Non Suitability of PTFE Seal Valves in Fire Water Line

Non Suitability of PTFE Seal  Valves in fire water line :-

PTFE is (Poly tetrafluroetylene ) seal valves are considered as soft seating valves were PTFE is made from glass filled nylon or carbon filled nylon with a hardness of 50 HRC. It is consider as a memory loss polymer which when deforms does not retains its original shape.

 Now days Dual seating valves are available which are having two seating wherein one is PTFE and other is metal seating  and are claiming to be  Fire safe Design as per API 607 . Please note as per fire safe design API 607 which states that in fire condition valve should give atleast class V or worse class IV leakage which is permissible. In Dual seating  PTFE Butterfly valve design were there are two seating first seating is of PTFE and secondary is of metallic seating . This design is conceive  on the basis that as in fire PTFE which is rubber will burn out and secondary sealing will come in its place and will give tight sealing. But originally during fire when PTFE seating burn out and metal seating has to come in its place .Design is such that PTFE which is a primary seat is covering whole seating area and after it gets burn out  in fire conditions  and metal will not come in is position due to thermal expansion cause by fire  with temperature of 550 degrees and hence even on tight closing of valve leakage will be there which is below class III even PTFE which melts in the line will cause valve to get jam and hence not workable were as metal seating butterfly valve will work freely in fire conditions.

 Due to this reason PTFE valves are not considered as fire safe valves but only considered to operate in fire , hence metal seating valves is only considered as a perfect fire safe valve which can give class V leakage i.e bubble tight leakage even some of the design are giving zero leakage in fire conditions. Resulting for fire water line which is used to operate in fire conditions mainly metal seating valves are favored. They are tried, tested in this conditions in comparison to PTFE valves . the refineries ,petrochemical plants, fertilizer plants are using metal seating butterfly valve only  for fire water line. In the past generally gate valve was used in fire water line , now metal seating butterfly valve which is also called as quarter turn gate valve waiving off all the bottlenecks and problems arising like cavities, high maintenance requirement and cost even cheaper than gate valve in every aspect from initial cost to maintenance cost ,life cycle cost and even the operator cost as less torque is required in metal seating butterfly valve in comparison to gate valve and hence cost of operator like gear box , actuator will be less. IOCL ,BPCL ,HPCL ,EIL are fully recommending and using metal seating butterfly valve in fire water line.

This is also to be noted and understand that in water line rubber seated valves are used  which are much cheaper then PTFE and metal seated valves, but they are not used in fire water line because in fire rubber will get melt and valve will be free also due to melt rubber valves will be jammed and non workable resultant in-spite of these valves more suitable for water lines are not used fire water line.