Ball Valves vs Globe Valves

Dear Tornado, I don't think that we have to use globe valve on drain line, if that valve has to remain closed for considerable time and we have to open it only for maintenance purpose, then I think Ball valve should be the choice. Thats what i have seen on many process plants. Any further insights will be welcomed. Regards,

Thanks very much, any response no matter how off the cuff it is, is helpful!

With regards to the outside pipe diameter that I mentioned, that is the maximum I'm looking to go, so basically anything smaller than that is completely acceptable, bar going too small that the flow rates become unrealistic.

With regards to the valves, I was looking around online (not always advisable I know) and came across this valve:

Bonetti Bont HTB ball valve - http://www.bonetti-valves.com/B06-23_Catalog_Ball_Valves.pdf

, it seems very clever (using a graphite and metal compound seat) and although I know little about valves, this valve seems to stand out amongst all the others as being one of the more innovative valves.

You might be right. However, the sealing surfaces/elastomers in a ball valve are exposed to the high temperature, and might be sticky. In a globe valve, the sealing surfaces do not slide much, and are simply pulled away from their mating surface. The real working parts (stem threads) of a globe valve can be further removed from hot zones.

Ok so it seems that the jury is still out on which of the two vavles to use,

Tornado, I see that it shows you as a piping design engineer, in terms of this, I am also required to select an appropriate material for the pipe to be made from, so far I have these three options:

SA 217 WC9

SA 105

SA 182 F12

These materials seem to best fit the profile, and are also used in the valve body, so welding the valves to the pipes will be made easier from this. Which of these if any best suit the application? My mentor (who is now conveniently on leave) has suggested that I look at both forging and casting as an option for the valves, hence the materials above being mixed.

One final thing, I am struggling to find the temperature range which is considered high temperature, medium and low temperature, as 217*C water/steam is used for cooling purposes in a power station (500*C being the more common temperature). I ask this because in the ASME material section guide, the above materials are considered high temperature materials, so I am just wondering if I would be wasting them here.

Thanks for all the help so far!!

1. I strongly recommend to use globe valve only for the purpose intended. Gate valve & ball valve are not so suitable for de pressurisation at such a high pressure.

2. For boiler applications above 350*C is considered as high temp. Below 350*C is low or medium.

3. For high temp application only forged steel valve body is recommended. However, for below 350*C either cast or forged steel can be used.

4. For pipe material for intended application (low temp & high pressure), I have seen following materials in use:

SA 106 Gr B

SA 210 Gr A1

SA 192

Pritam

As per technology supplier's specs, up to 380°C, 38 bar pressure, A105 is suitable material for steam services, above 380°C up to 425°C and pressure 38bar, F12 or WC6 material is suitable, frorm 425°C to 520°C and pressure up to 105 BAR, you should look to WC9 or F21/F22 or alloys containing 2.25% Cr + 1% Mo or so. Your specs are typical of these range. Still as temperature is only 217°C and pressure is in range of 300bar, you can very well depend on any of A105 or F12. I will prefer A105 because of good workable material.

won't the packing[seal] on the stem be critical too?

I was taught that incoming flow should always be from over the seat, not under

the temp being somewhat dependent on the distance the valve is from the normal flow...

Hi Garhh,

I was taught that incoming flow should always be from over the seat, not under

This is not true my friend, dependent on the type of globe valve and pressures involved, the direction of flow can alter.All low pressure systems will have the flow coming from underneath the valve..........even up to 70kN, however temperature will have a bearing on this.

One of the positives, in flow coming from underneath the valve, is when the valve is shut, the gland is not under pressure.

All globe valves that I have dealt with in marine applications have all had the flow from underneath the valve. Another is, the resistance the valve creates to fluid flow, coming from under the seat, is equivalent to about 30m of straight pipe..........my guess is that it may be higher in the reverse direction of flow.

One of the positives, in flow coming from underneath the valve, is when the valve is shut, the gland is not under pressure.

You have it exactly right! For the 2 power plants I had experience in ALL the globe valves were installed so the high pressure side is from underneath. Having the gland isolated from the system has 2 major impacts... 1) if this is a normally closed valve (such as a vent or drain) the packing is isolated from the pressure which means you can repack the valve without shutting down any systems and 2) there is less of a chance of packing leakage because it is isolated.

if this is a normally closed valve (such as a vent or drain) the packing is isolated from the pressure which means you can repack the valve without shutting down any systems

You may like to do that, not this little black duck,and I do not teach any of my students to do that.............OH&S..........isolate and tag out is the safe way.

is less of a chance of packing leakage because it is isolated.

I never open a valve fully (except refrigeration valves). I fully open a valve and then back it back half a turn...........I have seen too many valves seize in the open position because of people doing that. Mind you, another reason that valves seize, is that valves are not moved through their full range of movement, at least once a month.

I've only repacked a valve under pressure a couple times (note it was my supervisors decision to have it done). You're right about the lockout/tagout. As funny as it might sound, the valves I have done using this method were tagged (and as I recall, handwheel removed). In both cases the downstream was vented to atmosphere. Repacking a valve under pressure really isn't a practice I would recommend either, but it can be done in a safe manner. Packing leaks typically can be lived with until the next outage/shutdown.

