Seismic Applications

Shortly after Metraflex introduced the first flexible pipe loop (the Metraloop), it became the standard used by engineers and designers to protect piping systems in seismic events, exactly what you would expect from something invented by a person named Jim Richter.  Metraflex has been leading the way with seismic solutions ever since.

All the Metraloop, V loop, and Dog leg products are all ideally suited to be used for seismic applications.  The low spring rates, movement in all directions, and that they do not impart any thrust loads on the piping reduce loads on the seismic bracing make them ideal for seismic applications.  Additionally, these products are capable of movement in all six planes.  

All these products are available in standard configurations and customized versions, tailored to meet your projects requirements.  Additionally, the Seismic Gator was developed to be used when there was not enough space to use a Metraloop. 

Application and Installation

We have found that the construction requirements to install a functional seismic protection system for piping systems is ahead of the building codes themselves.  Outside of any local codes, the only national code that we are aware of that gives us guidance of how to install a seismic device is NFPA 13.  Although this is only mandatory for fire sprinkler water, it is a good basis of design for other systems if local codes do not exist.

NFPA 13 specifies that that the seismic device / flexible pipe loop be no more than 2 feet from the seismic separation.  It also specifies that the bracing can be no farther than 6 feet from the seismic separation.

One of the most common seismic questions is; how do you fit in a Metraloop where the seismic separation is located between two walls that are close together?

You would need to create a seismic clearance in one wall as shown below.  The seismic clearance needs to be the seismic movement plus 2 inches per NFPA 13.  If you do not have this clearance a seismic event would shear off the pipe.

You would then place the Metraloop on the same side with the seismic clearance and put the brace on the other side of the Metraloop.  If the customer is concerned with an open hole, this can be sealed with a sheet metal escutcheon plate that would yield during a seismic event and need to be replaced afterward.  There are also companies that offer a rubber boot for these applications. Be sure to inspect all loops after a seismic event.

Another common question is if thermal and seismic movements can be combined into one devise.  This is an important consideration since we have seen cases where the seismic movement had been addressed without any consideration of the thermal growth of the piping.  One device can be used for both seismic and thermal movements can be done if:

1. The seismic device (Metraloop, V-Loop, or Dog Leg) is sized for the combined movement of the Thermal and Seismic loads.
2. The seismic braces next to the seismic device are replaced with guides.  Typical Spider Guides with a corresponding pipe hanger is shown in the detail below.

Note:  Make sure the guide is also sized for the combined movement.

In Line Seismic Joints

For installations where there is no room to install a Metraloop or V Loop, Metraflex has developed the Seismic Gator that is designed to handle movement in all directions.

The in-line profile is achieved by utilizing a combination of an externally pressurized joint, the Metragator, and a pair of gimbal joints on each end. The Seismic Gator is a rugged and reliable joint, but it will develop high thrust loads like an in-line bellows, unlike the Metraloop which develops very low loads.

Seismic Breakaway Hanger

Another Metraflex innovation that facilitates the successful installation of seismic joints in the toughest installations is the seismic Breakaway Hanger. The Seismic Breakaway Hanger is used as a support for a seismic device that will release in a seismic event allowing the seismic device to move freely.

See below details on how the Seismic Breakaway Hanger is installed:

To ensure your seismic devices (Metraloop, V Loop or Dog Leg) will perform properly in a seismic event, it is very important to use a Seismic Breakaway Hanger in the following situations.

1. Whenever the seismic device to installed to close to the deck of the structure.  The seismic device needs to be installed at a distance of a minimum of two times the seismic movement minimum 12” or during a seismic event the seismic device will swing into the structure causing damage to both the structure and the seismic device.  The picture below shows an example of a +-30 Dog Leg with a seismic Breakaway Hanger installed.

2. For applications with large movements that require longer hose lengths.  The hose section will likely sag, so an intermediate support is required to prevent this sag.  This is very important for plumbing system applications that require a proper pitch.  The solution is a Seismic breakaway Hanger installed with a saddle on the hose as shown in the detail below.

3. To ensure that both sections of hose in a seismic device move freely and evenly.  What a lot of designers and users do not understand is that in a seismic event very often one leg of a seismic loop takes all of the movement, while the other leg sees very little movement as shown in the details below.   The simple solution is to install a seismic breakaway hanger in the support rod, so that in a seismic event it will release allowing both sections to move freely and evenly.

After any seismic event, the Seismic Breakaway Hanger can be simply reset.

How Not to Install a Seismic Device.

In the below picture you will see a set of seismic Metraloops installed over a seismic separation.

If you look closely, you will notice that the top of the loops is supported with a rigid hanger.  If the structure on either side of the seismic separation moves in the Z axis (vertically) the sections of hose will either be pulled apart of over compressed.  It is always important for a successful installation, for both seismic and thermal applications that the top of the loop be free to move freely.

In this case the solution is simply installing a Seismic Breakaway Hanger at the top of the loop.  In a seismic event it will release, allowing the loops to move freely without damage.

Base Isolation Systems

Base Isolation seismic systems is an alternative to the traditional design with seismic separations.  In a base isolation system, the entire structure is supported by base isolators that will allow large amounts of horizontal movement.  Horizontal movements of 36” are common, vertical movements are usually 1 or 2 inches.  This is an ideal way to retrofit seismic protection into an existing building.

Metraflex considers seismic joints for base isolation systems to be engineered products. Contact Metraflex or your local representative for more information.

The engineering staff at Metraflex has decades of combined experience. 
Please feel free to call us to review your application.

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