facing problem to choose between the monolithic joint (Joint Assemblies) and Insulating Flanges

[ismail06]

HELLO EVERYONE

I am facing problem to choose between the monolithic joint (Joint Assemblies) and Insulating Flanges
we have a metering station to be connected to a pipeline buried we would to choose one of them to be installed above ground before the buried pipeline
could some one give me the details taking in consideration the engineering point the comparaison between both and the advantage and the inconvenient if we choose one instead to other

Thank you in advance for your helping

Regards

Ishak

 

[LittleInch]

Monolithic joints cost a bit more but for pipelines are much better, especially for gas, as they avoid the use of flanges in an area outside of the valves. This is your key issue.

Isolating flange kits, especially RTJ flanges, are notorious for poor sealing and breaking of the rather fragile components, especially the bolt sleeves. You also sometimes need thinner higher strength bolts to accommodate the insulating sleeve. Order at least 1.5 times the number of insulating components. Even then Insualting flanges tend to fail over time and hence depress the CP protection in that area.

The only time when an insulating flange may be better is where you have highly conductive fluid. In these instances you need to internally coat only the pipeline side of the Insulating joint to reduce / mitigate against internal current flow and sometimes a flange is better as you can have removeable spools.

In most situations, the enhanced joint integrity of the IJ is much better and so is chosen.

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[BigInch]

Don't put the monolithic joint in a high stress location, especially high bending moment stress location. Also do not put it in a place inconvenient for maintenance, like somewhere that you have to shut down the pipeline to repair or replace it. Repairs to monos are difficult, so be prepared to replace it if anything goes wrong.

Technology is stealing American jobs. Stop visas for robots.

 

[LittleInch]

That's the problem though with all isolating systems, they are often the last / first thing above ground coming into a station so are nearly always out with isolating valves.

Not many IJs fail and certainly less than the flanges which often fail electrically, but then you can't repair them because it means de-pressurizing the pipeline.

True avoid the real high bending, but most nowadays most IJs can handle close to what a pipe can so long as the torsion is low - they hate torsion.

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

 

[ismail06]

bonjour

Thank you for all

just i want to share the real installation of the the exact location of the joint, it is located at the exit of our metering station before the buried pipeline on a distance
of 130 meters to tie in connection (see the schema below)
according to my installation if some can advice me to choose the right joint

Thank you in advance


Ishak

 

[BigInch]

The monos can also electrial short. If it happens, your cathodic protection system may not work for a very long time as there is no way to replace the monoblock without depressuring the pipeline. To be guard against that, I would move the valve upstream of the mono to the downstream side of the mono and call that valve the "end of pipeline valve". I'll bet the one that shorted out on me is still shorted out.

Since the pipe exits the ground, there is a chance of significant movement at that point = 1/2 x [α] x [Δ]T x Length_of_virtual_anchor. Not a good place for a perpendicular valve assembly as the pipeline movement may try to lever the assembly near the monoblock, especially if the fluid in the pipeline will be hot. What's the operating temperature? The thermal movement of the riser needs to be accommodated by adding an expansion loop, or another dog leg of some kind, between the monoblock and the pipeline riser coming up above ground, unless you know for sure that any movement will be very small.

If you move the valve, maintenance of the isolation device, whatever type you choose, will be much easier. I prefer flanges and isolation kits, as they are much cheaper and work just as well if placed properly. My opinion is that isolation blocks are a marketing trick. Why sell them something cheap if they are willing to buy expensive stuff. If either type shorts out between valves, they could be easily replaced.

Technology is stealing American jobs. Stop visas for robots.

 

[LittleInch]

BI, you seem to have had some trouble in the past and agree they can fail, like any other component if abused or installed badly, but so do flanges.

In general you want your IJ / IF to be the first thing after coming above ground. that way you avoid any issues with grounding the CP system due to contact with supports, pipe or valve earthing systems or hazard to personnel ( step touch shock).

However your piping layout is very poor from this design and will impose high bending loads on an IJ. An IF might be better, but those extra loads could crack the insulating components just as easily.

I wouldn't move the first valve myself - far more likely to end grounding your CP system through that than any benefit from being able to isolate. Design the system right first time around and reduce bending loads on the insulation to as low as possible.


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

 

[BigInch]

Yes, and ...... they cost more.

Technology is stealing American jobs. Stop visas for robots.