safety valve

1. Preface
Safety valve is a vital maintenance gate valve, used for a variety of high pressure vessels and conveying pipes, when the working pressure in the stress system exceeds the standard value, it can automatically open, the excess material discharged into the air, to ensure the safe operation of high pressure vessels and conveying pipes, to avoid the occurrence of events, But when the pressure in the system software drops back to pressure or slightly below pressure, it can automatically exit. Safety valve related work is directly related to the safety of equipment and personal safety, so we must give high attention to.
2. Root causes and solutions of common problems of safety valve
2.1, gate leakage 
Under the normal operating pressure of the system, the leakage of piston valve and high pressure gate valve at the sealing surface exceeds the allowable level, and the leakage of the safety valve will not only cause material damage. In addition, the medium will continue to leak hard rubber seals will be damaged, however, the sealing surface of the common safety valve is all metal composite materials to metal materials, although to do smooth and orderly, but it is very difficult to ensure water leakage under the premise of material pressure relief. Therefore, for the medium is the vapor safety valve, under the specified system pressure, if the naked eye can not see at the entrance and exit end, also can not hear the leakage, think that the tightness is in line with the requirements. Generally, there are three main reasons for gate valve leakage:
One case is that the dirty residue falls into the sealing surface, and the sealing surface is covered, resulting in a gap between the spool and the high pressure gate valve, and then the gate valve leaks. The way to remove this kind of common fault is to explode into the dirt and residue in the sealing surface, generally in the heating furnace in advance to prepare the boiler blow pipe size repair, the first to do the safety door lead experiment, once found to leak boiler blow pipe also carried out collapse maintenance, if it is after the furnace to run the lead test found that the safety door leak, may be caused by such a thing, The lead can run after 20 minutes of refrigeration and then run a rudder, the sealing surface to carry out washing.
Another situation is the sealing surface damage. The main reasons leading to the sealing surface damage are as follows: First, the sealing surface material is poor. For example, in No. 3 ~ 9 furnace main safety door because of years of maintenance, the main safety door spore and high pressure gate valve sealing surface has been widely studied very low, so that the sealing surface hardness is also reduced, resulting in reduced sealing, the more appropriate way to remove this situation is to milling down the original sealing surface, and then according to the engineering drawings again spray welding production and processing, Enhance the hardness of the sealing surface. Pay attention to the production quality must be ensured in the production process, such as the sealing surface cracks, sand holes and other shortcomings must be milling down after production and processing. The new processing spool high pressure gate valve must meet the engineering drawing standards. At present, the application of YST103 universal steel welding rod spray welding processing to make the valve core sealing surface is very good. Second, the maintenance quality is not good, the spool high pressure gate valve grinding can not meet the product quality standards, the way to remove this kind of common faults is to use the grinding or milling method to repair the sealing surface according to the degree of damage.
Another major cause of safety valve leakage is improper installation or the size of the relevant parts is too large. In the installation link, the spool high pressure gate valve has not been right or there is light leakage on the joint surface, or the sealing surface of the spool high pressure gate valve is too wide to seal. Check the size and uniformity of the clearance around the spool assembly, ensure that the front end hole of the spool and the sealing surface are the same, and detect the voids everywhere can not extend out of the spool; According to engineering drawings, the width of sealing surface should be reduced to achieve reasonable sealing.
2.2 bonding surface leaking oil circuit board, 
Refers to the water leakage problem at the indirect surface of the oil circuit plate, leading to this kind of leakage is the following important reasons: first, the joint surface of the anchor bolt tightening force is insufficient or tight, resulting in the joint surface sealing is not very good. What is the cleaning method to adjust the bolt tightening force? When tightening the anchor bolt, it must be carried out in the form of tightening according to the top Angle. It is better to accurately measure the space in each place and tighten the anchor bolt until it does not move, so as to make the joint surface the same space in each place. Second, the oil circuit plate joint surface tooth type sealing gasket does not meet the requirements. For example, tooth type sealing gasket axial slight groove, flatness, tooth type too sharp or slope and other shortcomings will lead to ineffective sealing. So that the oil circuit plate joint surface leakage. In the maintenance of parts quality control, the selection of standardized tooth sealing gaskets can avoid this kind of situation. Three is the oil circuit plate joint surface flatness is very poor or hard residue pad resulting in ineffective sealing. For the oil circuit plate joint surface caused by poor smoothness of the oil circuit plate joint surface water leakage, the way to remove is to collapse the gate valve and grinding the joint surface again until it meets the product quality standards. Because of the residue pad caused by the sealing does not work, in the gate valve assembly carefully remove the joint surface to prevent the residue falling into.
