Mechanical Joints Above Grade 3

[riverhound]

Hi, I have been asked by a supplier to subsitute some flanged fittings for mechanical fittings in an above ground application due to timing/supply issues. The piping material is C900, so a mechanical restraint would have to be used in either case (like EBAA Iron or other). The piping would be supported by pipe hangers. Does anyone have experience with mechanical fittings above grade and know of any advantages/disadvantages.

 

[civilperson]

Most all fire water building stations use exterior above grade pipes and valves, (from subgrade water mains). Usually in the 4" and 6" sizes with flanged fittings.

 

[bimr]

The need for flexibility in buried piping is one of the advantages of mechanical joint fittings. Flanged fittings, are mainly used for inside installations where restraint is needed and where future modifications may be necessary. Flanged fittings are seldom used in buried services because rigid joints can shear.


Perhaps these notes will help:

http://www.acipco.com/adip/specials/span.cfm

http://www.ejprescott.com/products/water-sewer-drain-fittings.php

 

[SteveWag]

I see more and more contractors asking to use M-J fittings rather than flanged or Victaulic connections. M-J connections can be done in-the-field with no prior planning or delivery lead time. I try to enforce my design standards and won’t allow M-J as replacements for Victaulic, but on small jobs/small contractors sometimes it’s easier to allow the use of M-J fittings instead of flanges. The lead time for flanged pipe is only a couple of days here in central PA, but if the contractor cannot lay out the piping accurately these days add up. I don’t think M-J fittings, with joint restraints look very good, but they do work OK.
Steve

 

[rconner]

Just a couple comments. I don't think it is unusual to see some "mechanical joints" in piping systems "above grade", but use of plastic pipe in general in at least some above grade environments may well be another subject/and with other concerns (for whatever it is worth I sort of understand the problem as I don’t think there is even any mention of aboveground or above grade or flanged joints etc. in the “C900” you refer to, and the scope of this standard at least at one time specifically used the word “underground”).
With regard however to the basic piping question of a direct substitution of a mechanical joint vs a flanged joint (the latter with innate bolt “restraint”), there could be concerns as well depending on the specific design of restraint to be used to keep the plastic pipe end from pulling or deflecting out of the socket.
Also, (as I think at least intimated in bimr and SteveWag's good responses) a standardized mechanical joint for a fitting or valve has a socket depth or "stab length", wherein the pipe typically penetrates some distance up into the socket (I think up to about 2-1/2" deep on smaller pipe sizes, and deeper on larger). Unless the fitting is a mechanical joint sleeve, the pipe can therefore not be as easily lifted or withdrawn laterally from a line, even after complete unbolting of the joint, as can a flanged or grooved coupling pipe , say in piping/valving etc. replacement, re-routing or maintenance operations etc. e.g. as by very slight spreading apart of the flanges etc.) In other words the pipe end up in a mechanical joint can hang up on the penetrated socket end. This behavior may or may not be a future problem in the specific piping configuration/application, with sometimes other flexibility.
I will note also there are other sorts of devices available in the general piping field including e.g. "flanged adaptors", some of which offer a basic field-adaptability (cut to suit), a mechanical sort of sealing mechanism not unlike mechanical joint on one end with a flange connection on the other, and some even offer separate restraint features as well as more easy lateral pipe withdrawal features. Again however you might want to contact the manufacturers involved to make sure they are happy with use of these devices/restraints etc. with the specific above grade plastic piping application.

 

[riverhound]

Thanks for all the responses!