Flexible Coupling

[GeorgeMech]

Hi! I have a situation where the consultant requires the system to be provided with flexible joint whenever the pipes are passing through building expansion joint, however, our building does not belong to a category that requires seismic protection, however, the consultant insist that we need protection to compensate the thermal expansion of the pipes, so the question are, is it really requires that the fire fighting pipes shall be provided by victaulic (flexible) coupling and is it only at the location where pipes are passing through building expansion joint.

 

[ForestWilson]

I don't have NFPA 13 in front of me now, But the chapter you are referring to is specific for seismic protection.
In the USA, the Building Code determines if the area is in a seismic zone and the Layout Technician of the sprinkler system uses NFPA 13 Chpater on Seismic Protection.

In your case, it sounds like the Engineer of Record (EOR) is insisting on specifying flexible couplings irrespective of the Building Code.

If your specs require you to "install per NFPA 13" then I suggest you send an RFI such as: "Spec requires layout and installation per NFPA 13. However, Spec requires flexible couplings when not required by NFPA 13. Please provide guidance and clarification on this"

 

[Duwe6]

The "stand answer" to pipe thermal expansion is an Expansion Loop, and your engineer wants to 'reinvent the wheel'. I would decline to install a flex-coupling in a firewater system without a signed drawing detailing the pipe & coupling installation. Because it won't work.

Pipe expansion is linear - it gets longer & shorter. A Flex-Coupling allows lateral, bending movements - thus they are necessary to survive a major earthquake. A Flex-Coupling does not allow for linear movement; they tend to leak. The standard non-expansion loop "pipe guy" answer for linear expansion is a bellows expansion joint. They work well but have two major limitations, one that applies to your instance.

1) Metallic Bellows pipe/pressure vessel expansion joints have a fatigue life of about 10K cycles - probably not a firewater system problem.
2) They are delicate - the bellows material is only about 0.045" thick. Dropping a 10" crescent wrench 15-ft onto one will ruin it and may even puncture it. Stepping on one will crush it. If I was forced to use a bellows in a firewater system, I would protect it by putting it inside a large pipe sleeve - freefloating, not in contact with the firewater line or the bellows. Just a 'tunnel' to protect the bellows.

 

[GeorgeMech]

Thanks for the reply. First, our building is not under the seismic application with reference to the IBC code so that is why we did not used any sway brace in our piping and so I insisted to the Engineer that this flexible coupling attached to the piping (whenever pipe is passing through building expansion) is not required, same explanation you mentioned above, however, the next question of the engineer is, how about the thermal expansion of the piping, what will be the protection for this matter. Here in the middle east, the maximum probable temperature range inside the standard building (assuming the Air-conditioning system is off especially during night time) is around 20degC during cold season and up to 40degC during summer and applying the thermal expansion formula, the result is very minimal (2.34x10^-4 m/m), but the bottom line is, is the resulted value for the expansion can still maintain the integrity of the piping?