Manual ball valves for steam isolation

[rusty_sim]

Hi

The customer's maintenance engineer is requesting manual ball valves for manual steam isolation (double block and bleed). I have used gate and globe type (Spirax Bellows Seal) in the past with good result. I prefer ball valves as automatic steam isolations. Something like a Keystone KTM.

The idea of manual ball valves as steam isolations seems a bit strange to me. I have mentioned that the operating torque might be a bit high and ball valves are not meant to opened slowly, which is preferred on steam. We could use a geared hand wheel to help with manual handling, but are harder to find and reduce the compactness that makes ball valves great in the first place.

Maybe I need to be a bit more open minded

What's your thoughts?

Kind regards

 

[gerhardl]

Hello rusty sim,

You seem to have a good grip on possible valve problems.

My comment:
As valves for all other fluids, steam is all about size, pressure, pipeline layout, construction, application, quality and operation of the valves. (But for steam perhaps even more so.)

For smaller sizes and moderate pressures ball valves may well be a good and relatively cheap solution. Most problems with ball valves for steam are caused by not satisfactorily and soft seat sealings, which may be misformed by even minor leakages. Or, as you mention, they could cause water-hammer problems by not satisfactorily condensate drainage.

For all sizes and pressure steam valves you should be safe if you have a plant with correct condensate drainage, correct layout and correct (slow) opening and correct closing, disregarding type of valve. BUT: only by using valves constructed for the steam-pressure you are using, fabricated by renowned producers and designed for the application you have.

As known, incorrect layout and failing/missing condensate drainage causes more problems than different types of valves, if the valve in itself is suitable for the application.

Regrettably most steam plants will,at some point, have poor layout and misssing or incorrect/failing steamtraps.

Good luck!

 

[MFJewell]

What is the line size?

 

[rusty_sim]

Thanks for your reply gerhardl, you're correct that all valves will have problems without proper condensate separation and trapping. The valves are to be installed on shell and tube heaters (10 barg) with a single separator upstream. Lines will be taken off the top of the header etc.

MFJewell, the lines are probably 40-50 NB and valves will be ansi 150.

The manual valves would only be closed for maintenance of the heater or during commissioning. During operation steam flow to the heater would be controlled by an auto ball valve and globe control valve.

 

[MFJewell]

In my facility we have many manual ball valves that size. I would have to check if any are on steam lines (we do have automated ball valves that size on steam lines). I know the manual ball valves I have operated in that size move easy enough that they could be opened slowly if desired. Just make sure you use a quality valve and I don't think you would have an issue. Also instead of a gear reducer, you could just put a longer handle on to make them easier to operate.

 

[gerhardl]

Hi again!

With the long periods between operations, and then the additional requirement of no leakage over a long lifetime, I would personally, without doubt, have used a globevalve or angle valve. The ball valve will have higher risk of impurities damaging the sealings, and should anyway be test operated more often than a globevalve to ensure OK operation.

A high-quality ballvalve construction will minimize the risk, but the price would probably be higher without gaining much against a globevalve in lifetime and safe operation.be higher.

A thight-closing globevalve with 'skirt' or coned globe would be better than a standard globevalve.

 

[mk3223]

IMO, the ball valve with soft seat isn't suitable for the steam service, which may be easy to operate, but have the erosion or high temperature issues. Does the customer have an existing experience with the ball valve with the satisfaction result in operation?

 

[moltenmetal]

The "right" manual valve for steam isolation is the gate valve. It suffers from poor seating (they are typically class IV), but they are reliable and cheap, with comparatively few failure points. At 150# class, regular packing is fine- no need for bellows unless the steam is really contaminated water vapour from a process containing toxic or flammable materials.

They are difficult to actuate- by "difficult", I mean in the sense that they are unnecessarily difficult to actuate in the same way that it is unnecessarily difficult to drive screws with a hammer.

At 150# class, PEEK seated ball valves are generally the right solution for automated steam block service. They will give better service life and tighter sealing than a metal-seated ball valve, which along with perhaps the triple offset butterfly at larger sizes is likely what you'd need above 150# class.