Why use welded steel valves in district heating system? 1

[janie09]

Dear All,

I want to know why use the welded steel ball valve and butterfly valves in the district heating system? What's the advantage?

Thanks very much!

Janie

 

[Danlap]

Hi Janie,

I don't have experience in regards with district heating system in terms of maintenance strategy and expected lifetime (with or without maintenance).
District heating system means two basic things:
- winterizing temperature and then summer. In addition with intermittent usage (not in full capacity the whole year?) --> at some extend may help (thermal) relaxation on bolting flanges, thus creates leakage path
- the pipeline passing through communal area either beneath or above the ground. It is not desirable shall there is leakage under someones houses or even periodic maintenance performed involving crane and other heavy machinery. Hence, the district heating system maintenance strategy is predicted end of lifetime e.g. 30 years or 50 years of total replacement.

The idea of using welded ends valve is usually to minimize leakage path of the medium.
Sketch courtesy of danfoss

Imagine if the network have several heating leakage point, then it will be an energy loss.
However in every x kilometer, normally the pipeline goes into metering skid or pump station where actual maintenance is schedule every y year. IMHO for maintenance purpose it is advisable for valves in this location disassemble-able (read: with flange)

other thing, since this the pipeline located in the communal area, there is also a slight chance that valves are prone for vandalism (stolen or bolts deliberate loosening). I've seen this in some unmanned platform.
Why ball and butterfly? common practice and process related.

Regards,
MR

https://nosuchvalve.com

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376

 

[LittleInch]

In general buried flanges are to be avoided as they are a weak point in your system from a corrosion / leak path view point. However it makes valve replacement a bit harder, but sometimes buried flanged flanges are very difficult to remove and you end up torching all the bolts off any way as they've busily corroded on you....

Also you still need one weld to weld on the flange either side, plus bolts plus gasket plus fitting time and flanged valves are sometimes more expensive than their WE colleagues so can be cheaper on the CAPEX side.

So buy decent valves and weld them...

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

 

[janie09]

@Danlap

Hi, Like you said, What's the difference between fully welded pipeline ball valve and district heating ball valve?

 

[Danlap]

Hi Janie,

http://heating.danfoss.com/pcmfiles/1/master/other_files/library/heating_book/chapter5.pdf

My assessment is only based from seeing your quoted picture and above literature briefly. I don't see the significance difference in ball valve type for many general industries.
However the international or local standards used; government regulation and material applied might be different between one application to another. And indeed the more quality standards required for valves will increase the valve price.
For example, if you're talking about heating power plant with coal based fuel and located in Europe. Europe have a very strict emission standards, hence valve must according to certain Fugitive Emission Class.
Standard valve with no fugitive emission requirement will be lesser price compare to the one with.
As for the distribution line with hot water or hot gas as medium, om which both are environmentally save (shall leaking), therefore in this line probably the requirement is less strict.

Again I am not district heating expert and I fully endorse LittleInch approach, descent valve and weld it (if indeed butt-welded end for some reason is the general requirement).

Regards,
MR

https://nosuchvalve.com

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376