Flange connections vs. pip couplings 3

[MartinLe]

For a while now, I'm wondering about the relative pros and cons of pipe couplings (like this:

https://www.straub.ch/fileadmin/Str...ntageanleitung_straub-grip-l__metal-grip.pdf)

vs. flanged connections in piping.

[ul]
[li]From actual quotes from contractors, I see no huge difference in price between a flange connection (consisting of collars and loose flange or two fixed flanges and bolts/work) and a coupling.[/li]
[li][/li]
[li]Couplings allow some play in distance between the pipes (up 45mm in large pipes if I read the sheet correctly and use the extra band)[/li]
[li][/li]
[li]Installation time should be far quicker if I consider the time for welding[/li]
[/ul]

... so it looks like, for pipe-pipe connections, these couplings have a few clear advantages (That may not always be relevant!). What are downsides, relative to flanged connections?

The applications I'm dealing with are wastewater, water, maybe sludge at up to piping PN16 and temperatures in the 0°C - 100°C range; and sewage gas in a pressure range up to 100mbar and the same temp. range.

 

[LittleInch]

For pipe to pipe joints you really should be comparing it to welding. One weld, no materials easy.

Flanges - two welds, two flanges, bolts, gasket.

Key issues
Your seal is wholly dependent on the "rubber" seal
I notice it says "In case of leakage..." tends to mean it happens a lot
The axial force capability is terrible and hence you need anchors and thrust blocks at all changes of direction
They might claim to be axial restraint pipe but I couldn't see a max axial force anywhere and whatever it is it will be a lot less than a weld or a flange
expansion capability will be limited
Bending force capability is also terrible
Don't know where you get 45mm from. With strip insert it says 35, but is this really needed?

The pipes it is attached to will need to be clean, very round and cut straight. Installation time will be lower, but is it that important?

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

 

[mk3223]

IMO, it may based on the operation experience and the consquence of the fluid leakage from the pipe joints. Also, the material selection may be limited by the service temperature.

 

[MartinLe]

Background to the question is twofold:
I've seen these in wastewater (never gas!) installations designed by other firms and so I wonder if this is an idea worth copying.
I'm right now in an early planning stage for refurbishments for a sewage gas installation. Keeping the time the installation is out of commission short is a bonus.

LittleInch,
It can be neccessary to have flanged connections, there's places you could weld a collar or flange but you can't weld a large pipe.
Your other points are noted.

 

[MickMc]

Normally in my experience in O&G flanges are minimised, both in process and utility service, as they are potential leak paths and flanges usually found adjacent to equipment where you would expect to see majority of valves, inline instruments and nozzles with the exception being internally coated piping which will come in flanged spools unless diameter big enough to field apply coating at welds. As for being neccessary to have flanged connections because you cannot weld the pipe I would not expect this to be the case as having flange connection would increase the minimum spacing between pipes and/or structure with the specified minimum spacing already taking into account field welding but the OP may have experienced different in the field.