Welding of flanged valves

[airfox2000]

Hi All,

We've got a little exotic problem. We are installing flanged butterfly valves,as per clients spec., into an existing district heating system. Design is according to DIN / EN standards, pipe sizes DN500 to DN800.

Now the client wants us to weld the pipes directly onto the flange faces of the valves in order to eliminate the gaskets. This contradicts all rules of practice I know but I have not managed to find any standard actually prohibiting this practice. I would appreciate any info or links regarding this matter.

Thanks

Michael

 

[Montemayor]

airfox2000:

I wouldn't do it without doing the necessary calculations to prove the welding on the flanges will safely take the loading stress. You don't explain about the flange bolts: are they in or out? I assume, since you are welding the flanges' outer circumference that you will plug and weld the bolt holes. There is no reason to believe that bolting up the flanges will stop any leaks through the bolt holes. Or, does your client also suggest seal welding up both sides of the bolted joints since leakage is such a high priority? This is only logical and in line with the importance that your client is giving to leakage.

We don't know the line size or number of flange bolts involved, but as you can see this is starting to approach a ridiculous situation -- and only so so because your client is insisting to use a simple, conventional joint in an entirely different manner. There is no standard that I know of prohibiting what is suggested - just common sense. I would caution the client about the welding stresses and the cost of doing all this work with the end result of having a fixed valve unavailable for inspection or maintenance and ruined for all future applications.

We don't know the fluid and the priority placed on the leakage question, but it seems that a weld-design butterfly would be the preferable, cost-effective answer.

Art Montemayor
Spring, TX

 

[makeup]

The thing is, if something goes wrong with the valve or something in the vacinity when the investigating body looks at your connection methods who will put there hand up to take the blame. You have not used the product(valve) in accordance with the design. Now you are right, there probably wont be any documentation prohibiting your clients method and at the end of the day, if that is what he wants, make sure that it is well documented and you are not on the receiving end of any litigation and let him have it.

 

[zdas04]

I know this is off topic, but why are they not specifying a welded-in valve?

David

 

[corrosionman]

I also have an off topic comment;- make sure that the pipe inside dia is larger than the i.d. of the butterfly diaghpram or you might find that it will contact and prevent the valve from fully opening. You might need great care in positioning the pipe central with the flange for same reason.

But, replying to the oroginal question, the pipe will certainly be a different type of steel from the valve so you have dissimilar metal corrosion situation. with a flanged joint you have a gasket which substantially eliminates the problem.

And you need a sizeable excavation under the pipe for your Welder, and his Inspector, and possibly your Insurance Assessor too. Cheers David W

 

[donf]

If I understand your post, you're not trying to weld the mating flanges. The client actually wants to "weld the pipes directly onto the flange faces" .

If this is true, Art's comment concerning loading stresses is even more pertinent. There's also welding geometry issues, seat distortion potential, and the list goes on.

Contact the valve manufacturer. Explain what you want to do and ask if the warranty or performance of the valve would be affected. I know of no credible valve manufacturer that would endorse what's being proposed.

As I see it you have two options:

1. Specify and properly install high integrity gasket/bolting.
2. Exchange the flanged valves for weld end valves.

Actually I have seen a document that addresses this situation. It also covers things like "when ordering pipe, specify that the I.D. is to be smaller than the O.D...."

Seriously, we understand that clients are the source of our income, but please remember that we have a professional obligation.

Regards,
Donf

 

[airfox2000]

Dear All,

Thanks for your helpful responses. I would like to answer some of the queries raised.

1. Bolts will be out because they intend to weld a matching pipe, e.g. 508 x 11 mm to the raised face of the WN flange (DIN 2632 form C).

2. The problems arise partly because the contract specification we are working on, with flanged valves (DN 400 & larger) and counterflanges, was developed by a foreign consultant on behalf of the client. This specification does not reflect the client's actual practice of welding to the valves which seems to be an old Russian habit.

3. We have given practical reasons (heat-transfer into the valve during welding, welding of very dissimilar material, difficult weld preparation, stress-prone joint, difficulty to calculate the stress in the weld area etc.) to the client but unfortunately our site manager had stated that this practice was actually "prohibited". Now we are haunted by this statement.

We will anyhow decline the client's request because it's bad engineering practice and Tyco as the valve supplier won't buy into it. If the client does it on his own risk, well so be it.

Thanks a lot

Michael Focks
currently Visaginas, Lithuania

 

[tickle]

Are there any problems with heat distortion of the seals in the valves? I certainly would not be not be welding any valve unless it is designed as such

I have done a job with three piece weld end ball valves and the valves were supply without seals that were installed after welding

 

[JeroenPh]

Dear airfox2000,

If the target is to get a absolutely leak free connection joint you can use welding gaskets. These gaskets are provided with an extra steel lip which can be welded to the flange and to the lip of the other gasket after installation. This way you have a welded connection around the face of the flanges. See also the Kempchen web site:

http://www.kempchen.de/e/prospekte/pdf/007E.PDF

Regards,
Jeroenjacobs

 

[zdas04]

In nuclear plants, they use something called an "omega seal" (because a cross section looks like a Greek "omega" symbol) that is welded to each flange after make up. Might satisfy.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[makeup]

I reiterate, if you want to do this you will probably succeed, thats engineering, make it work. Whether its right or wrong will come out when/if your system fails probably in a court. All other points noted you are all right and another reason why I personally would not go this route.

 

[weldboy]

airfox2000,

In thirty years in the field and under a wide variety of circumstances I have seen what you are describing
done only once, and that during an emergency maintainence situation. To put it in the most polite terms possible,it seems slipshod.
However, in cases where valves sensitive to heat damage are installed in systems (such as when socket weld joints are used) the bonnets and caps are loosened and the interior working parts of the valves removed before welding, where possible.

 

[unclesyd]

I had (3) 4" Sch 80 SS lap joint flanges where I seal welded the edges of the flanges togather and use the backup flanges to carry the normal loads. 35 years later it's still in service and I don" think anyone except myself and the welder (deceased) ever knew. The service was 350 psi at 400°F.

Many years later I found this was a fairly common practice in some industries.

If this type joint has to be made a similar connection using a lap joint flange, may have to be cut down the gasket face to match the OD of the raised face or matched against the a flat face flange on the valve. Then use the backup flange and bolts to carry any load.

 

[juancaballero]

Why don't you try this?

1.-Remove the flange.
2.-Prepare beveled ends.
3.-Weld valve and pipe.

Maybe this can solve your problem.

Good luck