Leakage and Metal Seated Ball Valves 3

[cmcbain]

I recently inherited engineering responsibility for a poorly performing test assembly. The performance issues all result from a 4", 600#, Metal Seat, Floating Ball Valve that is intended to serve as a hydrostatic test boundary.

For background: I've attached a line diagram of my test assembly, all composed of 4" stainless steel piping. The purpose of the test assembly is to allow for testing of a relief valve (shown in the bottom right corner of the line diagram). The relief valve is overpressure protection on a steam system, so the test assembly is really just there to contain the steam.
During installation, a hydrostatic test is required to verify that there is no leakage at any of the flanged joints in the test assembly. The ball valve serves as the hydrostaic test boundary.

The problem: In my line of work, every component in every system has to be approved for use. The currently approved ball valve is, frankly, junk. A new valve will support anywhere from 1-10 hydrostatic tests before its leak rate becomes so excessive that it's impossible to achieve the required test pressure. Based on my research into how we ended up with this particular valve, it appears that a predecessor essentially purchased a valve recommended by a valve manufacturer with very little technical justification to back up the recommendation.
I'm trying to find out if I'm experiencing is just a fact of life with ball valves, or if I could find something better.

The Current Valve: Has the following characteristics.
4" IPS, 600#, Floating Ball
Body: 300 Series Stainless (2 Piece Body)
Ball: Ferralium 255 (not sure if its just a deposited coating, or if the entire ball is Ferralium)
Seats: Ferralium 255
The valve is made by a large and well known manufacturer, but it's considered a legacy product line, so I'm not getting very much engineering support.

The System: My working fluid is water, with a couple quirks. For reasons I can't control, there ends up being a small amount of high salinity water in the piping before the hydrostatic test. Even after filling the system with Deionized water for the test, the end product is probably water that has a higher than normal chloride content. There could also be any number of corrosion products or impurities in that small amount of water, meaning abrasives could end up deposited on valve sealing surfaces.
The hydrostatic test is performed at room temperature, but the valve will obviously become very hot during the use of the test assembly, as a result of the steam from the relief valve. I'd say up to 600 F.

In order to accomplish the hydrostatic test, I don't need a bubble tight valve. I do need a valve that minimizes leakage, and that can "seat" at a very low differential pressure/flow rate. My hydrostatic test pump can deliver < 300 cc/min, so I can't generate much differential pressure if there's a lot of leak-by to start out with.

I guess after providing all this background info, my questions are these:
1) Am I right in thinking a floating seat valve was never a good choice for this application? Seems like my puny test pump may not have the oomph to move a floating valve into place against a downstream seat.
2) Is it feasible to maintain a low leak rate through aobut 100 open-shut cycles of a metal seated valve? That's the number I'm shooting for, which would increase the number of test I can do to a maximum of about 25.
3) For those in the know, how do you feel that Ferralium 255 stacks up against the alternatives in terms of corrosion and abrasion resistance? The alternatives I see on most valve manufacturers brochures are various hardening procedures (Boronizing, Nobelizing), Inconel Alloys, Tungsten Carbide Coatings, and Full Ceramic valves/seats.

McBain

 

[LittleInch]

cmcbain,

first well done for a comprehensive post and diagram.

Can you confirm what operations and at what pressure / flow this valve opens and closes? It appears to be 4 times per test, but I'm not clear whether there is pressure and/or flow during any of these operations? It makes quite a difference so would be good to know.

Are these metal seats confirmed as only metal seats, i.e. no "inserts" or "lip seals" made from anything else?

I'm not sure how much you know about valves so apologies if you already know this, but a 4" #600 floating ball is not common - many vendors stop at 2 or 2 1/2" for floating ball. In part this is due to the large forces exerted on the seat - I calculated about 8 tonnes at rated pressure - hence any dirt or grit can become embedded in the seat or ball and if you operate it at any decent pressure then it just gouges a groove in the ball.

Have you ever taken any of the failed valves apart to see what the damage is? Pictures would be great. Have you sent any back to be repaired? Any feedback from the vendors?

your questions,

1) Yes, you are correct. A ball valve in any form is fundamentally unsuited to operation under pressure to open or close especially with hard particles present in the fluid. A plug, globe or even a gate valve would be more suited to this application. A floating ball does need some flow / pressure to start to make the seat "work" so this could be an issue, especially if you are getting leakage.
2) It should be if you get the right sort of valve or change the operation so it doesn't open / close under differential pressure or flow
3) I'm not sufficiently in the know so can't help, but you have a fairly high operating temperature so the harder materials may not be suitable.



