Concrete encasement of ductile iron pipe fire main 1

[RMonteiro]

Is there any recomendation against the concrete encasement of a fire main with working pressure of 10bar in ductile iron pipe? Shall I execute some special protection on the push-on joints and mechanical joints?
Thanks!

 

[Maury]

What is the reason for the concrete encasement?

 

[SlideRuleEra]

On industrial sites we used mechanical joints for fire protection lines to provide a higher level of reliability than push-on joints. DI pipe may be encased in concrete, under the right conditions.

Be sure to consider proper thrust restraint, see "Thrust Restraint Design for Ductile Iron Pipe" from the Ductile Iron Pipe Research Association (DIPRA). Here is a link

http://www.dipra.org/pdf/thrustRestraint.pdf

For exterior corrosion protection of buried pipe, consider polyethylene encasement. See "Design of Ductile Iron Pipe"

http://www.dipra.org/pdf/designOfDIP.pdf

and
"Polyethylene Encasement Installation Guide"

http://www.dipra.org/pdf/PolyethyleneEncasementGuide.pdf

http://www.SlideRuleEra.net

 

[RMonteiro]

Thanks for the comments. The encasement would prevent pipe movement and enable faster sealing of the original soil. I am working under tropical rain every two days, which delays substantially the backfilling.

 

[DRC1]

I would be sure that you have good bearing perhaps stone bed, as the encased concrete would be prone to settlement, nad the DI would not tolerate a lot of settlement.

 

[rconner]

While not sure of the necessity for same in your application, I believe ductile iron piping has been encased in concrete with good success for many decades and purposes (many decades before that, I suspect some gray cast iron piping was similarly encased). About all else I would say is that if the main is to be concrete encased, it may not be a bad idea for some sort of/e.g. at least a low pressure test be put on the installed piping before it is finally encased. The reason for this is that once cured the concrete encasement would likely prove much more difficult than normal buried soil embedment to dig and remove from around the piping, e.g. to find and readily fix any sort of leak from whatever cause detected in the process of finished project acceptance testing etc. If a pressure pre-test is performed for example of exposed piping laid on top of a trench bottom "slab prior to finish encasement, I have also seen some folks pre-embed in effect sort of stirrup anchors periodically in the slab under/along both sides of the pipe, so that the piping can thereafter be in effect "strapped down" to the slab (such strap-down anchorage is generally most effective if purposefully pre-located to be immediately behind bells). The purpose of properly designed anchorage may further be two-fold, one for providing lateral thrust resistance to prevent movement of flexible joints for essentially exposed pressure testing on top of the slab, and two for holding even large empty mains in place vs. movement/buoyancy forces per Archimedes as a result the subsquent placement of heavy liquid concrete around same. If a purpose of the concrete encasement is not for "waterstop" (to prevent water from running along the pipe through the encasement etc. like through some water/ tank walls etc.), some folks also wrap polyethylene encasement around the pipe and/or fittings etc. prior to concrete embedment, that additionally aids for more easy removal of the concrete from around the piping, if this were ever desired. If this is done for a main that is not otherwise polyethylene encased in the soil, it might further be a good idea to fasten the polyethylene wrap to the pipe out into the soil for at least a couple feet from where it enters/exits the concrete (I guess joint flexibility might also be a generally helpful in this same area if the encased piping were to move/settle relative to the rest of the buried piping, as I believe another responder has hinted).
Something sort of in between concrete encasement and soil embedment now available in some areas is "flowable fill", that is a poured or pumped sort of a lean mortar or concrete that claims ability to dig after cure but firmness practically better than many/most soils.
As far as mechanical vs push-on joints, both are well-proven joining concepts. However, the two most common brands of contemporary "push-on" joint seals (Tyton and Fastite) for ductile iron piping were invented in the 1950's (some decades after the old mechanical from the 1920's) as improvements to that older mechanical joining concept. While nothing is 100% trouble-free in universal practical application, I believe push-on or push-on restrained joints are in general even more reliable with current labor, as the field lubrication/bolting assembly/performance of mechanical joints is generally considerably more labor-intensive and labor-reliant than modern push-on styles.