With the use of different valves sold at https://www.kplokusa.com/ and having worked on various project in the past, I can say that several piping engineers usually stereotype the term severe service on the requirements of the valve.
In a particular system or process, few of the valves which are present can be considered as such and they are the ones which you will pass through a great challenge in the design. Each of the kind of valve which is of many types has several features which you need to consider.
These features will be discussed in relation to the double block and bleed valves because there are various valves and each one of them have features which is specific to them:
One of the features which is very common to steam service and power generation is high temperature and the rating of temperature which is required range from 400 C° to even up to 800 C°. Because of this, you do not need to provide special attention when it comes to the selection of material and design which goes in line with the allowable thermal stress.
It is also crucial to consider the general standard which is provided by the general body regulating the appliances, the working pressure relative to the temperature should be considered as well. There are some standard connections which also have their own limitations as well as ratings. As a result of the inherent limitation of some materials which are non-metallic, it becomes very common to find a temperature application which has metal-to-metal seated valves.
The corrosion is inevitable in most of the process industry but the application is much more in the oil and gas service applications. Hydrogen sulphide as well as other substance which are corrosive can be measured but the industry can only reduce the corrosion in a piping system.
There are some nickel alloys which are resistant to corrosion and can be used for corrosive applications as well as environments. Cladding as well as weld overlays on the valves have now become the order of the day in the industry and are mostly used for larger applications.
“Atmospheric Sealing” which is a special kind of design is introduced to the offshore market; corrosion is prevented from the outer environment in this case. For instance, a common problem which occurs in the Middle East is Chloride Induced Stress cracking. Apart from that, the high salt content in the sea water can affect the severe corrosion outside the body of the valve as well as sealing elements.
This factor has to do with the rate of flow of the fluid, pressure drop as well as turbulence which can hasten the erosion. However, a double block and bleed valve can be used for an isolation, opening and shutting the flow of fluid but what usually cause problem is abrasive media.
Abrasive media can result to a stretches on the spherical ball as well as the typical soft inserts. Immediately these scratches are magnified from the closing and opening operations, it would lead to a costly leakage which can also be hazardous. For this kind of application, a metal-to-metal seated isolation valve is perfect. Apart from the application of hard-facing like Chromium Carbide, Tungsten Carbide, as well as Stellite are the methods which is used in the industry because they are resistant to wear. You should also note that it is essential to select the appropriate kind of double block and bleed valve so as to have the desired result.
Those in charge of the management as well as operation of plants are aware of the valve performance, for installation in the industry, it is essential for the data sheet as well as the operating parameters to be reviewed and also compared against the actual or the experienced-based data. Once this is done, the appropriate valve would be designed for the application.