In regards to the standard valve ops, I must say I'm in complete agreement with you.

You're right, I was thinking of valves that are actuated indirectly

for smaller sizes of blow offs needle valves are useful to have maximum control over the rate of pressure drop...

...........and they can vary between long and short tapers as well..........the long tapers giving "infinite" control.

Typical short taper valve

Typical long taper valve

Garhh, these illustrations were not for you, but for those that don't know which way a "y" type strainer should be placed in the system.

I haven't worked with HP/HT steam, and don't off hand know the best pipe choices. Refrigeration uses a lot of A-105 or A-53B, and sometimes A-333-6 if really cold.

Tornado's input coincides with my experience (12 years at 2 power plants). Neither of these plants had ball valves in high temperature service. While I'm sure you could find a ball valve spec'd for these conditions, I've never seen one.

There is a possible misprint in my post 5. The refrigeration pipe might be A-106 instead of A-105. I don't have a code book at hand. This may be analogous to high-temp (A-515) vs low-temp (A-516) pressure vessel plates.

Hi,

As per me, it is better to use gate valve instead of ball valves. it is due to temp. Now days we get ball valves in the market which can be used in at high temp, but u have to go for metal seated ball valves and not the soft seated which are more costlier than the gate valve. aslo for draining puropose it is better to use gate valves.

Regarding the material, as Tonrando said ASTM A106 Gr B material is acceptable.

I was quite interested in this article. A question I have for the more knowledgeable is up to what steam pressure and temperature would you recommend soft seated ball valves?

Our max steam pressure is 12 bar/1200kPa. I have a thing about ball valves on any thing over 25mm/1".

dear sir,

I suggest you to go for forged steel globe valve with socket weld ends for the above service conditions,normally balls valves are not suitable for pressure relief applications under very high pressure.The ball valve req only quarter turn of handle operation of valve for closing(or)opening,but the globe valve req no of turns for the same operation.So pressure can be released in a globe valve is better than ball valve.More over ball valves are mostly available with soft seats with two/three pc constuction,which is not suitable for high pr and high temp applications

ELLURU RAMAIAH.

I've found this quite interesting, both the question and comments.

The parameters are on the 'edge' for 'special' ball valves, but within the capabilities of 'common' globe.

"On the edge" and 'special', tend to mean expensive and the tight QC essential, is not always there.

"Sexy" is not a good ranking factor with HP steam.

Perhaps not an "purely mechanical engineering" evaluation, more a 'reality engineering" set of choices.

GA Tornado post#1

I'm not sure if the "sexy" is intended for me, but I was talking about the idea, not how the valve physically looks. Anyways I'll be meeting with the maintenance guys in a couple of hours and they're going to give me their input, I'll put it on here for those interested. Tornado's first post though has done it for me, if feel from further research that a globe valve would be the most appropriate. I'll be back in a few hours, wish me luck!!

From what you say it looks almost like a blowdown valve.High pressure drop and high temperature.This could be a severe service valve

Take a look at this

http://www.yarway.com/hy-drop.asp

Hi srini,

I concur with your thoughts on this.

Although the temperature is not particularly high, the pressure is significant, which I think, makes it entirely unsuitable to use a ball valve as you have very little control over the pressure release (as pointed out in a previous comment 1/4 turn). A globe valve with external thread and bridge could also be used.

Just finished the meeting with the repair / maintenance guys, they seem to prefer the ball valves over the globe valves, but this is only specific to the area that I've been assigned to. The one guy says that for my drain line only being at about 220*C, that the ball valves have impressed, but any of the higher temperature boiler applications, all of the pins in the ball valves a breaking, so they're reverting back to the globe valves in those higher temperature applications.

I work for an oil refinery and we use mostly gate valves. They are good for high temp and press.They will also be cheaper. We use globe valves for throttling processes.Ball valves are higher maintence and over time they will not seal as well.

good luck

hi, In my opinion, gate valve should be avoid in this high pressure service, at hight different pressure, gate valve can be bind and if you try to open, the seal will be score and leak. I will choose globe valve for this case. Duong Trung

We do have that problem with slurry, but with steam blow-downs they work well. Globe valves are your better choice, but are a bit more expensive.

If this is a blowdown valve, one configuration I have seen in low-pressure steam is a globe valve in tandem with a lever-operated disc/gate valve. The lever-operated valve is fast-closing if need be, and the actual blowdown can consist of a full opening and closing of the globe valve, which takes some seconds or so.

The Yarway valve in one post was an intriguing concept that might be adaptable to certain refrigeration applications.

Have some points to share,

Actually the selection criterion depends on the Client/Project requirements but as a minimum we have....

-Gate valves are used in On/Off service. Least cost valves but we can not use them at High Temperature/High Pressure due to Thermal Binding problems associated with it.

-Ball valves are also good in On/Off provides bubble tight shut off. More costly than gate but we can't use them in depressurization at such High Pressure. For High temperatures one has to use metal seated ball valves.

-Globe valves are good for draining at such High P/T.

Please correct/add comments on the post to make it informative to many users.

Thanks!