Live steam piping valves joints type

[Pederator]

Hello all,

I work for the company that is currently technical advisor for the construction of CHP plant. The contractor wants to use flanged valves on the live steam piping DN200 PN100, 40 bar, 400 deg C. From my information, welded joints shall prevail. Can you tell me what is your opinion about this? Maybe there is some standard which defines in which applications either types of joints are to be used (European standard preferred).

Thanks in advance for help.
Pederator

 

[gerhardl]

No EN (European norm) comes to mind that require welded valves only. I have however not actually cross-checked this.

At the given temperature and pressure it is of course imperative that both valves and flangeform and flange sealings and material are suited for the application.

Ringtype joint form on flanges and or carbon glassfibre reinforces materials comes to mind, without checking if this is recommendable for the application.

Also note that Europe has a larger number of manufacturors specializing in steam valves and other pipeline components for steam. Search homepages for further info. (Inlet and release valves, steamtraøps etc.)

 

[GHartmann]

I don't believe that would be the case. It all depends on the "corporate" pipe code. For the system I have utilized valves 2" (50mm) and under shall be welded (I still prefer flanged for 2"). 3" (76 mm) and above shall be flanged.

For the ASME systems flanged valves are utilized in the larger sizes up to a pressure rating of 2500 # (173 bar). Once 2500# is reached many valves now only come with "buttweld" connections.

Sorry for referring to the ASME system, but perhaps the conventions I have seen may help you better understand the EC system.

 

[MJCronin]

I agree with Ghartman.... It all depends on the piping code specified by the engineer of record.

There are legitimate reasons to choose weld-end valves, most of which are for high-pressure steam or for toxic/lethal service where leakage at a flange face is not permitted.

This is a superb reference...

http://www.valvemagazine.com/index....kets-required-weld-end-connections-for-valves

I would expect to see weld-end valves in large diameter,(>6 inch NPS) HP steam systems.... in what would be Class 900 and higher.

What I don't understand is the reason for the contractor's request........

When the cost of the HP flanged valve as well as the adjoining piping flanges are included (they will probably be weld-neck), I believe that his total cost will be more expensive.!!! Furthermore, the new flanged valve (with piping flanges) may not physically fit in all locations. ! ! Is this contractor so savvy as to be indirectly) generating future cost extras with this change !

What is his reason for this change ?

MJCronin
Sr. Process Engineer

 

[Pederator]

Thanks for your valuable comments. The design code is EN 13480-3. I do not know the reason why contractor wants to use flanged connections on valves. Maybe unification of supplies, as all - or at least most of - other valves (eg. on turbine bleed pipings) are flanged, or just experience / habit / custom / practice of the company in designing pipings with flanged valves. Another reason may be the time savings and ease of exchange a valve - technical, as well as procedural - in case of some problems, as contractor already has serious delays in execution of the contract, and every week is significant. Obviously, if the plant will not be ready to operation (after commissioning) until contract "deadline", contractor will pay penalties.

Once more thanks for your involvement on this issue.
Pederator