- July 13, 2022
- 6:16 pm
- Comments
When it comes to industrial valves and fittings you always want the best material available, but this should not be the deciding factor because sometimes the unit is not right for your particular application. As a fluid systems engineer or plant manager you must know all the requirements of your system: the fluid, the temperature and pressure conditions, and various other factors must be considered.
It is important to choose valves and accessories made of the right materials. If you do your research before you buy, you can avoid potential failures. We must consider those parts of the valve that have direct contact with the fluid (wet areas) that will vary according to different types of valves.
Here’s the detail… The chemical incompatibility of materials and those contacts with each other that suffer an uncontrolled chemical reaction can cause emissions of toxic, corrosive or flammable gases.
It is also not about knowing the full range of compatible materials because it does not make any sense. The applications in the industry are too wide and our process is subject to very particular and specific conditions of each line that makes up our manufacturing product. However, it is always useful to have the basic data: type of fluid, concentration, temperature and pressure.
For example, if we need to select a material for the service of H2SO4 at 98% and a temperature of 120°C with a pressure of 70 PSI, the best recommended solution is a Teflon-lined diaphragm valve with a Teflon diaphragm, since it is applied at low pressures and its body can be covered with any thermoplastic, in this case, such as Teflon. Being a corrosive service, the coating manages to withstand a temperature of up to 150 °C and as it is a Class VI valve, it guarantees hermetic closure.
Also as a second option a Teflon lined gate valve can be installed. The only detail is the internal walls of the body at the moment of closing/opening the gate. The friction with the lateral walls of the body can rub and lose hermeticity.
In the particular case of corrosive applications, there is the possibility of implying a quite significant reduction in the cost of a valve, either between a selection of metallic valve lined in some soft non-metallic material such as PTFE, PFA, elastomer or another against one of special alloy such as Hastelloy, Titanium, SMO254 or other. While it is true that both work for the application, there is a cost/useful life relationship that can be projected, allowing for more than one alternative.
“Effective selection of a valve requires practical knowledge of the types of valves available on the market, available manufacturing materials, in addition to a deep knowledge of the process and behavior of the fluid that needs to be controlled. Generally, in this selection and specification process, many times they do not take into account all the necessary considerations to comply with the application requirements that could be classified as critical or severe, which ends in a deficient valve operation”.
There are other variables that also imply an analysis of material selection depending on the type of application: seal, seat, packing, gaskets, diaphragm, etc. And he always remembers: “There are no bad valves, no incorrect selection of materials”.
Source information:
- • Muñoz, M. (2014). Especificación de válvulas para aplicaciones críticas. Revista Electro Industria.
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