Steam discharge - Valve selection 1

[Valving]

Dear All,
I received a support request from a client of us. They live seat failure by the below application and valve,
Media : Steam
Temperature : 143 Degress C
Duty : On-off
Valve is generally in off position. The valve is opened when the system steam
pressure increase over a set pressure value and discharges the steam to the atmosphere.
Valve Type : V-port ball control valve.
It is located that max shutoff pressure of the valve is 275 psi thus the valve is facing some problems.
1.Which type of valve do you advice to use? (Eccentric plug control for example?)
2.Will triple eccentric butterfly valve be a good solution? My consideration for butterfly valve is the disc in the flow. Discharge speed of steam could decrease the life of the disc and sealing, I guess.
Pls. share your comments.

 

[rmw]

Does the valve open fully when the pressure reaches a set limit or does it open only a small amount proportional to the amount of over-pressure?

rmw

 

[Valving]

V-port ball valve was opening fully.
Important point is the use of triple ccentric valve.
Action could be altered by butterfly valve.
but you could share your comments
a.the disc is fully open
b.the disc is partly open.
Yes butterfly valves has applications by steam but I need to know the consequences.

 

[gerhardl]

At 143 deg C ((289 deg F) saturated steam will have a pressure of 4 bar or 58 PSI. If I read you correct the valve have a pressure rating of 275 PSI (about 18 bar).

Nothing in the given data should indicate that the valve as such is wrong. I have myself described and experienced used V-port ball-valves for steam for higer temperatures and pressures than the given.

Seat failure by steam indicates however strongly a number of possible, and regrettably relatively common faults:
- if soft sealing virgin teflon is used as seat selaing this might easily be too weak and damaged by overtemperature or exposed to uneven pressures/temperatures (see further comments below) even if temperature/pressure curve indicates that the seat material is OK.
- carbon reinforced teflon has far better properties for steam.
- if the valve is not properly shut or opened (just a tiny a crack opened), or seat already is partly damaged (or combinations of this) the steam will give drawing of the soft seat material and cavitation damages, especially if condensation is present.
- if metal seat, same causes could give the same type of damages starting from particels or scratches or tiny openings.
- unsatisfactorily drainage (missing or wrongly placed or equipped or wrong type of steam trap) might give condensation giving cause as above or worsening factors above.
- if automated opening of valve (or hand operating) wrong adjustment and unproper opening or closing may give causes as above.

A golden rule for steam applications is that if the steam piping is not properly dimensioned, laid out and drained for condensate and filtered for partickles problems will occur.

Conclusion:
If the valve else is properly constructed for the purpose, and the steam and pipelines free from particles and smudge (filter and steam trap before regulating valve), V-port should be OK.
Better would be a steam control seat valve.

Any good supplier of steamtraps and related equipment could advise you on type of valve and steamtraps and proper layot.

Any valve selected should be dimensioned for the steam amount, in such a way that the valve is not left regulating with too small part-opening.

Note: actual practise in operation and actual conditions on site could well vary from what you get reported.

Picture of the damaged seat could probaly tell a lot a long with picture of total application/layout.

 

[Valving]

Gerhardl,
I appreciate your extended comments.
The VPB is with flexible metal seat (Flexible 317 stainless steel with heat treated electroless nickel overlay, ASTM A240) and plant is a geothermal plant. I am at home right now and dont have the photo with me. But nearly 1/3 of the seat ring was sheared off.
We suspected that the heat treatment was not applied properly so the heat sheared off the ring but the vendor shared the comments I wrote in the 1st thread. (400 psi)
Actually I agree with your pressure statement, but I could not claim against the vendor.
Any I will send the photo asap but meanwhile I will appreciate your further comments.

 

[gerhardl]

If cavitation is causing the problem, the cavitation will leave clear visible tracks,( having seen it once you will not be in doubt): a wear surface very uneven, including pittings and placed around streaming path right downstream of of small openings.

With the damaged seat you will probably see this. It is unlikely that product material quality and production in itself is the cause of damage, but not impossible or excluded.

My guess is that the seat/valve has not been closed properly, or dirt or scale have cuased rifts in seat (hairline rifts could cause problems)or hindered proper seating and leaving a small crack. Damage by cavitation will then start from this and after a while be much larger than original crackopening starting the process.

Possible causes as stated in first posting: dirt,condensation,operational faults, adjustment (more than 95% of all cases) and finally product fault (less than 2% of all causes if valve else qualifies - numbers 'guesstimates')

If the valve was factory pressure tested, this in itself would ensure that product fault is the most unlikely cause, if the valve else is within process specifications.

Control of sealing properties for valves within steam processes with condensation or impurities will be best taken care of with a steam seat control valve, and again probably best if the seat is protected from the outflow by 'skirts' in the valve outlet and seat sealing in 'sunken' position (sunken between protecting rings).

In this case this valve will probably be a better solution, but the original valve should be OK if 'everything else' with the process is OK.

 

[Valving]

Gerhadl

Pls. find attached the photos. Maybe it could give better understanding.

http://files.engineering.com/getfil...a-d076-4dcb-b682-ee4939dce49f&file=photos.pdf

 

[gerhardl]

Are there any tracings of wear on pipeline downstream of valve (if any piping)? Have missing part of sealings been found?