My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[moltenmetal]

Metal seated ball valves are rarely bidirectional sealing, but they do tend to have floating rather than trunnion-mounted balls.

You might get better than class IV shutoff from a metal seated ball valve for a few cycles, but not over the long term in our experience. Count on class IV, or pick a different design. A 2nd block (low temperature, soft seated) with a bleeder between, or perhaps a trunnion mounted ball valve with a bleeder on the cavity, might do the job for you.

 

[cmcbain]

LittleInch,

I used 4 open-shut cycles for 1 test, but that is conservative and based on potentially having to do some un-anticipated operations. Ideally the valve is only opened and shut 1 time each. All open-shut operations are done at 0 pressure and 0 flow.

Let me provide a scenario for use. First, keep in mind that the entire "test assembly", which consists of everything downstream of the relief valve in the diagram up to and including the collection container, is only installed while we test the relief valve. Also keep in mind that the only purpose for the valve is to provide something to press up against during the hydrostatic test of the assembly.
The procedure goes like this:
-Connect the entire test assembly downstream of the relief valve
-Shut the Ball valve (at 0 pressure or flow)
-Fill the test assembly with water (through a separate fill port not associated with the ball valve) in preparation for the hydrostatic test
-Perform the hydrostatic test to check for leaks in the flanged joints in the test assembly
-Depressurize the assembly and open the ball valve
-Actuate the relief valve, discharges water/steam and any trapped impurities, through the system and into the collection container

To simplify the discussion, the valve is Manufactured by Noble Alloy. The product line is System II. It used to be pretty easy to find documentation for these via Google, but it looks like FlowServ is steadily erasing old brochures and such. I have attached a couple pages of a 10 year old brochure for the valves.
The metal seats are confirmed metal only. We have disassembled several of these valves and there are no soft parts in the ball seats.
I did not know that a 4" floating valve is not common. I've seen other discussions on this forum where people talk about using floating valves in sizes up to 6" or more, but I do notice that everyone tends to rate trunnion valves as a little more trustworthy in those sizes.

As far as disassembly or vendor contact, here's what I've got: We started out maybe 15-20 years ago with a 17-4PH ball and seats, same valve design. The valves would either be DOA, or would leak excessively after 1 use. We sent the DOA valves back to the vendor and they theorized that chlorides were attacking the 17-4PH and causing excessive corrosion. That's when the vendor recommended we upgrade to Ferralium 255.
After using the Ferralium 255 for a few times, it appeared that we were getting a pretty reliable valve. Then, several years ago, we started getting valves that were bad straight out of the box again, or that would work only once and then leak like a showerhead.
The most striking example I have is: I purchased a valve in January of this year. When we received it we performed a pre-use hydrostatic test to the same criteria as the vendor to make sure it wasn't bad. It passed the test perfectly. Then, I put it back in its crate for 8 months. When I recently tried to use it, it leaked so badly I couldn't raise pressure above static. Somehow, just wetting the valve 1 time (with deionized water!), pressurizing it, and opening and shutting it a couple times at 0 pressure, was enough to ruin the valve when combined with the 8 months of storage in a wood crate inside a heated building.


I feel semi-inclined to purchase a trunnion valve, based on all I've read. However, it feels like I might just be experimenting with little to no actual confidence that a trunnion valve would solve my problem. I'm not even sure what my problem is. There doesn't appear to be any significant corrosion, pitting, scratches, etc. so I'm just going with the theory that I have the wrong equipment for the job I'm trying to accomplish.

One thing I'm curious about is whether or not you HAVE to bleed a trunnion valve? Is the body of the valve not rated to the fluid pressure? Do you have to bleed the valve when it is open and shut, or just when shut?

