Flanged connection for underground piping

[FilippoT]

We have been required to install CS piping (fire water) underground with flanged connection to avoid hot work inside a living plant. Is there any requirements for buried flanged connection like a dedicated pit for bolt access?

 

[LittleInch]

It's never good to bury flanges, but if you have to then you can bury in a box, but this often fills with water and dirt or you can add flange protectors to seal the internal gap between the flanges. Use corrosion resistant bolts and buts and coat the finished flange as well as you can. Better still use PE pipe for buried fire mains"

My motto: Learn something new every day

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

 

[zdas04]

I bury flanges all the time. There is some concern about the flanges acting as an anchor point that will increase stresses. Caesar II doesn't show that increase as big enough to be a concern, but people intuitively "know" that it must be.

There are caps you can buy that are full of grease to protect the studs so the nuts will come off. They work, but add a lot of expense to the makeup. Without some serious protection you won't be able to get the nuts off the studs after just a few months and will have to scarf them off with a torch (probably more hot work than just welding them in the first place).

Setting a valve can for a flange creates far more problems than it solves.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[LittleInch]

For a fire water system which is low pressure, won't see much temperature change / stress and if it leaks a little bit after 10 years then no one really cares, it is fine to bury as is, but it is good practice to try and protect the inner flange faces from corrosion, but I wouldn't bother with a pit or similar tunnel / tube affair.

As said I would have thought that there were better materials for a buried fire main, but that's a different question.

My motto: Learn something new every day

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

 

[zdas04]

Fire water systems are generally in the ANSI 150 range of pressures. Too high for HDPE for the most part. HDPE lined CS is pretty common. For lines 8-inch and smaller, the RTP products make a ton of sense. Corrosion in firewater systems have two important consequences: (1) corrosion products can block lines; and (2) corrosion leaks can steel capacity to the point that you have inadequate delivery. It is really easy to treat these systems as "secondary" or "not important, should be done on the cheep", but that is nearly always eventually a bad choice.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[LittleInch]

I've put 16 bar rated systems in for fire water - very easy to lay and connect and forget about. Straightforward CS is not normally seen as a great idea as noted in zdas04's note above.

My motto: Learn something new every day

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

 

[RossABQ]

Are Victaulic couplings an option? Very common in this kind of work.

 

[rconner]

The National Fire Protection Association (NFPA) has a standard NFPA 24 Installation of Private Fire Service Mains and Their Appurtenances that discusses to some extent piping and joining requirements. While it would be advisable for you to refer to this extensive standard yourself, I understand allowable buried main piping materials, that have traditionally included widely used cement mortar lined ductile iron piping, now also allow coated and somehow lined steel pipe for even buried service, as well as some plastics and others, but steel piping et al is required to be and "listed for fire protection service". Steel flange standard AWWA C207 is referred to in the standard and/or appendices, as is AWWA manual M11 for steel water piping. I do not think flanged joints are excluded, except perhaps at those locations where piping passes under foundations etc.; however, I know referenced AWWA manual M11 does have some comments under a section "Good Practice" that states, "Flanges are commonly used to join steel pipe to valves, meters, and other flanged accessories", followed immediately by the statement, "Thermal stresses may be a consideration, and these can be accommodated by sleeve couplings, grooved-and-shouldered couplings, special welded joints, or expansion joints..." as well as similar potential needs for flexibility near welded flange outlets or nozzles.
I guess I would only add that flanged piping on paper is basically just straight and really allows for conforming to unanticipated changes in (mis)alignment, cover, non-uniform support/settlement, or beam loads etc. by stressing the pipe and gasketed joint. I noticed a few years ago BigInch on the Pipelines.... forum wrote,

“All flanges are a necessary evil. Sometimes the evil is above ground, sometimes below. Wishing away the evil usually doesn't work.” BigInch 2011