Schedule 80 for underground fire protection supply - outside of the building 5

[DDE305]

I am looking at a job where the supply line is a 6" schedule 40. The owner will be changing to to a schedule 80 and we plan to connect to that to supply the fire sprinkler system. My question is, is schedule 80 allowed for underground piping to supply the fire sprinkler. Or is C900 the only piping allowed? Is there any specific code for this? It seems that the schedule 80 (grey) has a higher PSI rating than the C900 - any help would be greatly appreciated

 

[bimr]

Local building code regulations differ regionally, so consult the local building code office for requirements when any PVC pipe is installed.

PVC piping with glued joints is not generally recommended because the joints are rigid and will break when the ground moves.

A PVC piping installation will also require the use of thrust blocks to try to control the pipe movement.

The recommended pipe joint for underground piping applications is a flexible joint. The flexible joints will allow movements of the piping system. With a rigid pipe system like PVC, the joints will break as the piping moves causing leaks.

The Owner has probably experienced problems already which is the reason that he is interested in a stronger pipe.

This has been discussed before in the link:

Previous Discussion

 

[DDE305]

Thanks - for the info and thanks for the previous link. With that said, yes the thrust blocks are the important thing and the c900 is a choice.

 

[bimr]

There are few people that still use thrust blocks, most knowledgeable engineers specify restrained joints. Thrust blocks are not generally recommended anymore for a number of reasons:

Thrust block discussion

 

[1503-44]

They usually put the thrust blocks where they will in fact be guaranteed to break the pipe.

A black swan to a turkey is a white swan to the butcher.

 

[XW1968]

I've never heard of schedule pipe being used as a service line or fire-line. I think you’ll want to go with C900-DR14, which is a bit thicker than Schedule 80. C900’s O.D. will work with standard AWWA ductile iron O.D. valves and fittings. You can provide restraint by using retained joint pipe and retainer glands, or push joint pipe with thrust blocks at the bends and thrust collars at the valves.

Sorry, but I have to disagree with some of the comments above. Thrust blocks are still commonly (and appropriately) specified.

Push joint pipe is cheaper and easier to install than restrained joint pipe, and backing block failure is not a problem. Almost all main installed for new development in our area is push joint with thrust blocks.

Retained joint pipe itself is more expensive, but it does have its advantages and is the right and less expensive choice in certain situations, like:
[ul]
[li] you expect signification conflicts with other utilities that would otherwise require lots of bends and blocks relative to the length of pipe, and/or the blocks would be at difficult or inconvenient spots to install.[/li]
[li] there is a something behind the bend and you can't rely on the soil for support, like a retaining wall or a large storm sewer.[/li]
[li] soil conditions are poor and wouldn't support a backing block,[/li]
[li] when directional drilling and pulling pipe,[/li]
[li] you don't have time to wait for thrust blocks to cure to get a main back into service,[/li]
[li] installing through a long casing (so you need to pull the pipe),[/li]
[li] for larger diameter mains (like 24" and bigger) where the size of thrust blocks become impractical[/li]
[/ul]
Actually, on most projects it’s a mixture, with sections of both push joint and restrained joint pipe specified where it makes sense.

 

[bimr]

Push-on joints on straight pipe runs don't require restrained joints. Restrained joint systems function in a manner similar to thrust blocks, insofar as the reaction of the entire restrained unit of piping with soil balances the thrust force. These joints offer flexibility and are simply and quickly installed. Restrained joints are a better alternative than the use of thrust blocks, and do not replace push-on joints on straight piping runs.

"The use of thrust blocks should be considered with great care. They are only as good as the stability of the soils used for reaction backing. In locations where the soils may be disturbed by future excavations (yard piping, treatment plant sites, busy streets, etc.), reliance on thrust blocks (particularly for large diameters and high-pressure pipeline systems) is not a very good idea. Instead, the use of restrained (lugged or harnessed) joints and trench friction is a better approach."

Pumping Station Design, Third Edition, 2006

by GARR M. JONES, PE

It has been argued that thrust blocks are the cheapest form of pipeline restraint. When all of the costs such as labor, forming time and waiting for concrete to be poured and cure is added to the price of the concrete, the thrust block is not as cheap as originally thought. Any time you a geotechnical engineer for a horizontal bearing pressure to use in the thrust block design, the geotechnical engineer will put in so many factors of safety on it you end up designing your block for a soil with the consistency of custard.

A properly designed thrust block involves much more than “dumping” a load of concrete (or throwing a bag of portland cement) behind a bend. The design involves consideration of undisturbed soil, soil bearing strength, test pressure, pipe size, fitting configuration, and trench depth to determine the bearing area of the thrust block. It is then a matter for the installer to form up and pour the proper block. Care needs to be taken to prevent the concrete from covering the joints at fittings, the weep holes in hydrants, and operating mechanisms of valves. Once the thrust block has been properly designed and properly formed, a concrete truck must be called to the site to pour the concrete. Now the waiting begins. Only after the concrete has cured can the pipeline be charged with water and tested. This procedure addresses horizontal fittings. When complicated bend combinations, vertical downbends, parallel lines, dead ends, and future excavation possibilities become involved, the use of thrust blocks become very problematic. This report does not begin to explore the combinations involved with thrust blocks in locations with poor soil conditions.

Can you really eliminate thrust blocks using joint restraint? Based on years of experience, the answer is “yes”. The use of the EBAA Iron mechanical joint restraint products and proven design procedures allows for reliable installations that effectively eliminate the need for thrust blocks. The use of the mechanical joint enables field adaptability that is not available with all joint restraint products. Pipe can be cut in the field and fittings assembled with simple procedures that allow for the prompt acquisition of materials and completion of construction. All of this combines to provide you with a safe and proven piping system without depleting your resources.

Link

 

[jgailla]

I work in the southeast US and I can't recall thrust blocks being allowed by any utility.

 

[Pipe_Dude]

Reference NFPA 24 and your local FD for underground fire material requirements. Some local FDs change requirements every year.

 

[KaBone]

Check the local FD code; that should tell you which NFPA version to use. Sch 80 doesn't sound right to me in this application.
Regarding the thrust block sidebar - Navy told me they don't allow restrained joints because the thrust will still push on the bend and the bell and spigot will open up. I think a combination of restraints and thrust beam is best.