Orientation of damages bottom of sealing, bottom of valve opening whereas v- port right or left?

Tracings on ballshell and damages indicates impurities gathered before valve, sticking to ballshell and sealing and giving damage to seat, and in all probabillity not damage starting at wrongly manufactured seal giving damage to ball.

Is this a drainage from a well or from lowpoint or bottom of a pipeline?

If yes, impurities and condensate will gather here and be forced across opening, and impureties stick to inner parts of ballshell and create problems.

Impurities or scales from pipeline seems anyway to have been present.

My 90% guess is unsatisfactorily drained and filtered pipeline before the valve with perhaps unfortunate layout and dimensining of components.

If impurities have to be flushed out at this point you should probably split the pipeline in two separate parts. One complete pressure control station and one point for flushing out dirt. (Last one with smaller more compact ballvalve (not v-port) and perhaps flushing out from bottom of y-filter).

Contact an expert for steam-pipeline layout and dimensioning and for control of steamtrap types and accessories nd correct applications. If my guess is correct the whole plant should be checked.

 

[JimCasey]

A star for Gerhardl! I have been otherwise occupied for a while but it is good to see that Gerhardl has maintained his brilliance.

I think you covered all the possibilities.
Cavitataion is unlikely but flashing is almost guaranteed if there is any condensate in the line before the valve opens. This would show up as erosion damage. Your comment about improper stream-trapping mirrored experiences I have had with isolation valves on steam lines.

The valve WILL have sonic velocity across the seats and the seat may have just been blown away. Also the noise when that valve opens will be significant

Another hint was Geothermal steam. Geothermal steam is Frequently a saturated solution of various minerals and laden with grit.

It would be worth investigating the velocity downstream of the valve. A larger diameter pipe downstream and an additional diffuser to reduce the pressure ratio/velocity in the valve, the velocity in the downstream pipe, and the noise generated would contribute to longer service life.

 

[Valving]

I dont have words to express my appreciation. I am working on this issue right now and will be back with the progress details.
Is it possible to clarify the valve type you mention with steam control valve?
Do you mean any valve with control duty or a globe valve?
Could you pls. clarify?

 

[gerhardl]

Thank you, JimCasey, and you are of course right with your precise comments on cavitation versus flashing (my fault)! Welcome back to the forum!

Valving: it is about as difficult to select a car for another person as selecting a valve if you do not have a 'more than complete information'.

I believe, as stated above, that this is a bit more than a valve problem, and that reconstruction and additional items (y-filter with smaller blowout ballvalve atached and float operated steamtrap at properly placed and constructed 'well' for condensate at least) are probably necessary, all properly dimensioned, in addition to an outlet/regulating valve (Outlet to free air or regulating pressure with excess to closed pipeline/system?).

Some indications:

http://www.tycoflowcontrol.com/valv...boiler_trim_valves/index.aspx?id=tcm:106-5008

http://www.gestra.de/gestra_usa/

http://www.spiraxsarco.com/products-services/browse-products.asp

Above companies are represented worldwide and have available information on selecting and dimensioning of valves and acessories.

Competitors exists of course!

Further extended direct advice on the complete installation will probably exceed what is sensible on a forum basis, but technical questions on single details are of course always welcome!

Good luck!

 

[Valving]

If you wanna see the application point, see the attached pdf file.
As you see the pipeline is horizontal but the discharge line to muffler is diagonal and muffler is highly elevated than the valve. I am just sharing in case you want to see the progress.

And some answers to my questions from the operater;

1.By operation, are you sure that VPB valve stays completely shut-off?
YES
3.Are there any steam traps or strainers before the valve ?
There are steam traps on the pipeline.
4.Is there any indication of flashing or cavitation?
As the steam line opens to atmosphere in the muffler, media could be jetting.
Hot water leaking from seperator could be flashing.
5.Are there any impurities by the line ?
There are no smudge butwhen water rising in the seperator flees to the steam line, they are carrying silica etc which tends to build-up.
6.Is there any condens collecting in the line?
Yes, steam traps could be clogged sometimes.
7.Do you realize any wear or pitting by the downstream piping?
We can not see the interior but when we check out from outside, there is not any wear out.
8.I am not wrong, when we visited in December, I was told that there is a noise by the operation of the valve.
When the valve is closed, steam tries to flee to the atmosphere with high spees, just like a pressure cooker.
9.IS the steam pure ?
It is water steam.

Wish you a nice weekend !

 

[JimCasey]

I had experience with sootblower valves (normally remain closed most of the time) The line was not trapped properly so when they opened the (globe-control) valves they were hit with high-speed slugs of water. These valves had pilot-balanced cage trim, but it could not balance as fast as a sonic slug of water changed the loading. The valve-stems were bent into an omega shape.

High-speed slug of water could have ripped the seat of your ball valve away, and the lost part of the seat corresponds almost exactly to the V-notch at about halfway open. If true, the operators would have noticed frightening noises and jumping of the valve when initialloy opening it. (steam Hammer)

It is vital to keep steam lines trapped so that they have NO pools of condensate. Not only does it protect from steam hammer, but it drastically limits thermal shock. If condensate pools on the inlet side of the valve it is possible for it to be as cold as ambient temperature.