Valves with butt welding ends 3

[Prototyp]

Dear community,

Usually we use carbon steel piping in our factory with screwed end connections for small pipes (smaller 3 inch/ DN80) and flanges for larger sized pipes (larger 3 inch/ DN80).

Since butt welded connections are best regarding leakproofness we are considering to use valves with butt weliding ends instead of screwed or flanged ends.

I don’t have any experience with butt welded ending valves and couldn’t find proper information which I need to write the specification. Therefore following questions:

Which material does the valve body need to have to enable easy and high qualtiy welding with carbon steel pipes?
Are welded connetions cheaper than screwed or flanged connections?
Anything else that needs to be considered?

 

[LittleInch]

Valve body material just needs to be a similar material to your pipes.

what is often done is that you supply the pipe to the valve vendor and get him to do the pipe/valve welding which also helps because they can do it with just the valve body before inserting any internals. You can get valve or seat damage due to welding, more for smaller valves than bigger diameters.

This way the annoying weld procedures for pipe to valve are the vendors concern and you get a nice easy pipe to pipe welding the same as any other. If not then you need some valve material blocks to do weld procedure testing on.

Cheaper? Hmmmm - the valve is often a bit cheaper as is the transport due to less weight, but difficult to calculate total costs without knowing the cost in your location for welding vs bolted or screwed connection.

So yes, better for leaks etc, but more hassle if you ever need to remove the valve for maintence / leaking etc so make sure you get a top entry valve where you can remove / get access to the valve internals without having to cut the valve out.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[curtis2004]

Prototyp,

What is fluid flowing inside piping? Do you know operating temperature or pressure?

Yes, sometimes process conditions dictate using welded valves instead of threaded or even for flanged.

Why would you want to use butt welded instead of socket weld?

Thanks,
Curtis

 

[Prototyp]

"What is fluid flowing inside piping? Do you know operating temperature or pressure? Yes, sometimes process conditions dictate using welded valves instead of threaded or even for flanged. Why would you want to use butt welded instead of socket weld?"

Fluid and temperatur is not a problem (emulison or oil, 10 to 40 °C). My thought was that flanges could leak and the gasket might be replaced after somme time. Moreover flanges have to be welded to the pipe ends, gaskets need to be purchased and the connection needs to be maintained. So my idea is that welded connections might be more effective regarding costs and quality.
I guess butt welded connections prevent better from corrosion as there won't remain a gap between the pipe ends.

"Valve body material just needs to be a similar material to your pipes"

Valve bodies are usually made of cast iron, ductile iron or stainless steel. So these bodies would not fit to carbon steel pipes?

 

[LittleInch]

Not many valves I deal with are made from cast iron or ductile Iron, which tends to be a water industry standard material, but then they usually use Ductile Iron or PE for pipe.

You can weld stainless to Carbon steel, but you have to question why you're spending money on a stainless valve then connecting it to a carbon steel pipe??

Yes flanges can leak, but if they are built properly they don't. Hence welding for this reason is not normally a big consideration unless the contents are highly hazardous or toxic.

One thing to consider is that it is common for pipe spools to be made off site and tested, painted etc then transported and bolted up at the actual site. Welding in valves complicates this a LOT as it increases weight and can increase spool length making them unwieldy.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[moltenmetal]

Typical pipe selection works as follows:

For linesizes 1/2"-2", for services of low leakage hazard, threaded piping fittings and valves are used.

For linesizes 1/2"-2", for services of modest to high leakage hazard and modest to no cleanliness/crevice corrosion hazard, socket-welding fittings and valves are used.

For linesizes 3"+, and for 1/2"-2" linesizes when crevice corrosion or cleanliness are somewhat a problem, butt-welding fittings are used. Valves are either flanged or welded depending on how much valve maintenance is expected, the size and criticality of the service etc.

You don't generally jump right from threaded to butt welded, and generally you don't butt weld valves of small linesize unless there's a fairly good reason to do so.

 

[Prototyp]

Welding cast/ductile iron to carbon steel is possible but difficult. Welding stainless steel to carbon steel is possible but might lead to increased corrosion at the carbon steel pipes I guess?

So it looks like valve bodies with welding ends are not the best solution for carbon steel pipes.

 

[KoachCSR]

Welding ends for valves for carbon steel pipes are very common in many industrial applications - as pointed out earlier in this thread, it's beneficial when the fluid is hazardous or toxic, as well as for saving weight in the line, which can translate into reduced costs for supports over the course of the system during installation (must be weighed against maintenance needs, of course).

It is not my experience that most valve bodies are made of cast or ductile iron in industrial applications; typically, carbon steel valves in our specs utilize A-216 or A-105 - cast or forged, depending on valve size.

 

[moltenmetal]

In threaded lines 1/2-2", in services of low corrosion hazard, cheap CF8M cast stainless steel valves are often used whether the line material is carbon or stainless steel. In the old days you might have used cast brass threaded valves instead. That is sometimes still done, but it saves very little relative to stainless these days.

If you switch to socket welded for 1/2-2", you'll be using forged steel gates, globes and checks and not bothering much with ball valves unless there's a particularly good reason to use them if you go with carbon steel. In stainless steel, you can use socket welding versions of the 150# threaded CF8M fittings and valves (including 3 pc ball valves so you can disassemble them prior to welding) as long as your corrosion service doesn't cause you problems with the fact that CF8M is not a low carbon cast spec- you will get weld sensitization if you weld this grade to itself or to 304/L or 316/L pipe. The same fittings in low carbon CF3M are much less common, but when this grade is used, the corrosion resistance post welding will improve. The step up to forged fittings (3000# socket weld) and forged stainless gates, globes etc. is a big step up in cost.

 

[curtis2004]

Prototyp,

I would use class 800 forged steel valves with bolted bonnet and with socket weld ends, and 3000# socket weld fittings for your application. All welded construction.

Thanks,
Curtis