 

[cmcbain]

moltenmetal,
Are you saying that trunnion valves are not common in a completely metal seated variety? Metal seats with polymer backups or o-rings don't work for me because while the relief test is going on, the steam is going to heat my valve hot enough to melt any polymers.
Since the purpose of my valve is a hydrostatic test boundary, not isolation to do work or disconnect any portion of the downstream system, double block and bleed doesn't do much for me. The leakage that bleeds by is still leakage from my hydrostatic test. If there's as much of it as I'm currently getting, I still can't do the test.
A downstream soft seated valve also doesn't do much for me. It would definitely help me accomplish the hydrostatic test, but I'd have to remove it from the system before discharging steam from the relief valve. In that case, I might as well just install something like a spectacle flange instead of using a ball valve. The benefit of the ball valve is that I don't have to do any connections/disconnections on the system after the hydrostatic test. All I need to do is open the valve.

 

[LittleInch]

I couldn't open the first of your attachments, but I get the drift. Seems like you've had a really bad time with these and it's difficult from a distance to see precisely where your problem lies. The only thing I didn't ask was what orientation you use the vales in - horizontal through or vertical?

you do see 4" floating ball valves, but at #600 they are less common.

I can't really comment on the spec / coating, but I think you will be much better off with a trunnion mounted valve. No the body bleed doesn't have to be bled and yes the body is rated to full class rating. The bleed (if used) is just to see whether the upstream seat is holding or not. For your uni directional purpose it makes little sense.

If I was you I would get a metal seated trunnion mounted valve with a Single piston effect (SPE) metal only seal on the pressure side and a Double piston effect (DPE) seal on the discharge side. It makes it a uni directional valve but gives you two seals more or less for the price of one. The trunnion should hold the ball in a much better position and with sprung seats it should seal with no differential pressure across it. Ball valve are still vulnerable to damage from particles when opening, but you should get a much better life from those than what you have at present. you need to talk to a couple of valve vendors and see if any inserts can now withstand the tmeperatures you have as moltenmetal has a point - metal seats are not good for repeated high class sealing and some sort of soft seat insert will make your life a lot better.


My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[cmcbain]

Valve is on a horizontal piping run.

Is there any good literature out there on the different flavors of Trunnion Valves? I have only the vaguest understanding of double piston effect vs single piston effect and I'd like to educate myself.

I also definitely need to educate myself, or get some vendors to educate me, on the capabilities of the different ball/seat materials and coatings. I keep wishing that there was a table out there like the elastomer chemical compatibility table that would give me a good/better/best rating for working fluid and temperature compatibility with the different ball and seat materials.

Got any recommendations on valve vendors with metal seat experience? One of the downsides of public employment is that I have to warn every company that I talk to that any purchase goes to contract and that I can't control who gets the contract. Doesn't exactly make people want to bend over backwards to help me when they realize they would have to bid on a contract to sell me a valve.

 

[MikeHalloran]

One comment: DI water is extremely corrosive.

Regular tap water has a lot of 'contaminants' that collectively tend to stabilize, or 'buffer', the water's pH.
Whereas, deionized water contains no natural buffers, and the local pH can be easily driven up or down, producing localized corrosion cells.

... or something like that. My point is, from a corrosion perspective, you'd be better off wetting a new valve with almost anything other than DI water, e.g., pond water, rain water, tap water, automotive coolant, salad dressing, whatever.

How about using, instead of DI water, the chemically treated/stabilized water that's typically used as boiler feedwater?






Mike Halloran
Pembroke Pines, FL, USA

 

[cmcbain]

Mike,
This is actually a pretty obvious point that I hadn't really thought about yet. Shame on me. After our 17-4PH debacle, I think everyone has been focused mainly on avoiding chlorides as much as possible. DI water is good for that, but you're right, the very fact that it's deionized probably means that it's got plenty of room for new ions to migrate from the surrounding material.

As far as receipt testing of the valves that we purchase, I'll definitely find a better fluid to use (salad dressing sounds like the best option). That might alleviate the problems I'm having with testing a valve once, storing it, and then finding that it's unusable a few months later.

While the valve is in-service (on the test assembly) it is pretty much guaranteed to be exposed to DI water or something close to it. That's just an unfortunate side effect of working in my industry. Still, now that I know better at least I can make sure the valve manufacturer is aware that I'm not just using tap water. I suppose Monel valve parts might alleviate both chloride and other corrosion concerns, but it may also be more susceptible to abrasion than things like Ferralium?

 

[MikeHalloran]

If you're only getting four cycles out of a valve, abrasion resistance may not be a primary concern.

Galling might be. Maybe your supplier can recommend a tribologically complementary alloy for seats or ball. I'm assuming that neutron radiation is not an issue for a test rig, so some copper content could be tolerated.