2.3, impulse safety valve posture Shu main safety valve posture
This condition is also known as primary safety gate rejection. The main safety door is closed to the use of heating furnace damage is very great, is a major equipment hidden danger, serious harm to the safe operation of machinery and equipment, once the use of high pressure vessels and pipelines in the material working pressure beyond the rated current, the main safety door is not posture, so that the overpressure operation is easy to cause damage to machinery and equipment and major safety accidents.
Before studying the main reasons for the main safety door refusing to move, first analyze the basic principle of the main safety door operation. As shown in Figure 1 below, when the pressure in the pressure vessel rises to the whole pressure of the impulse relief valve, the impulse relief valve position, the material runs from the container to the main safety valve piston room according to the pipe, in the piston room there will be a slight expansion of blood pressure reduction, if the gas pressure in the piston room is P1, the piston throttle area is about Shs, then the f1 acting on the piston is:
F1 = P1 by Shs…………………………………… (1)
If the pressure of the medium gas in the pressure vessel is P2, and the area of the valve core is about Sfx, then the interaction force f2 of the material pushing upward on the valve core is:
F2 = P2 x Shx … (2)
General relief valve piston aperture diameter of the valve core is large, so the type (1) and (2) the type of Shs > Sfx  P1 material P2
If the torsion spring is set as f3 and the sliding friction force between the fitness component and the fixed component (usually the sliding friction force between the piston and the piston chamber) is set as fm according to the tensile force of the valve seat against the spool, the prerequisite for the operation of the main safety door is: Only when the interaction force f1 acts on the piston is slightly larger, the interaction force f2 used on the spool to push it upward, the tension resistance of the torsion spring to the spool upward according to the valve seat f3 and the sliding friction force between the fitness component and the fixed component (usually the sliding friction force between the piston and the piston chamber) fm sum, namely: The main safety gate can be operated only when f1 > f2 f3 fm.
In practice, the main safety door rejection may be related to the following three aspects:
One is the gate valve fitness sports components are stuck. This may be because of unreasonable installation, dirt and residue infiltration or parts erosion; Piston chamber surface smoothness is poor, surface damage, grooves and other shortcomings caused by hard grain. In this way, the sliding friction force between the fitness component and the fixed and stationary component will be expanded. Under the premise that the other requirements remain unchanged, f1 < f2 f3 fm is therefore rejected by the main safety door.
For example, in No. 3 furnace maintenance before the overtemperature main safety door running weight test, the main safety door refused to move. During the inspection of collapse during maintenance, it was noted that there were a lot of rust and residue in the piston room, and the piston could not exercise in the piston room, which caused the main safety door to refuse to move. In the process of maintenance, the piston, the expansion ring and the piston chamber are treated with rust prevention, and the shortcomings of the piston chamber are ground. Before installation, the inner wall of the piston room is evenly coated with lead powder, and the valve body is assembled in strict order. In the heating furnace pressure test, the single pulse tube is washed, and then the main safety door is connected with the impulse safety valve, and the safety valve running weight test is carried out again when the furnace is repaired. Everything is normal.
Second, the main safety door piston chamber leakage is large. When the air leakage in the gate valve piston chamber is too large, the interaction force of f1 in Formula (1) acting on the piston is small. On the premise that other requirements remain unchanged, f1 < f2 f3 fm is therefore rejected by the main safety door. The important reason leading to large leakage in the piston chamber is related to the sealing of the gate valve itself and the piston ring does not conform to the specifications or the piston ring is too damaged to meet the sealing requirements.
