Fault Analysis and Handling of Stop Valves and Stainless Steel Bellows
The stainless steel corrugated pipe globe valve was installed on the pipeline of the ship's power plant. During use, the valve experienced problems such as leakage and rust at the valve stem, which have been repaired. But problems recur. After analyzing the cause of the malfunction, appropriate solutions were adopted to eliminate the malfunction and ensure the performance of the valve.
2. Problem analysis
The leakage of stainless steel corrugated pipe globe valves is generally divided into two situations: internal leakage and external leakage, and there are many reasons for leakage. Endocrinology is generally caused by the failure of sealing surfaces due to the presence of solid impurities in liquid media. Based on the analysis of on-site usage, the main reasons for valve stem leakage are related to the valve structure, working environment, and operating methods.
2.1. The structural valve stem adopts a double sealing structure of corrugated pipe and packing. The corrugated pipe is welded with the inner and outer lining rings to form a corrugated pipe component, and then welded with the valve stem and guide body to prevent the medium from leaking outward through the valve stem. The movement distance of the valve stem up and down is that the flat key I moves upwards until the upper end face of the flat key I contacts the lower end face of the lower packing. Due to the PTFE material used for the lower packing, if the valve is excessively opened, it will cause the flat key I to be embedded in the packing, making it impossible for the valve to open and close, and causing damage to the bellows component, resulting in medium leakage along the valve stem. The stretching length and compression amount of the corrugated pipe are determined based on the stroke of the valve. If the limit stretching or compression is exceeded, it may damage the corrugated pipe, causing the small braided pipe to break and seal to fail. Therefore, it is necessary to add limit devices for valve opening and closing, so that during the valve opening and closing process, the bellows will always expand and contract within the design range.
2.2. The harsh working environment of the bellows globe valve is also a cause of its failure. Due to the long-term operation of the corrugated pipe globe valve installed in the ship in a salt spray environment, and the frequent dripping of condensate from the upper part, the upper thrust ball bearing is corroded, and in severe cases, it can lead to contact corrosion with the valve stem
2.3. If the bellows globe valve is excessively opened or closed during use, it may result in the valve not meeting the relevant performance requirements. When the valve is excessively closed, it is possible to damage the sealing surface, leading to sealing failure when the valve is used again. When the valve is excessively opened, it may operate the bellows component, causing valve leakage.
3. Improvement
After analyzing the problems with the valve, improvements were made to its structure, operation, and environment. Firstly, increase the limit welfare fee for flat key I, and add a 3mm thick stainless steel packing pad to the PTFE material's lower packing to prevent the packing from getting dirty and limiting the valve stem. When the valve is closed, if the valve cannot be intercepted, it should not be forcefully closed. Instead, the valve should be opened, washed with fluid for a period of time, and then closed again. If it still cannot be closed, the grinding sealing surface should be checked. When the valve is opened to a certain height and the valve stem encounters small resistance, try not to continue forced opening to extend the service life of the valve stem and its sealing components. When installing a globe valve with a thrust ball bearing on the upper part of the valve stem, it is important to avoid condensation water dripping directly onto the valve's household registration, which may cause corrosion of the valve stem.
4 Conclusion
After the improvement of the bellows stop valve, there was no further occurrence of bellows cracking or valve stem rust
2. Problem analysis
The leakage of stainless steel corrugated pipe globe valves is generally divided into two situations: internal leakage and external leakage, and there are many reasons for leakage. Endocrinology is generally caused by the failure of sealing surfaces due to the presence of solid impurities in liquid media. Based on the analysis of on-site usage, the main reasons for valve stem leakage are related to the valve structure, working environment, and operating methods.
2.1. The structural valve stem adopts a double sealing structure of corrugated pipe and packing. The corrugated pipe is welded with the inner and outer lining rings to form a corrugated pipe component, and then welded with the valve stem and guide body to prevent the medium from leaking outward through the valve stem. The movement distance of the valve stem up and down is that the flat key I moves upwards until the upper end face of the flat key I contacts the lower end face of the lower packing. Due to the PTFE material used for the lower packing, if the valve is excessively opened, it will cause the flat key I to be embedded in the packing, making it impossible for the valve to open and close, and causing damage to the bellows component, resulting in medium leakage along the valve stem. The stretching length and compression amount of the corrugated pipe are determined based on the stroke of the valve. If the limit stretching or compression is exceeded, it may damage the corrugated pipe, causing the small braided pipe to break and seal to fail. Therefore, it is necessary to add limit devices for valve opening and closing, so that during the valve opening and closing process, the bellows will always expand and contract within the design range.
2.2. The harsh working environment of the bellows globe valve is also a cause of its failure. Due to the long-term operation of the corrugated pipe globe valve installed in the ship in a salt spray environment, and the frequent dripping of condensate from the upper part, the upper thrust ball bearing is corroded, and in severe cases, it can lead to contact corrosion with the valve stem
2.3. If the bellows globe valve is excessively opened or closed during use, it may result in the valve not meeting the relevant performance requirements. When the valve is excessively closed, it is possible to damage the sealing surface, leading to sealing failure when the valve is used again. When the valve is excessively opened, it may operate the bellows component, causing valve leakage.
3. Improvement
After analyzing the problems with the valve, improvements were made to its structure, operation, and environment. Firstly, increase the limit welfare fee for flat key I, and add a 3mm thick stainless steel packing pad to the PTFE material's lower packing to prevent the packing from getting dirty and limiting the valve stem. When the valve is closed, if the valve cannot be intercepted, it should not be forcefully closed. Instead, the valve should be opened, washed with fluid for a period of time, and then closed again. If it still cannot be closed, the grinding sealing surface should be checked. When the valve is opened to a certain height and the valve stem encounters small resistance, try not to continue forced opening to extend the service life of the valve stem and its sealing components. When installing a globe valve with a thrust ball bearing on the upper part of the valve stem, it is important to avoid condensation water dripping directly onto the valve's household registration, which may cause corrosion of the valve stem.
4 Conclusion
After the improvement of the bellows stop valve, there was no further occurrence of bellows cracking or valve stem rust
