Introduction to boiler safety valve failure analysis

Safety valve is a very important protection valve widely used in various pressure vessels and piping systems. When the pressure in the pressure system exceeds the specified value, it can automatically open and discharge excess medium to the atmosphere. Go to ensure the safe operation of the pressure vessel and piping system to prevent accidents, and automatically shut down when the pressure in the system drops back to the working pressure or slightly lower than the working pressure. The reliability of the safety valve work is directly related to the safety of the equipment and the human body, so it must be taken seriously.

1. Analysis of common causes of safety valves and their solutions

1.1, valve leakage

Under the normal working pressure of the equipment, leakage exceeds the allowable degree at the sealing surface of the valve disc and the valve seat, and leakage of the safety valve not only causes media loss. In addition, the continuous leakage of the medium will also damage the hard sealing material. However, the sealing surface of the commonly used safety valve is made of metal material to metal material. Although it is intended to be smooth and smooth, it should be done under the condition of medium pressure. It is also very difficult to never miss. Therefore, for a safety valve whose working medium is steam, if the leak is not visible to the naked eye at the specified pressure value, the sealing performance is considered to be acceptable. It is known that there are three main reasons for the leakage of valves:

In one case, the dirt impurities fall on the sealing surface, and the sealing surface is padded, causing a gap between the valve core and the valve seat, so that the valve leaks. The way to eliminate this kind of fault is to remove the dirt and impurities falling on the sealing surface. Generally, when the boiler is ready to be shut down, the safety valve running test is first carried out. If it is found that the leak is stopped, the disassembly and repair are carried out. It is found that the safety door leaks during the running test after the furnace. It is estimated that this situation is caused by the fact that it can be cooled after 20 minutes of running, and then run the rudder once to flush the sealing surface.

Another situation is damage to the sealing surface. The main reasons for the damage of the sealing surface are as follows: First, the sealing surface material is poor. For example, in the main safety door of No. 3-9 furnace, due to years of maintenance, the sealing surface of the main safety valve spool and the valve seat has been generally studied very low, so that the hardness of the sealing surface is also greatly reduced, thereby causing a decrease in sealing performance, eliminating this The best way to do this is to turn the original sealing surface down and then re-surge the welding according to the drawings to improve the surface hardness of the sealing surface. Note that the processing quality must be guaranteed during the processing. For example, cracks such as cracks and trachoma on the sealing surface must be turned and reworked. Newly processed spool seats must meet the drawing requirements. At present, the effect of the valve sealing surface of YST103 universal steel electrode surfacing welding is better. Second, the quality of the inspection is poor, and the valve seat is not up to the quality standard. The method to eliminate the failure is to repair the sealing surface by grinding or turning after grinding according to the degree of damage. ?

Another cause of leakage of the safety valve is due to improper assembly or improper size of the part. During the assembly process, the valve seat is not completely aligned or the joint surface is transparent, or the sealing surface of the valve seat is too wide to seal. The elimination method is to check the size and uniformity of the matching clearance around the valve core, to ensure that the top hole of the valve core and the sealing surface are the same degree, and it is not allowed to lift the valve core to check the gap of each part; the width of the sealing surface is appropriately reduced according to the drawings to achieve effective sealing. . ?

1.2, valve body joint surface leakage

Refers to the leakage phenomenon at the joint surface between the upper and lower valve bodies. The main causes of such leakage are as follows: First, the bolt tightening force of the joint surface is insufficient or tight, resulting in poor sealing of the joint surface. The elimination method is to adjust the tightening force of the bolt. When tightening the bolt, it must be carried out in a diagonal manner. It is better to measure the gaps at the tight side, tighten the bolt until it is tight, and make the joint surface Consistent. Second, the toothed gasket of the valve body joint surface does not meet the standard. For example, the toothed seal has a slight groove in the radial direction, and the parallelism is poor, and the tooth shape is too sharp or over-slope to cause the seal to fail.

Thereby, the valve body joint surface leaks. The quality of the spare parts is checked during maintenance, and this phenomenon can be avoided by using a standard toothed gasket. Third, the flatness of the valve body joint surface is too poor or the hard impurities are padded to cause the seal to fail. The leakage of the valve body joint surface due to the poor flatness of the valve body joint surface is eliminated by disassembling the valve and re-grinding the joint surface until the quality standard is met. If the seal is ineffective due to the impurity being trapped, carefully clean the joint surface during the assembly of the valve to avoid impurities falling in.

1.3, the main safety valve does not move after the impulse safety valve is actuated

This phenomenon is often referred to as the rejection of the main security door. The main safety door refuses to damage the boiler in operation. It is a major equipment hazard, which seriously affects the safe operation of the equipment. Once the pressure of the pressure vessel and pipeline in operation exceeds the rated value, the main safety gate Do not operate, so that equipment overpressure operation can easily cause equipment damage and major accidents.

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Label: Introduction to boiler safety valve failure analysis

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