For example, 3 ~ 9 furnace main safety valve for piston ring quality basic requirements piston ring corner should be rounded, free state gap shall not exceed 14, after assembly mouth gap △=1 ~ 1.25, piston and piston chamber gap B=0.12 ~ 0.18, piston ring and piston chamber gap S=0.08 ~ 0.12, piston ring and piston chamber contact good, Light transmittance should not exceed 1/6 diameter. For the basic requirements in the piston room, the deep depth of the pipe groove in the piston room shall not exceed 0.08 ~ 0.1mm, its ovality shall not exceed 0.1mm, the cone degree shall not exceed 0.1mm, and it shall be smooth and unabrassible. However, during the inspection of the collapse maintenance, it is noted that the piston ring, piston and piston chamber of each main safety door of the furnace do not conform to the maintenance regulations. At the present stage, the clearance between piston ring and piston chamber is generally S≥0.20, and the shortage of piston chamber surface is more serious, which greatly affects the steam tightness of piston part, resulting in slightly larger steam leakage of piston chamber.
Such shortcomings can be eliminated by: To solve the internal position of the piston room, replace the piston and piston ring that meet the requirements, adjust the opening degree of the relief valve in the impulse safety device system of the relief valve, increase the amount of steam into the main safety door piston part, under the condition of permitting, it can also increase the amount of steam into the main safety door piston room by lifting the stroke of the impulse safety valve to promote the position of the main safety valve.
Third, the pairing of the main safety valve and the impulse safety valve is unreasonable, and the steam flow of the impulse safety valve is too small. The nominal diameter of the impulse safety valve is too small, leading to the reduction of steam injected into the piston part of the main safety valve, and the insufficient force f1 to promote the downward movement of the piston, that is, f1 < f2 f3 fm leads to the main safety valve spool is not moved. This is often the case when the main safety valve impulse safety valve has a replacement, because it is not well considered and caused by.
For example, when No. 5 furnace is being repaired, two heavy hammer impulse safety valves are replaced with two A49H-P54100VDg20 pulse safety valves produced by Harbin Valve Factory. This safety valve is generally applied with A42H-P54100VDg125 spring type main safety pair. Put it with Su production Dg150×90×250 type old main safety valve used, this kind of main safety valve and A29H-P54100VDg125 type spring type main safety valve is larger than the nominal diameter and the tightness is weak, in No. 5 furnace saturated state safety valve weight end, carry out the test lead lead to the main safety valve rejection. Finally, we will collapse the impulse safety valve, the guide sleeve and the spool cooperate with each other part of the gap expansion, in order to enhance its total current carrying area, run the lead again a successful experiment. So the impulse safety valve and the main safety valve pairing is not reasonable, nominal diameter ratio will cause the main safety valve rejection.
2.4, impulse safety valve back seat Shu main safety valve delay time back seat time is too long
The main reasons for these common faults are as follows:
On the one hand, the leakage size of the piston part of the main safety valve, although the impulse safety valve back seat, but there is also the steam pressure in the pipeline and piston chamber is still very high, promote the piston down force is still very large, so lead to the main safety valve back seat slowly, this kind of common failure more than A42Y-P5413.7VDg100 safety valve, Because of this form of safety valve piston chamber seal good. The way to remove this kind of failure is mainly by amplifying the opening degree of the relief valve and increasing the throttle valve diameter to solve, the opening degree of the relief valve and the throttle valve diameter increase to leave the steam in the monopulser tube quickly discharged, so as to reduce the working pressure in the piston, so that it is used for the piston to move down the driving force rapidly reduced, The valve spool in the collection of steam material in the exhaust box to drive up the driving force and the main safety valve itself torsion spring to drive up under the influence of the tension quickly back to the seat.
On the other hand, because the friction between the moving components of the main safety valve and the fixed components is too large, the main safety valve will also lead to slow seat, to deal with this kind of problem is the main safety valve fitness sports components and fixed parts of the assembly gap control panel within the scope of the specification.