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.

Case Study of Using 3 way control valve at Cooling water Station At Essar Refinery ,Jamnagar

CASE STUDY AT ESSAR REFINERY – JAMNAGAR

After the visit to cooling plant and the 3 way control valve of  FOUR’ S we had found that you had used pump valve discharge valve with ebonite lining . In this regard we proposes and recommend you to use two set of valve one Dual Plate Check valve (i.e NRV) with ASTM 439 GR. D2 Body casting & Duplex 4 A Plates and internals which are dually suitable for sea water application and the other one is Triple Eccentric Butterfly Valve with similar Material of Construction i.e Duplex 4A.We have supplied similar valves to your refinery in initial years when ABB LUUMMUS were setting up your refinery. These configuration of valves and material of construction is useful to avoid any damage to any stage for sea water application.

As we have noticed that Your velocity ie. 3.49m/s  for flow rate of 8000m3/hr. in the discharge line  which still being on higher side  due to which  all kind of lining are susceptible to failure and breakdown.

Advantage of Lugged Over Flange End Connection in Butterfly Valves

LUG IS BETTER THAN DOUBLE FLANGE END CONNECTION

Lugged end connections are better than flange connections in Triple offset butterfly valve in critical application due to the following reasons:-

•  In critical application like LPG gas where medium is susceptible to react to atmospheric air a valve with compact design is required which prevents medium from any leakage ,due to this requirement lugged is more preferred than double flange. As per seen in below diagram one long stud is inserted from one end of pipe flange which passes through hole of valve body end connection and then passes through other flange end of pipe and are tightened through bolts atboth the ends which tightens the grip of valve with pipe flange and prevents it from loosening in comparison to double flange design where flanges at both the end of valve, mate with pipe flanges at both ends with small nuts and bolts tightening separately , but as per API 609 CAT.B Face to face of Double Flange is more than lugged design which result in more weight in valve and more pressure on nuts and bolts in hanging and containing the weight of valve due to which after some time due to wear and tear and expansion and contraction due to medium and atmospheric conditions nuts start getting loosen up hence start leakage insides of valve and this leakage of medium could be catastrophic if it is critical and susceptible to oxygen due to this double flange is more favorable in bigger sizes and water application.

•  Big advantage of lug in comparison to double flange is after commissioning and execution during maintenance of valve and pipe, pipe can be easily opened from one side without removing the valve and valve will remain attached with the other end of pipe flange and there is no need to remove the valve and realigning it.

Advantage of Retainer less design over Retainer in Dual Plate Check Valve

Advantage of Retainer less Design over Retainer 

1.       In Dual Plate Check Valve Retainer Design, the center pin (Off which the disc rotate) and the limiter bar (which prevents the disc from hitting each other) need to be affixed in the valve body which results in a penetration through the body wall. In retainerless design, a sleeve is inserted into the inside of the body thus avoiding penetrating the body wall thus no hole to be made in the body resultant, no leakage after wards due to increase in size of hole from normal wear and tear.

2.       In Dual Plate Check Valve Retainer Design, hole is made to accommodate hinge pin/stop pin there is chances of leakage path in body in retainerless no changes as hinge pin /stop pin will supported by lock screw and pin holder inserted in cavity made in retainerless design to accommodate them inside the valve body.

3.       In Dual Plate Check Valve Retainer Design, stop pin/Hinge Pin can come out from the body from the hole were a s in retainerless design it is not possible.

4.       In Dual Plate Check Valve Retainer Design has limitations to be used upto 52 bars only were retainerless design is suitable to use in higher pressure rating like more than 600 bars.

5.       Retainerless design can with stand higher temperature and pressure conditions like in critical Hydrocarbon and Chemical processing applications, or any service where environmental safety or fire hazards are concerned were as in retainer design in higher temperature & pressure conditions there will be metal expansion in hole threaded area in the body could cause to hazardous issues of danger of reaction of fluid with the atmospheric air which can resultant lead to  fire hazards and leakage of poisonous gases in the environment due to leakage of inflammable and poisonous fluid & gases.

6.       In Dual Plate Check Valve Retainer Design in Flanged Model to accommodate retainer, a hole is puncture in the flanged which is not acceptable as per the standard API 594 and ANSI 16.5, were as in retainer less design there is no puncturing of hole in flanges hence design is acceptable as per the standard.  

PNID -Ideal Distance Between Pump & Valves

Ideal length PNID distance between Pump and valves

The problem of dis-alignment of pump from its present position is generally observed due to bad design in PNID which didn’t allow the medium to settle down and create unwanted pressure in the line and hence dis-alignment of pump and other accessories.

Given below is the typical pump station layout with valves at proper distance

Above given diagram is the ideal PNID describing the required distance valves should have from pump . Check valve should be at least 5 D distance from pump to absorb impact of surge and have enough time to close the valve plates with decreasing pressure of medium to prevent vacuum. 

Butterfly valve is used for opening and closing the valve and should be at least 3D distance from check valve. If check valve is less than 5D distance from pump than on closing of pump check valve will close and due to less distance to travel in pipe resultant qty of medium will be more and hence more pressure will create which moves back ward and form surge which will move in reverse direction and put pressure on pump due to which pump will get jerks due to back pressure and it will move from its present position. If there is distance of at least 5D between pump and check valve on closing the pump , due to large distance between pump and valve possibility of forming back pressure will get reduced and hence decrease in risk of back surge on pump.