CSA Z662 Canadian Pipelines code - buried flanges - your thoughts 3

[bdp6632]

Hi, quick question - CSA Z662 is pretty quiet on buried flanges in their design which could be translated as it is allowed to use. I know that certain client codes and specifications "discourage" the use of underground flanges, but sometimes these cannot be avoided. I am not talking about flanges associated with valves, rather, flanges used for code transfer between CSA Z662 (pipeline code) and ASME B31.3 (piping code). Sometimes this could happen inside plant boundary or close. Client specs can be justified by getting a deviation presenting your case. Would like to have someone share their thoughts or if there is a particular clause in CSA addressing this issue, please share. Thanks in advance

 

[1503-44]

Things not prohibited by the codes are not prohibited.
Underground flanges have many uses, especially for allowing convenient future connections or modifications, connections between different pipe materials, electrical isolation, instrument connections, fabrication and fit up (misalignment flanges) and certain maintenance activities.

Which code, as you say, "discourages underground flanges"?

 

[HTURKAK]

When you write ( buried flange ) and search the forum, there are 263 records ..and probably some of them will be answer to your specific case..

I am thinking now,some threads has a certain period ..like merry go round ..



thread378-263975

thread481-241408

thread292-82015

thread378-350800

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[saplanti]

None of pipeline engineer would like to use flanges buried even if it is for code boundaries. The good practice is to raise pipeline locally and make the connection aboveground. In case the pipeline continues with piping in line in the plan view you can use a goose neck to make this connection. In case the connection is in the middle somewhere on the pipeline you raise the pipeline locally with or without expansion joint and attach the pipe branch on to the pipeline either with flange or welding.

I did not explain the reason why pipeliners do not like the flanges buried. The main reason is corrosion, second maintenance. You cannot see if there is a leak or not at the flange connection. There is another reason from the pipe stresser point of view, it behaves like an anchor in the compacted soil. It creates more problem.

There are flanges underground, but in a ditch and reachable, maintainable, can be seen from outside, or in an isolated room.

I trust this is sufficient for your question.

 

[LittleInch]

In the same way there is no real reason to HAVE a flange as such a location. A simple welded connection could / should be used which may need a special transition piece to bridge the difference in wall thickness between the two different strength materials, but so be it.

Like said above, most codes tell you how to do things and not provide a list of things which you can't do as the list would be very long...

So it's silence on this also speaks volumes - i.e. it doesn't cover it.

Buried flanges are not a great idea - impossible to monitor for leaks, subject to all sorts of corrosion - bolts, inside surfaces and act as a stress concentrator. If you're going to do it cover the whole inside surfaces with grease and add a flange protector (basically a steel strip which goes around the outer edge of the flange).

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

 

[alchemon]

Most of my clients don't like them but will use them if push comes to shove.

Here in the southeastern US, insulated flanges are used as custody transfer points (between transmission and LDC; or between LDC and industrial plants). Often they are buried. Rarely do they leak if properly installed.

I think the worst utilization for a flange underground is at a valve, since if the flange leaks, it can be very difficult to repair (as you may not be able to utilize the valve to shut off flow).

If an underground flange can easily be isolated/shut in for repair, I wouldn't ever "prefer" to use one, however, I wouldn't be overly concerned if one had to go in for a specific reason.

If it were me, I would try to design as many custody transfer points utilizing a flange to be aboveground. But that is a personal preference, and there are countless buried flanges out there which are not leaking.