Where to place thrust block?

[LuisF83]

Hello friends:

According NFPA 24, each change direction in a pipe route needs an anchor block, for thrust pressure.

It is necessary for each change direction, aboveground and underground?

According construction department of the Company, they never see this anchor blocks, in any firefighting system.

It is possible to use a relief valve?

B. regards,

Luis

 

[msquared48]

I open air sprinkler systems used for buildings, the pipes are usually threaded together, so no thrust blocks would be required.

Not so for all underground systems where a lot of compression and unthreaded fittings are used. There is where you will need the thrust blocks.

Mike McCann
MMC Engineering

 

[LuisF83]

Hi msquared48

The system, I need to evaluate is a 16" diam, GRE pipe.

To join the pipe, we use a socket union, like socketweld, but with special resine, it is also necessary for aboveground systems, the thrust blocks?

Thanks for the help.

B. regards

Luis

 

[pennpiper]

Contact the pipe supplier, ask for a Technical Representative to come to your office and make sure you ask for all their technical bulletins.

prognosis: Lead or Lag

 

[B.L.Smith]

if you are using bell and spigot or coupling connections, you should use thrust/anchor block but for lamination types it doesn't need.

 

[LittleInch]

Luis,

Pennpiper and Bradsmith are essentially correct. Normally anchor blocks are only required for push fit type bell and spigot joints where if no anchor block was installed, the pipes would simply push the fitting off the end due to internal pressure.

GRE piping though has it's issues in terms of whether the joint you it sounds like you are planning to use (push fit with epoxy glue??) has sufficient strength. One of many issues is that the jointing process needs to be udertaken in clean envirionment and with experienced contractor otherwise there is a high risk of the joint not being made properly. Use of screwed and glued joints is more common for oil companies as this gives you greater reliability on the mechanical properties of the joint so if the gluing bit doesn't work it just leaks a bit, but won't fail completely. GRE also tends to have a tensile load when you pressurise it due to the Poisson ration of about 0.6 so can pull out of joints where anchor blocks don't work as they are normally designed for axial thrust, not compression. You need to have a good clean trench and surround as GRE can wear very easily on sharp stones.

It may not suit you now, but for buried applications, I would always start with PE as the base material for a fire main system unless pressure or temperature constraints prevented it as it is so much easier to install with GRE above ground or add concrete or cladding to short stubs of PE for fire proetection.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[bimr]

Thrust blocks have fallen out of favor because thrust block design is based on unknown characteristics of soils.

Thrust blocks were generally used on unrestrained connections (bell and spigot) for underground work. Most piping is now restrained in some manner using restraints such as megalugs.

Piping that is glued together is considered to be restrained and does not require thrust blocks.

 

[LuisF83]

Thanks for all answers.

bimr,

This is the reason, NFP 24 show forces only for PVC and ductile iron, since its connections are bell or spigot?

b. regards

Luis

 

[rconner]

GRE and/or fiberglass pipes are anisotropic, composite materials, meaning the strength of any particular pipe wall designed for a specific service is not essentially equal in all directions (e.g. in the sense of common steel or ductile iron pipe walls). The strength of the composite pipe wall in any particular direction is however dependent on the specific amount and orientations of the fiber reinforcements etc. that are actually contained within that pipe wall).
One cannot necessarily/therefore very precisely determine the strength of a piece of composite pipe in such regards as application to different structural (e.g. beam or thrust restraint) loadings or service just by looking at it, and say by measuring its wall thickness as with calipers etc. and applying a tensile strength or yield etc. value. Thus someone, with knowledge beyond rudimentary pipe hoop and beam design may well need be involved to confirm structural adequacy with regard to specific design and reinforcements, particularly for specific applications like non-thrust blocked or aboveground pipe on supports etc., that can involve far greater three-dimensional effects than unrestrained gasketed applications (normally one would hope installed with more or less uniform support in soil).

In the OP I also happened to notice "NFPA 24" was mentioned. While NFPA provides for both thrust blocked and non-thrust blocked, restrained joint systems, I did not however happen to see "GRE" or any other similar composite pipe material then listed/mentioned in same.