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Reduced vs Full Port Ball Valve Class 600Helpful Member!(2) 

gatossi (Materials)
8 Jun 07 4:37
Good day! I have a question in regards to ball valves.
I just took over a project for a Process Plant and I'm checking the selection of valves. When I came to ball valves 600# our specification says to be "Reduced Bore" but our three vendors (all very well known and respected) had offered "Full Bore".
Is this standard for 600#?
Thanks for your help!
gerhardl (Mechanical)
8 Jun 07 4:59

Reduced bore is often cheaper to produce. Often used by producers and vendors to offer a cheaper solution,  especially for smaller sizes, but can be found for all.

Depending on pressure class, exact type and construction this is more a question on what is available, cheapest and best adapted to the technical conditions and total requirement.

Ask the suppliers for additional information, and why they offer this solution. Depending on the project status you could either check if 'reduced bore' is a technical requirement (probably not) - or you could recheck the whole piping system and see if the piping and valve sizing is optimized or could be reduced down to next dieameter.

Such specs are often 'leftovers' from previous projects, and need to be revised from time to time according to commercial availability of products and what is happening in the real world winky smile.

Helpful Member!  zdas04 (Mechanical)
8 Jun 07 7:09
When I started doing pipeline work, reduced bore valves were about 25% less expensive than full-bore valves.  About 5 years ago the supply and demand picture changed and valve manufacturers were being asked for a lot more full-bore valves than reduced bore valves.  Today you actually pay a premium for reduced bore valves with several suppliers.

I've never found a technical reason for installing reduced bore ball valves, the reason was always economic.  If the full bore valves are actually less expensive then there becomes zero reasons for using the reduced bore valves.

Finally, if you thing there is ever any possibility of running a smart pig in a line don't even consider reduced bore valves.  While cleaning pigs will usually traverse reduced bore valves (I saw one once in a 42-inch line that required 2 hours for the pig to deform itself enough to go through the first valve on a river crossing, then went through the valve at the other sided of the river in a few seconds--I don't think it did a very good job of cleaning under the river) smart pigs won't.

David
JLSeagull (Electrical)
8 Jun 07 7:36
I was unaware of the trend of pricing to equalize between reduced and full bore ball valves.

A few situations require the full bore valve besides pipeline pigs.  Examples also include low pressure compressor suctions.  This applies anywhere that additional pressure drop is a problem.  Full port valves are normally used where inserting sample probes, injection quills, etc.
Helpful Member!  JimCasey (Mechanical)
8 Jun 07 9:34
I pretty much observe the same trend: if the valve has to pass some sort of solid instrument (pig, quill, probe, hot-tap) then a full-bore is appropriate.  Whenever I have calculated the loss through a standard-port valve, the pressure drop seemed to start with a decimal and have a couple of zeros before a significant digit. So there's unlikely to be a pressure-drop reason to select a full-port valve.  Of course a full-port valve has no more loss than an equivalent length of pipe, and probably less since the bore of the ball is almost invariably smoother than the bore of the pipe.

Actuated regular port valves are significantly less expensive than full-port valves because the full-port valve requires more torque, thus a larger-more expensive actuator...
JLSeagull (Electrical)
8 Jun 07 13:25
Automated valves are normally my area of interest related to ball valves.
zdas04 (Mechanical)
8 Jun 07 15:22
JimCasey,
The point about the actuator is only true if you are desiging close to torque limits in very clean service.  In nasty service (which is all I ever see) I typicilly use a safety factor of about 3, so going to full port reduces that safety factor to about 2.9 with the same actuator, no big deal.

David

David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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Ashereng (Petroleum)
11 Jun 07 0:21
Most vendors will offer the valve you specified, unless they don't have one. That is my industry's norm.

A full port is what I like because a) we often pig through many of our lines, and b) it induces less pressure loss than reduced port. If my vendor has dealt with me often enough, they know this and will assume that I either mis-typed, or got a junior guy to do the datasheet who doesn't know my preference.

A reduced port valve usually requires lower torque to close, in the same ANSI class. This is a saving on the actuator, in addition to the cost of the valve.

Without more info, it is tough to say why your vendor has done this.

"Do not worry about your problems with mathematics, I assure you mine are far greater."   
Albert Einstein
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MortenA (Petroleum)
11 Jun 07 6:30
Ashereng

Given zdas04 argument re. the normal safety factor to full bore valves dosnt it then sound like "conservatism" that we (my self included) still allmost by defaul specify reduced bore - and offers some time to specify exactly those valves that need to be FB? Maybe it would be cheaper to say: All below size XX ==FB (unless specified)?

Best regards

Morten
JimCasey (Mechanical)
11 Jun 07 9:13
David, I agree that you can't have too much actuator.  I took a look at my torque tables and that torque comes really close to doubling with every size increment.  So your actuator safety factor does not drop from 3 to 2.9 when you compare a regular port to a full-bore valve, but more like 1.5. (Bigger actuator required)
JLSeagull (Electrical)
11 Jun 07 12:19
Use a safety factor.  ZDAS04 uses a larger safety factor than me.  I also specify a pressure regulator set at the minimum air pressure and require the actuator selection based upon that pressure with the safety factor.  Watch for options such as graphoil packing that increase the torque.
Ashereng (Petroleum)
11 Jun 07 17:30
Hi Morten,

I do not exactly understand your question - would you post it differently again.

