Causes of aging and internal leakage of large diameter stop valve
The large-diameter stop valve is generally used at the boiler outlet, main sub cylinder, main steam pipe and other positions, which have the following problems:
1) Generally, the pressure difference at the outlet of the boiler is large, so the steam flow rate is larger, and the erosion damage effect on the sealing surface is larger. In addition, the boiler combustion efficiency can not be 100%, which will cause a large water content of steam at the outlet of the boiler, and it is easy to cause cavitation and cavitation damage to the valve sealing surface.
2) For the stop valve near the boiler outlet and the cylinder, because the steam just coming out of the boiler has intermittent overheating, in the process of saturation, if the boiler water softening treatment is not good, some acid and alkali substances will be separated out, which will cause corrosion and erosion to the sealing surface; There are also some crystallizable substances may adhere to the valve sealing surface crystallization, resulting in the valve can not be tightly sealed.
3) For the inlet and outlet valves of the cylinder, the steam consumption after the valve is large or small due to production requirements and other reasons. In the case of large flow rate change, it is easy to produce flash, cavitation and other phenomena, thus causing erosion, cavitation and other damage to the sealing surface of the valve.
4) Generally, when the large-diameter pipeline is opened, the pipeline needs to be preheated. In the preheating process, a very small flow of steam is generally required to pass through, so that the pipeline can be slowly and evenly heated to a certain degree before the stop valve can be fully opened, so as to avoid excessive expansion caused by rapid temperature rise of the pipeline and damage of some connecting parts. But in this process, the valve opening is often very small, resulting in the erosion rate is far greater than the normal use effect, seriously reducing the service life of the valve sealing surface.