Issues with the valve’s service life?
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Basic information: The working medium at the site is pure water (soft water), and the pressure is not high, at 0.8 MPa. The pipe diameters range from DN25 to DN150; therefore, the selection of valves is relatively simple, as most valves can suffice for these conditions. However, the pipelines in this area are quite important, and the valves may remain in an open position for long periods of time, without being operated or used, for several years – for example, 3 to 5 years, or even 10 years in some cases. Therefore, after a few years, when the valve is used, it may no longer function! For example, some time ago, during maintenance work, we tried to close the valve in that area (which had been in use for 16 years). As a result, all the branch pipe valves (of domestic manufacture) were damaged and could not be closed properly, causing internal leakage; it is likely that the valve discs or seals were damaged. It was only after closing the main pipeline valve (which was imported from Japan back then) that it was sealed off. Question: In situations like this, what are some good recommendations regarding valve selection? (This location is quite important; it’s not possible to replace the valve in regular circumstances.) Do you have any suggestions? What kind of valves will still function properly after several years? For our valves this time, there are several types depending on the operating conditions, such as ball valves and gate valves. Ball valves are made of stainless steel, while gate valves are made of carbon steel; however, their seals are made of cemented carbide, such as Z41Y-16C. There are now ANSI standard valves, which seem to be used more in the petrochemical and nuclear power industries. The structure of ANSI standard valves differs from that of national standard valves; are ANSI standard valves better? Welcome everyone to the discussion!
Reply to 1# up7u: Valves come in different standards such as Chinese, American, and European standards, but this only refers to the differences in the execution standards for valves; it does not mean that valves made to American standards are necessarily of better quality. The main factors affecting the quality of valves are issues such as the valve material, manufacturing quality, and the precision of the sealing surfaces. In situations like the one you described, where the operating conditions are fairly ordinary and such scenarios are common in the petrochemical industry, the problems that arise are generally similar. Therefore, these issues can be addressed from two perspectives: 1. Since water corrodes both the sealing surface of the valve disc and the packing, the valve disc and valve stem are prone to corrosion and detachment, which leads to poor performance of the valve. Additionally, corrosion of the valve disc’s sealing surface can result in poor sealing and internal leakage. It is recommended to use valves made of stainless steel, including for both the valve body’s sealing surfaces and the valve disc, in order to prevent rust. 2. If cost savings are desired, and ordinary gate valves are used, dual-valve control can be adopted for regular opening, closing, or replacement.
The quality of domestic valves is indeed substandard. In situations like those described on the first floor, minor leaks can be addressed by installing blind flanges after closing the valves on the various branch pipes. However, this approach isn’t feasible when dealing with highly hazardous materials. It’s hoped that domestic valve manufacturers will improve the quality of their products.
It is sufficient to choose ball valves from manufacturers with a quality guarantee.
Those valves are relatively cheap, so just replace them. Generally, the service life of the internal components of valves is around three to five years; it is therefore recommended to replace them regularly.
If a valve doesn’t operate for several years, it is prone to breaking. If better sealing is required, it is recommended to use a ball valve; when the system is not in use, operate it several times. (Note that the valve must be made of stainless steel, preferably 316 grade), as this may yield better results. After all, the valve contains lubricant, and if it is not used for an extended period of time, that lubricant loses its effectiveness.
The key is to use them; even valves that don’t need to be operated on a regular basis should be turned on and off periodically to assess any changes in their performance. This should become a system. It’s unrealistic to expect something to work right away after not being used for a long time. Of course, what was said above makes sense as well; when purchasing valves, it is necessary to choose the appropriate material and a reliable manufacturer. If the valve will not be in use for several years, it is recommended to choose a hard-sealed valve; otherwise, the service life of the soft-sealing material is limited.
This post was last edited by up7u on 2011-9-22 at 17:33. It seems that the people who commented above do make a point; the key is still to maintain and use it, taking some action from time to time! Our operating conditions are such that the system runs for 24 hours once it is put into operation, with a major overhaul taking place after more than a decade; of course, regular planned maintenance also takes place for about 24 hours each quarter. The key point is that during maintenance, this is a valve used for water-cooled equipment; unless there is a problem, no one operates it (sometimes it cannot be operated either – not even during maintenance, as the equipment will get damaged if the water supply is cut off). It also cannot be replaced under normal circumstances. That’s why the above situation occurs!
If you don’t mind the cost of valves, it is recommended to use stainless steel ball valves. Based on what you’ve described, the valves are mainly used in the main pipelines for water softening. Given such working conditions, and based on experience, these valves are of domestic manufacture, and they can function properly for 10–15 years without any issues.
The difference between American standards and Chinese standards lies merely in the standards themselves. The issue mentioned by the original poster is explained in detail on the first floor; personally, I recommend hard-sealed ball valves as a better choice!
Use it in conjunction with manual valves!