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Failure Analysis and Treatment of Stainless Steel Bellows and Globe Valves


Failure Analysis and Treatment of Stainless Steel Bellows and Globe Valves

The following three aspects will tell you about the failure analysis and treatment of stainless steel bellows and globe valves:
1. The stainless steel bellows globe valve is installed on the pipeline of the ship’s power plant. During use, the valve has problems such as leakage at the valve stem and rust of the valve stem, although it has been repaired. But the problem recurs. After analyzing the cause of the failure, an appropriate solution was taken to eliminate the failure and ensure the performance of the valve.

2. Problem analysis

The leakage of stainless steel bellows globe valve is generally divided into internal leakage and external leakage, and there are many reasons for leakage. Endocrine is generally caused by the fact that the liquid medium contains solid impurities that damage the sealing surface and cause failure. Combined with the analysis of the on-site use, the reasons for the leakage of the valve stem are mainly related to the valve structure, working environment and operation mode.

2.1 Structure The valve stem adopts a double sealing structure of bellows and packing. The bellows, the inner lining ring and the outer lining ring are welded into a bellows assembly, and then welded with the valve stem and the guide body to block the leakage of the medium through the valve stem. The up and down movement distance of the valve stem causes the flat key I to move upward until the upper end face of the flat key I contacts the lower end face of the lower packing. Since the lower packing is made of PTFE material, if the valve is opened too much, the flat key I will be embedded in the packing, the valve can no longer be opened and closed, and the bellows assembly will be killed, causing the medium to leak along the valve stem. The tensile length and compression amount of the bellows are determined according to the stroke of the valve. If the limit stretch or compression is exceeded, the bellows may be damaged, causing the small tube to rupture and the seal to fail. Therefore, it is necessary to increase the limit device for valve opening and closing, so that during the valve opening and closing process, the bellows has been expanding and contracting within the design range.

2.2 Working environment The harsh working environment of the bellows globe valve is also a cause of its failure.

Because the bellows globe valve installed in the hull works in the salt fog environment for a long time, and the upper part often drips with condensed water, which causes the upper thrust ball bearing to corrode, and in severe cases, leads to contact corrosion with the valve stem. Opening or closing the bellows globe valve may cause the valve to fail to meet the relevant performance requirements. When the valve is closed excessively, the sealing surface may be crushed, resulting in the failure of the sealing when the valve is used again. When the valve is opened too much, the bellows assembly may be operated, causing the valve to leak.

3. Improvement

After analyzing the problems existing in the valve, its structure, operation and environment have been improved. The first is to increase the limit welfare fee of the flat key I, and add a stainless steel packing pad with a thickness of 3 mm to the lower packing of the PTFE material to prevent the packing from becoming dirty and limit the valve stem.

When the valve is closed, if the valve cannot be closed, the valve should not be forced to close, but open the valve, flush it with fluid for a period of time, and then close it again. When the valve is opened, when the valve is opened to a certain height, after the valve stem encounters a small resistance, try not to continue to force it to open, so as to prolong the 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, try to avoid condensed water dripping directly on the valve port port, which would cause the valve stem to corrode.
The above is the fault analysis and treatment of stainless steel bellows and globe valve shared with you today. If it is helpful, please forward it to let more friends see it~


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