Ball Valve is one of the most utilized types of valves in process industries and is widely used in tight shut off application. It is mostly used in quick opening applications like Shut-Off or Line Break type Valves.
Thanks to the use of non-metallic sealing materials, This type of valve has the capability of being designed for leakage class VI. Here is a place where engineers are facing with different sealing materials used for two portions of the valve: Seat sealing and Stem sealing.
The stem sealing materials are mostly Elastomeric non-metallics like NBR, HNBR, FKM, FFKM, VMQ and FVMQ. They are usually known by their trade mark names such as VITON, CHEMRAZ, etc.
Normally, when the valve operation temperature is below 220 C you can think about Elastomerics, otehewise they should not be used and normally the valve stem sealing technic shall be changed into another way to use graphite packing materials.
Take care of using Elastomerics as stem sealing on fully welded line break valves.
VITON may be used as the most well known Elastomeric while care shall be taken when it's going to be used in steam services. CHEMRAZ shall be preferred even for temperatures lower than 180 C.
Seat sealing ring is another application of non-metallics in ball valves and this time Thermoplastics are used more. The most utilized grades are PTFE, RPTFE, PCTFE, FEP, PFA, POLYAMIDE and POLYETHER KETONE.
The most utilized and applicable grade here is PTFE or RPTFE which is in the Fluoro Polymers family. Other members of the family are PCTFE, PFA, FEP and PVDF. The use of this family shall be avoided in Fluorine service. Another important notification in using them is to consider their limit temperature in different chemicals. For example their temperature limit in Sulfuric acid is 130 C while in Hydrochloric acid it is 150 C. A reference in this regard is SHELL DEP 30.10.02.13.
POLYETHER KETONE is also another wear resistant and mechanically high performance seat seal material. Albeit it shall be noted that its high temperature performance is not enough. There are two trade names known for that and they are PEEK and TURCITE and between them TURCILE shall be selected for applications up to 250 C.
