| The root cause of stainless steel gate valve stem fracture and deformation |
| 发布日期：2021-10-26 15:14:53 点击数：541 次 新闻来源： |
The root cause of stainless steel gate valve stem fracture and deformation
The gate plate of the stainless steel gate valve moves linearly with the valve stem. Usually there is a trapezoidal thread on the lifting rod. Through the nut on the top of the valve and the guide groove on the valve body, the rotary motion is changed into linear motion, that is, the operating torque is changed. Change to operating thrust. The sealing surface can only rely on the medium pressure to seal, that is, relying on the medium pressure to press the sealing surface of the gate to the valve seat on the other side to ensure the sealing of the sealing surface, which is self-sealing. Most gate valves use forced sealing, that is, when the valve is closed, the gate must be forced to the valve seat by external force to ensure the sealing performance of the sealing surface. Gate valves are more and more widely used in various industrial systems due to their advantages such as pressure resistance, temperature resistance (high and low temperature), corrosion resistance (multiple material configurations), two-way sealing function, wear resistance and long service life. The opening and closing of the system play an important role in the stability and control of the system. Stem fracture analysis of stainless steel gate valve: The valve stem fracture generally occurs at the roots of the upper and lower threads, where the cross-sectional area is the smallest, which is prone to stress concentration and exceeding the standard. Especially when the working conditions deviate greatly from the design parameters. An accident occurred when the valve stem was pulled off at the trapezoidal thread undercut groove after the gate valve was opened. The investigation found that the valve bonnet pre-tightening nut was loose, the bonnet moved up, and the stem nut was stuck. Obviously, this was an accident caused by over-adjustment of the Denso stroke and excessive protection torque. Another type of valve stem fracture accident occurred at the moment of opening. The performance is that the gate has not been separated from the valve seat, and the valve stem is broken at the root of the upper or lower thread. The reason is usually considered to be a stuck gate, which is actually only part of the reason or a secondary reason. An important reason is the abnormal pressure increase after the valve body cavity is closed, that is, after the valve is closed, the fluid pressure in the cavity enclosed between the upstream and downstream sides of the sealing surface is much higher than the upstream pressure. There are two reasons for this phenomenon. The fluid in one of the middle chambers is heated by the upstream fluid to heat up and expand, causing the pressure to rise sharply. When the second gate is closed, the fluid is closed in the middle cavity and cannot flow out. The middle cavity space is further squeezed by the valve stem. Because the compressibility of the liquid is very limited, the pressure will also increase sharply. This phenomenon is especially likely to occur in power plants. On the feedwater gate valve. At the same time, its abnormal boost pressure will generally increase in a geometric progression, far exceeding the design limit of valve stem strength. |
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