Mike Halloran
Pembroke Pines, FL, USA

 

[LittleInch]

There's a lot of literature out there, but whether it's good or not is a matter of opinion... do a search on this site and look up some big vendors websites, they often have a guide on what the basic functions are. Basically SPE seals in one direction, DPE seals in both directions.

I just did a quick search on high temperature ball valve seals and it looks like you're into metal seals or some sort of graphite seal at 600F. Most elastomers seem to stop at about 220C / 450F.

Not many valve suppliers will expect you to single source, what you need to do is get clever at the tender and either pre qualify those who can supply what you want or have a technical acceptance criteria part of your tender or a select tender list. You need to persuade the tendering dept that what you're after is something special, not your standard valve offered by any company. The key is in the data sheet and specification and that's in your hands.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[moltenmetal]

Everybody in the ball valve business is trying to migrate up-market. There are now a plethora of people who make run-of-the-mill ball valves who are trying to sell metal seated ones. Some are just cheating with metal powder-filled Teflon seats or the like, which they stretch the temperature limits of to get the order and then happily take orders for replacement seats when they're needed.

At 600 F and any significant pressure, you're full-on into metal seats.

We rarely buy trunnions of any kind. But if you think about it, because the ball can't move, a trunnion relies entirely on a spring to force the seat against the ball to make the seal. The sealing forces required of metal seated valves make that a hell of a big spring. Instead, most go with a floating ball design so the force of the upstream pressure is used to load the downstream seat.

My suggestion is to look into companies that have made metal seated ball valves for a long time. Or, consider a different valve design- why exactly does it have to be a ball valve? Or design around the leakage- when you're hydrotesting, you don't have the high temperature- that gives you options.

A couple suggestions of competent manufacturers for your exotic material metal seated ball valve, in no particular order. Some you've clearly already been in contact with:

1) Gosco
2) Noble Alloy Valve
3) TBV (now part of Cameron I think)
4) Valvetechnologies
5) Orbit- looks like a ball valve, but is something completely different

As to having a simple list of temperature, pressure and seal materials- beyond 600 F you're into custom designed for purpose territory. There is no cookbook. Coatings etc. are a black art and their success or failure is highly application specific. But if you're looking for reliable class VI shutoff for hundreds of cycles, my suggestion is just to give up now. All valves leak- you need to design around that rather than trying to pretend that someone can stop it from ever happening.

 

[LittleInch]

moltenmetal,

I'm afraid I'm going to have to completely disagree with your statement "a trunnion relies entirely on a spring to force the seat against the ball to make the seal"

The spring in a trunnion mounted valve seal simply holds the seat to the face of the valve during rotation and when there is no or low differential pressure. The sealing force comes from the fluid forcing the seat against the ball face. If you look at any explanation of trunnion mounted ball valves you will find this. As an example look at the attached, page 13 which explains it better than I can. In the reverse direction, the pressure required to push a SPE seat off the ball from locked in internal pressure is often no more than 2-3 bar more than the upstream pressure, which is why these seats are often call self relieving seats.

As said, another benefit of the trunnion mounted is that you can have DPE seals on the downstream side so that any leakage into the ball from the upstream seat results in this seal working to seal the downstream face. Floating ball valves by definition only seat on the downstream side.

The load from a floating ball onto the seat, especially high pressure is huge, which is why you don't see then at large diameter (much above 6") or high pressure (many are #300 or less).

The rest of your post I agree with - 600F is beyond most seal materials so you're into exotic materials and metal seats will always leak - just depends how much...

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[donf]

cmcbain,

I second LittleInch's compliment on your communication skills.

I agree that metal seats are indicated. Have you considered a Y-pattern globe valve? From the conditions you've listed. that would be my first choice.

As Mike Halloran pointed out, DI water can be agressive. Do you have a handy source of Steam Condensate to use as the test fluid?

Regards,

donf

 

[moltenmetal]

LittleInch: I stand corrected- again, trunnions aren't something we see much of here.

Looking at the drawing in the link you posted, the separate seal on the OD of the seat that allows the seat to slide back and forth in the body under the "piston effect" (I.e. the force of pressure difference between upstream pressure and cavity pressure acting on the back side of the upstream seat, the force that I'd missed) is something that is difficult when you're at a temperature where elastomers aren't permitted. In a sliding ball design, that seal is a very different animal.

