Coker Valves 3

[dragos12]

I am trying to understand the major 2 solutions for coker line : ball and plug valves.
Beside licensor specs, does plant switch from ball to plug? Or they follow initial specs
which were prepared by the licensors?
It looks like biggest advantage of plug valve is inline maintenance capability.
F-F dimensions are same?Thanks in advance for your time.

 

[mk3223]

Why consider to use the valve different from the Spec, which has an advantage to the maintenance?
The same F-F dimension fo two different valves is not a only reason to swap them.

 

[dragos12]

As I investigated , earlier plug valve were used in coker plants. Then ball valves became more common.(why?)
Beside complex operation function of plug valve looks like weak point and 2 actuator requirement. (for turn and lifting)
So I try to understand why users began to prefer ball after a point and if there is a reason for a user
to replace ball valve with a plug.

 

[Danlap]

Old(er) plants used to implement what seemed good ideas at that time, name a few but not limited to: Plug valves (it was marketed as one of the best tight shut off valve), pressure seal (reduce some weight on piping compared to conventional B/B valve), Y-type globe valve (easier to operate/seal, etc.)
However, there are disclaimer in compensation for all of the above. Metal seated Plug valves usually lubricated hence periodical lubrication are required; pressure seal’s sealing plate/ring joint have fatigue lifetime and should be replaced after some years; and many others.
Please consider that this was the era where operator were generally allowed to be multi-tasking as well as have better sense of valve-ownership. Personal opinion, now we give those kind of tasks to subcontractor, external valve specialist, etc.
And throughout the years, it feels like we’re leaning to end user comfortable zone and change everything accordingly. My operator stop doing plug valves lubrication since 15++ years ago.

As long as there is no written feasibility report or risk analysis written from those days, it’s hard to justify what was inside our predecessors’ head when they select such valves. And can only compare both features apple to apple.
Metal seated lubricated plug valve vs metal seated ball valve:
Similarity:
Quarter turn vs quarter turn  comparable travel time and actuator

Difference:
Lubricated every xy months vs no lubrication
Internal leakage: tighter (with lubricant) vs less tighter (ball valve normatively starts to worn out after xy cycles). End user start to accept that internal leakage is not top priority?
Usually port size 70% vs full bore.
Friction and actuator sizing??

Regards,
MR

https://nosuchvalve.com

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376

 

[gerhardl]

Simplified this is a standard case of evaluating and compare an existing set of valves against another set of valves. What you want to find is the cheapest cost over time (cost per time unit). You can do this more or less complete and detailed, but you would want to consider some, or all/more, of a list of points:

buying cost
installment cost
dependability (expected running time without trouble or maintenance)
maintenance cost
valve availability (deliverytime)
spare(part) cost and availability
sparepart stocking cost
repair cost
standstill cost by unexpected and planned repair/maintenance
cost of operator unit (as this complete list if valve and operator is not a complete mounted unit)
other costs different for the two valve-choices...and so on.

As Danlap has commented: plug-valves today would probably be less available with longer deliverytime and a higher price. Standard plug valves, or even high priced special versions, for instance double eccentric plug valves, could however anyway be a sensible choice under circumstances (price over time!). However probably less so in your case.

 

[dragos12]

Thanks Danlap and Gerhardl for input.
So acc. to your experiences, you verify that ball valves are better than plug valves
for such dirty, high temp and high cycle operation like coker?

 

[Danlap]

I am not saying that ball valve is better than plug valves. Have repaired hundreds of ball valves but only overhauled a handful of plug valves for the last 20 years, it still not necessarily means plug valves are better than ball valves or vice versa.
Almost all manufacturers in Linkedin says they are the best BALL valve manufacturer and/or repair companies. This is also not necessarily true.
My 2 cents, not all service company can repair Plug valve, it would be a challenge to re-engineered damage trims for Plug valve due to very tight tolerance. Agree with Gerhardl, spare parts of Plug valve have a loooong delivery time and usually OEM specific.
Considering dirty process, high cycle and medium to high temperature. Subjectively speaking only a handful of ball valves’ vendor are quite good and can respond fairly within due time for support and/or replacement. Name a few Flowserve, Metso, MOGAS.
All types of valves will (start to) fail after xyz cycles. Shall proper maintenance and/or overhaul (with prepared spare parts) commenced before that period, then theoretically there shouldn’t be any problem with both valves. Subjectively speaking number of cycles for plug valves will be lesser than ball valve.
As an end user, often I am in favor for plug valve due to less headache in the long run, but my operator who has to grease it every now and then are not in agreement and our project manager who has to pay higher price (than ball valve) also do not agree. On second thought, I don’t really like the ideas to have limited supplier of plug valve.
Main advantage for using plug valves on dirty medium is that the Plug design would ‘help’ to sort of ‘scrap’ the dirt from stuck against the sealing area (read: sleeve/seat).
Problem with high temperature, often, thermal expansion among sealing components might jammed the movement. Risk for most quarter turn valves with tight tolerance.

Regards,
MR

https://nosuchvalve.com

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376

 

[gerhardl]

There is no absolute answer here. The best valve is the best valve for each single operation point's details. Valves for coking processes have, as any range of valves for special purposes, been improved over the years.

You must check the market and see what can be offered with long-term references at operation details similar to yours. The answer might also be other valve constructions depending on exact operation details.