30" Transmission Main Connection

[Arambin]

Hello,

I am replacing part of a 30" DI water main with an average of 150 psi (max 200 psi). I am seeking different opinions as to how the connection should be made, and what type of thrust restraint to use. The new line I am putting in is all restrained joint, but the line I am connecting to is not. I have entertained the idea making the connection with a restrained coupling, but have been unable to find a manufacturer with the size needed. Also, I have thought about connecting it with a solid sleeve and using concrete to take the force, but the concrete volume is very large. Plus, if I pour that amount of concrete over the connection, maintenance problems will arise in the future. Has anyone else been in a similar situation? If so, what method of connection was used?

Thanks,
Austin

 

[ScottATL]

You may want to call Ebaa Iron, Inc. They manufacturer Megalug. They recently quoted me a tandem Megeflange flange adaptor that they rated at 300 psi for 36-inch DIP application. They may be able to do the same with the Megalug for MJ pipe. The tandem configuration is placing two restraining rings (the ones that dig into the plain end pipe) back to back.

 

[semo]

Depending on type joint type of the existing pipe, you will probably have to install retainers on numerous joints back from your tie-in to prevent the old pipe from pulling apart. Ebaa Iron has free software to calculate how far back you need to go.

Don't have much 30" stuff around here; but, on pipe up to 24" we have installed restrainer glands (what Scott is mentioning above) on new pipe then at the middle of the first old stick of pipe installed a retainer ring or two. This gave us something similar to a wall pipe around which we formed a concrete retaining wall. You must find out your soil bearing and size the wall (area, thickness, and rebar) to restrain the forces. This was done in lieu of the huge thrust blocks you describe.

 

[BRIS]

If the original line did not have restrained joints then it must have thrust blocks at each bend. If you are replacing the pipe then the thrust blocks must already be in place !!.

Presumably you are now using restrained joints either because you have changed the alignment or the existing thrust blocks are deficient for some reason.

As suggested above you have two options:

1) Provide an anchor block at the connection.
or
2) Replace more of the original pipeline with new pipeline with restrained joints for a sufficient length to dissipate the tensile thrust.

In either case your joint between old and new will e a simple spigot and socket (bell and socket) joint. If the outside diameters are slightly different you will need a stepped coupling.

BUT you need to determine why you have a thrust at the connection.

You will only have a large thrust if there is a valve, bend or taper immediately downstream of the connection. In which case you would be better providing a concrete anchor at the fitting that is causing the thrust. If you do not have a fitting immediately downstream of the connection then some (or all)of the thrust will have been transferred into the surrounding ground.

In summary you are trying to solve a problem that should not have occurred in the first place. You need to reconsider your design.

Brian

 

[KRSServices]

Is your tie-in a tee? Or are you replacing a section of pipe?

The connection is relatively simple and straight forward unless you are installing the new pipe as a tee connection or coming in with bends to adjust for your alignment.

Either way, this is not rocket science, but as a footnote, I would not get too excited about reliance on megalugs or other pipe restraining devices. As I have stated many times, the pipe is not necessarily designed to act as a restraining device and therefore may prematurely fail if the surge pressures overcome the pipe's ability to restrain. This is of particular concern at tees and bends.

KRS Services

http://www.krs-services.com

 

[Arambin]

Thanks everyone. I am replacing existing pipe after a 22.5 degree bend. I finally determined that I needed to rip out and replace 40 LF of the exsiting pipe with restrained joint, then make the connection with a solid sleeve. Attached to the sleeve there will be a welded on thrust collar, with a concrete collar for restraint. This will dissipate all the thrust from the pipe into the soil.