 

[cmcbain]

Wow, lot's of info and questions.

Activation is not a concern, so any amount of copper is acceptable. I haven't seen any evidence of galling on the balls or seats of the valves, but after reading that SealWeld white paper on the size of surface defect needed to cause a leak in a ball valve (linked on one of the other ball valve leak threads), it may be that the galling is smaller and more localized than what I'm looking for, and is still causing the leaks.

The first thing I need to do is establish a good relationship with a supplier, or multiple suppliers. Part of the problem is that we've just been re-purchasing the same product from the same vendor over the last 15 years. The vendor hardly knows who we are or what we're doing with their valve because we've just been handing them purchase orders, not communicating with them (don't get me started on why). The contract spec is completly bogus. It has 0 technical characteristics, just a manufacturer part number. That's one of the things I'm working on fixing.

moltenmetal: you got a little fired up there at the end of your post, but thanks for the good info. I know exactly what you mean about every manufacturer trying to up-migrate. Seems like every single company has tacked a sentence to the end of their product brochure along the lines of, "If you want us to, we'll throw some metal seats in anything!" I have indeed been looking at most of the manufacturers you listed, but I wasn't aware of Orbit Valves. That is a very cool design.

I am using a ball valve because of flow losses. The test assembly was originally designed with no valve. Then someone realized that there was no way to perform the required pre-use hydro test. At that point, the designer realized that the addition of a globe valve would screw up the test because it would create extra backpressure downstream of the relief valve that we're testing, changing the way the relief valve reseats during the test. From my research, even a gate valve would probably create too much extra flow loss. The Cv for the average full port gate valve is nearly half that of my ball valve.

The hydro test is done at low temp, but that's just a pre-use test of the installed test assembly piping to make sure there are no leaks. After the hydro we open the relief valve. That's where the high temperatures come from. If I have to remove the ball valve so it isn't exposed to high temperatures, it kind of defeats the purpose.

I don't necessarily need reliable CL IV shutoff for 100's of cycles, but what is a reasonable number of cycles. There some number of times that the valve can be operated and still maintain a low leak rate. Why even make a CL IV category if it's only good for 1-2 cycles of the valve?

 

[MikeHalloran]

If the ball is always full open when the steam hits it, then soft seats might be viable.

I.e., if the steam flow lasts only for a few seconds, or if you can cool the exterior of the valve, the seal area might not reach a temperature that is destructive to soft seals. ... or it might. ... but you can model or test the hypothesis.





Mike Halloran
Pembroke Pines, FL, USA

 

[moltenmetal]

Class VI shutoff for hundreds of cycles in an exotic alloy at these temperatures is not a realistic goal in my opinion. Vendors will claim class V - some may even claim class IV- but they won't achieve it without lubricants unless the service is very, very clean. In a corrosive service? Very doubtful indeed. Class IV for hundreds of cycles IS a realistic objective. But look at the leakage rate of class IV: it's quite high.

If your continuous service temperature isn't really 600 F but something even 50 F lower, or there is exposure only when the relief valve is open and it isn't open often or for long, you might get away with PEEK seats and have a hope. With hard metal seating you're going to have to compromise- or perhaps you can get away with the Orbit valve, if they make it in your materials which is not a certainty.

The setup puzzles me. Why exactly are you hydrotesting the discharge side of a relief valve? If you were testing the relief valve itself to make sure its crack pressure was correct and ensure that it wasn't leaking when closed, I would understand, but your set-up puzzles me as sketched.

 

[cmcbain]

Ok, 1 more question before everyone drifts away:

1) I saw a couple blurbs somewhere about trunnion valves being better suited to vertical piping runs than horziontal. Not sure why that would be, but can anyone confirm/deny?

BTW, Mike: You have a point about short duration. My application isn't exactly short duration, more like 1-3 minutes, but I am curious about whether PEEK might be up to the task.

 

[cmcbain]

moltenmetal,
Funny that we both posted about PEEK at the same time.

My bad, I meant that I don't necessarily need Class VI, but accidentally typed Class IV. What do you think about Class V? Realistic?

As to why I'm hydro'ing downstream of the relief: It's just a pre-use test of the piping that I've connected to make sure that it won't leak when we open the relief valve. All that piping is temporarily installed for the 1 day that it takes us to make sure the relief valve still works, and then disconnected again. If you're curious why I'm that concerned about leaks, accept the mystery