IMPORTANCE OF USING METAL SEATED BUTTERFLY VALVE IN HIGHER RATINGS

Metal seated butterfly valve are recommended to use in higher pressure rating like #300 and more rather than PTFE seated valve  .PTFE seated valves are designed for using in chemical industry and for low pressure rating and non critical applications and they are designed for class IV leakage only i..e permissible leakage as per API 598 were as metal seated valves are designed and destined to use for higher temperature ,critical application like – hydrocarbon, Sulphur fumes, steam, gases – nitrogen, oxygen, argon etc and they give stringent class VI leakage and highly preferred or can say are only recommend to use for refineries, petrochemical ,terminals , LNG,LPG etc.

As  described and explained in previous mail also PTFE seat valves are meant for low pressure rating and non-critical applications mainly for chemical , water sector  as they have leakage class IV and this amount of leakage is permitted in these non-critical sector and loss is also economical whereas metal seated valves are used for critical application and higher ratings from #150 and above were leakage rate is nonnegotiable and require only zero leakage to avoid expensive leakage loss and reaction of hazardous medium with the environment.

 So, as per our above discussion we request you to only use metal seated valves only for the Oil & Gas projects and this is not recommendation it is a requirement.

HYDRO TESTING OF VALVE AS PER API 598

   HYDRO TESTING OF VALVE AS PER API 598 

API 598 states that the hydro test pressure maximum is determined using yield strength. 

1. For body shall test pressure shall be 1.5 times the pressure rating . 

2. Where as for Disc seat Hydro test will be 1.1 times of the pressure rating. 

In Oil & Gas sector valves need to be tested as per API 598 standard only to be suitable for the stringent requirement in refinery sector. 

Testing valves at different pressure rating as per API 598 is as follows:-

 

Rating	Design pressure as per rating	Shell test pressure	Seat Test Pressure
PN10	10 bar	15 bar	11 bar
PN16	16 bar	24 bar	17.6 bar
#150	21 bar	32 bar	23 bar
#300	52 bar	78 bar	57.2 bar
#600	104 bar	156 bar	114.4 bar
#900	150 bar	22 5 bar	165 bar

 

• Shall test pressure on Body
• Seat test pressure on Disc 

As per the above table is was understood that as the rating increase design pressure also increase hence the shall test pressure and it is to be noted that soft seat will not sustain and will break away in the high pressure and are successful till pressure rating of #150 class only. As at #300 pressure rating i.e 52 bar design pressure  were the shall testing is required to be done at 78 bar which is itself a very high pressure, soft seating even PTFE will break up so , it was found that vendors to pass the valve, do shall testing at 1.1 times (i.e. 58 bar) on shall test in place of 1.5 times  (78 bar). Which is a very wrong practice and could lead to catastrophic accident in refineries and petrochemicals as due to sudden surge or break up valve disc seat will break up as soft seat is not designed to sustain and perform at such a high pressure , they are suitable only for normal pressure and medium like water mostly.

We are attaching the API 598 Table 2 & 3 illustrating the shall test and seat test pressure mark ups on the design pressure for your kind pursual and reference .

 We hope our above given justification will fulfill your requirement and will able you to take a right decision in betterment of project. 

Advantage of Long Pattern Design ROSOV over Short Pattern ROSOV in Tankage

 

Difference between Long pattern & short Pattern ROSOV 

 

• In petrochemical industry in tankages & terminals all designs are govern by API standards and flanges of valve  are design as per API 600 standard  ( which is a gate valve standard also )and it is to note that Long pattern of butterfly which is having same face to face of gate valve , its flanges are also design as per API 600 standard and during commissioning of valves for mating tank nozzle flanges which are also design as per API 600 standard there is a compatibility of mating both valve and nozzle flange of tank to assemble them with buts & bolts. Whereas short pattern flanges of Butterfly valves are design as per ISO standard and there is a compatibility issue in mating with the Nozzle flange of tank. Due to which there will be play in both flange mating resultant leakage of hydrocarbon which is very hazardous. 

• Also to note ,ROSOV are required for emergency closing of tank with a very less or minimum closing time of less than 5 to 3 second and due to quick closing there will be high surge in amount of pressure is exert on the valve disc ( this pressure which is total of pipe pressure and gravitational pressure which will exert more due to hight of tank as tank height which could be  around 9 meter). Due to certain surge in pressure on disc which has to be evenly distribute to the body of valve by the disc , long pattern body & disc will sustain such surge in pressure as due to long pattern body there will be pressure drop from the high surge decrease to normal were as there could be breakage in disc in short pattern as here valve body is smaller and could not sustain such high pressure  and disc has to absorb such high pressure and many times causes breakaways which could be very hazadours. 