In the mean time, I will explain a bit more what I meant.

With regards to safety factor, I usually add about 25% to the required torque, and then find the actuator that can do the job. For a reduced port or full port, the percentage increase is the same - hence, there is still an actuator savings in price.

Like David has mentioned, my preference is for full port ball valves, as it serves the purpose most often in my industry. Again, this is a personal preference.

Hope that clarifies my earlier response.

"Do not worry about your problems with mathematics, I assure you mine are far greater."   
Albert Einstein
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zdas04 (Mechanical)
11 Jun 07 21:09
I use a very large safety factor because the first time I used a 25% factor, I had a stuck 16-inch valve that was really expensive to get fixed.  When we pulled it we could see that the insides of the valve were coated with a mixture of coal and parafin that was just too sticky for the torque tables.  I was just really lucky that it failed on an ESD test and not on an ESD situation.  I've been a real chicken ever since--small savings in valves and actuators can be dwarfed by the cost of process upsets.

I just looked up the last actuator I bought and the safety factor was 2, not 3.  I may have been waxing poetic above.

David
JLSeagull (Electrical)
12 Jun 07 10:07
An oversized actuator is not a big issue for small line sizes.  However as you move into the 36 NPS and larger area you begin running out of spring opposed piston actuators that will work with 80 psig air if your safety factor is excessive.
Sircrashalot (Mechanical)
12 Jun 07 14:07
Another issue with large SF is that you will often come up against the MAST of the valve.  My client's specs will usually only allow me to go to 90% of MAST.  One client also needs 2x SF at all points of the torque curve, which on a 150# valve can lead to a SF of 6 or even more at the break point with the 'correctly' sized actuator.  If the valve manufacturer has been conservative and given only a 5x SF to the MAST, I'm not in a good place.  Gets to be a tricky point finding the right actuator for the job.  And the client wouldn't let me tinker with the relief or reg set points either.

Reduced port valves in 'made to order' exotic materials (F51, titanium etc.) will still be cheaper, however commodity type carbon steel valves with 316 trim would be more readily stocked as full port as in a pinch, most client's either need a full port or they don't really care. This is likely driving the production of the full port valves and thus a reduction in cost.

Andy
Scotsinst (Petroleum)
13 Jun 07 11:19
I agree that FB versus RB is totally an economic issue.
FB are only required for compressor inlet (or similar), PRV inlet/outlet or a line to be pigged or probed, as mentioned by others.
It is not good economic practice to blindly use FB valves regardless of cost.  Remember, an engineer can do for a dollar what any idiot could do for five.
I cannot think of any application where a FB cannot be provided instead of a RB.  Some manufacturer's do not make RB for small valve sizes.
The actuator sizing issue is very interesting because the cost impact is potentially huge.
Most customers of ours list a 130-150% actuator sizing margin although there is potential for David's experience.  Would it be prudent to use 130-150% for clean service (i.e. gas or clean liquid) and 200% for dirty service (i.e. oil with BS&B)?  I suppose it depends on experience with specific processes.
Donald
JLSeagull (Electrical)
13 Jun 07 12:31
A contractor might use different safety factors  -- smaller for lump sum projects and larger for reimbursible projects.
zdas04 (Mechanical)
13 Jun 07 18:46
Scotsinst,
JLSeagull's cynicism aside, experience in the particular service is truly key to properly spec-ing an actuator.  In clean, dry, gas with an operating dP significantly less than the design dP (i.e., for an ANSI 150 valve, the maximum dP is probably around 280 psig, but many 150 ANSI systems have a normal operating pressure closer to 100 psig, so operating a shut valve with normal pressure on one side and vented on the other results in 100 psid instead of 280) you will almost always be fine with 110%, but change any of the parameters and you could be in trouble.

David
MortenA (Petroleum)
14 Jun 07 1:31
Adhereng - sorry i misunderstood you.

Best regards

Morten
caihui (Mechanical)
14 Jun 07 6:05
Hi Gagossi, I don't think it's for money. I think is for your specification. As I'm a sales man. Always the specification say API 6D but in RFQ need reduced bore. As sales reduce bore is cheaper and easy can got the order, everybody knows that. So, please check your specification.
Hoping I'm not wrong.
gatossi (Materials)
14 Jun 07 6:17
caihui,
Sorry to say this time you are wrong... at least in respect with the spec...

We specify (bearing in mind this spec is 8 years old!) BS5351 Ball Valves Reduced Bore 600#.

I don't have any objection with full bore valves for this application (process plant... no pigging, no probe going trough, etc.. only shut on-off valve) but I got three different offers for a Full Bore valve (from three different manufacturers) and I was wondering whether the "standard practice" had changed (and so should my specification) or it was more an economical issue.


I thank you all guys for your answers (it was much more than I expected, as I also learnt/refreshed some other things beside my question)
Ashereng (Petroleum)
14 Jun 07 15:55
Morten,

No worries.

"Do not worry about your problems with mathematics, I assure you mine are far greater."   
Albert Einstein
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