• It is being observed there is a seating issue in short pattern as compare to long pattern valve because after certain time due to wear and tear and impingement effect seat would not be  proper amalgamation of seat and seal resultant leakage in valve after some time were as such issue is not observed in long pattern as long pattern body will nullify the impingement effect and valve will give zero leakage for the very long service life. 

• Also to note due to emergency closing there is a hammering effect in short pattern valve as due to backward surge in flow  pressure which causes due to flowing in back ward direction by fluid due to quick closing as there will will be less space for the fluid to flow and will flow back. Were as long pattern design nullify such hammering effect as their will be pressure drop in fluid flow due to long pattern as fluid has to cover more distance resultant pressure drop. 

Looking at such above points it is highly recommended to use long pattern in comparison to short pattern specially at the tank nozzle and aloo the tankage using companies -IOCL ,BPCL ,HCPL are using long pattern design only.

Advantage of Triple Offset Butterfly Valve Over Conventional On/Off Valves

ADVANTAGE OF TRIPLE OFFSET BUTTERFLY VALVE OVER CONVENTIONAL ON/OFF VALVES

Triple offset Butterfly valve ( which is also called metal seated due to 3rd offset in seating to incorporate metal seating to give zero leakage and tight shut off like rubber sealing) in place of gate , Ball valve , some of the examples given below are as follows:-

1. Replacement in tankages in all the marketing terminals of IOCL ,BPCL ,HPCL across india :- After HPCL Jaipur terminal fire in 2009 , MB Lal committee investigate the fire and gave recommendations (attached) to replace Gate valve and Hammer Blind Valve with metal seated Butterfly valve in ROSOV( Remote Operated Solenoid Valve and MOV (Motor operated Valve) operators .Resultant Metal seated Butterfly valve replaced gate, hammer blind valve in tankages of marketing terminals , since standard metal seated butterfly valve face to face is as per API 609 CAT.B Table 3 ( C) which is short face to face in comparison to Gate valve and to incorporate the short face to face butterfly valve fabrication fabrication of Hydrogen pipeline which itself is a risky and costly affair and also in many cases Blind flange to be mounted on other end of valve for future expansion of pipelines especially in new projects .But there were problems in using short face to face Butterfly valve because Disc will protrude the blind flange on moving it from its resting location . Due to which long pattern metal seated Butterfly valve ( as per API 609 CAT.B TABLE 3 (B) ) with a face to face similar to gate ,Ball valve is used to replace the gate ,ball valve etc in the marketing terminals specially in tankages .

2. Replacement in Fire water Line by Triple Offset Butterfly valve :- As we have seen generally red color fire water line across plants in Refineries, Power, steel sector , gate valve is generally used for the operation of pipe as rubber seated valves are not preferred as due to animosity of Indian weather conditions rubber ,PTFE seat use to get break away (pls refer to Annexure –VII attached) due to regular expansion and contraction from heat & cold conditions. Here also now Metal seated butterfly valve is replacing Gate,Ball valve as it is easier to operate with low to zero maintenance cost and cheaper due to use to less metal in comparison to gate valve. 

3. IBR Application :- We all know IBR valves are used is a very critical application for steam,Boiler ,Hot gases etc here valve has to perform in extreme high temperature & pressure conditions in rating from #150, #300 ,#600,#900 ,here gate valve is generally preferred to use , but now Triple Offset Butterfly valve which is also called quarter turn gate valve is used for the new projects and replacing the gate valve in older projects.

4. Control Valve :- Previously Globe ,ball valve was generally preferred to use in control valve application generally in fertilizer , Oil & gas sector but now metal seated butterfly valve with size selected on sizing calculation is considered to use in control valve even in critical application like – Hydrocarbons ,ammonia ,hot gas ext .( examples in Energy saving projects in IFFO -aonla,Phulpur ,Kalol – Triple offset Metal seated Butterfly valve with Pneumatic actuator and positioner is used to replace previously mounted ball valves in the Ammonia plant. ( Pls refer to Product capsule for 28”#300 – Control valve working since 2010 in Carin Bhogat terminal and refer the IFFCO kalol order of 18” #600 ). 

5. Suitable for higher sizes & ratings, Critical application :- Metal seated Butterfly valve is easily used in higher temperature upto 900 Degree C ,Rating #1500 – 260 bar and sizes upto 100 “ , we have already received the order of 88” from IOCL Paradip for Hot gas application ( refer to product capsule), Dangote refinery ( PO attached with GAD) for flare gas application and IOCL Gujarat – 76” Refer the PO),Sour Service ,Cryogenic application,Hydrogen application etc. 

6. Power sector – Ash line ,ACW ,DM Plant, Hydrogen cooler line here Triple Offset butterfly valve is now replacing Gate Valve in existing lines at Thermal Power plants in a large extent.