Tie in installation into existing 8" main 4

[dbelov72]

Hello everyone,

There is an 8" pipe through which domestic cold water goes to the entire facility, which is an airport.
We need to tie in a massive washroom to it; however, we can't really shut down water for too many hours...

One of the alternatives is to tie in to another washroom, but that adds to costs way too much in the form of piping.

What could be the other options for that to consider?
The contractor claims that freezing is technically possible on an 8" pipe; however, it seems to cost a fortune...


Regards,
Denis

 

[LittleInch]

debeov72

A few points / comments from me for this and possibly for the future.

Maybe it's me, but the term "hot tap" usually means that the split tee or saddle used is welded to the main pipe. For ductile Iron I would normally think that a mechanical bolted split tee is more likely due to the issues of welding ductile Iron, hence more of a "cold tap"...

Bimrs cutting from the press is a little gushing = TDW are very good and experienced at these things, but the usage is hardly "revolutionary" or "rare but growing". The systems have been around for over 50 years and used frequently all over the world.

The option to freeze looks to me to be questionable when using Ductile Iron. Sure it's better than cast iron, but you end up with some seriously low metal temperatures and a significant amount of force from the freeze plug. The risk of a sudden crack during this process would seem quite high to me, but maybe it's been done lots of times - I'm more of a steel and PE pipes man.

Yes you often get a small amount of debris entering the flowing stream, but only rarely do you loose the coupon. I suspect with PVC it maybe broke up during the cutting operation or when only a small section was left. If you press too hard with the cutter you can cause this to happen as the last section is cut.

I don't believe you've said how big your tap is. The smaller the easier it is.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

The terminology for "hot tap" probably derived from the "hot work" terminology or vice versa. It just means that one is working in an energized environment. Water operators call them wet taps.

 

[dicksewerrat]

Freezing water lines is a bit dangerous depending on the freezing medium. With an 8 inch line you would need a very large amount of dry ice and ventilation for the wok force. If using a freezer blanket, it also would have to be very long and on both sides of the " cut'. I once pulled up a job and they were using a propane tank turned upside down to get the liquid propane to flow. I called the Fire Dept. They had many issues with the contractor.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[dicksewerrat]

I still don't know what size line for the supply.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[rconner]

The premise of this situation has sounded a little strange to me. Difficulties encountered tapping pvc pipe should not influence designing operations for ductile iron pipe - the pipes are different animals. Actually also, with a good crew and equipment it often also doesn't take much time (depending on locations of valves and dewatering etc.) to expose, dewater and even cut/sleeve/bolt in a tee and any new valving as desired at a future lateral connection in ductile iron piping (as a rough rule of thumb, a cut in ductile iron pipe with an abrasive saw might take something on the order of a minute per diameter-inch to accomplish). If one doesn't know what or where sources of axial thrust may be away from the pit, it is probably however a good idea to take just a wee bit more time and set some wedges for restraint e.g. of good quality retainer glands on the sleeve and all otherwise unrestrained mechanical joint connections. [And It sure doesn't take much time for experienced crews to make a wet tap in ductile iron piping -

https://www.youtube.com/watch?v=0IWqlevxKKw

;>) ]
All have a good weekend.

 

[jte]

I tend to agree that hot tapping (ok, wet or cold tapping) is likely a good method in this case. However, a pair of freeze plugs can work as well. Just depends on the circumstances. A bit of guidance for freeze plugs can be found in ASME PCC-2 Article 3.2. A story of how one was used for a water line in an oil refinery context is in the August 2011 issue of Mechanical Engineering magazine. If you are an ASME member with a login to asme.org you can read the article at

http://www.memagazinedigital.org/memagazine/201108#pg46.

That doesn't sound right. How can a pressurized pipe suck a coupon in?

Simple enough. The pressure in the carrier pipe and the hot tapping machine equalize as soon as the pilot drill punches through the carrier pipe. This happens prior to the initiation of cutting the coupon. [Picture a standard hole saw for a drill: The pilot hole penetrates before the saw part starts its work.] So pressure is out of the picture and we are left with flow turbulence. With a high enough flow, this could break the coupon off the retaining device on the pilot bit. I also supported a job in which the hole was cut without incident, but the cutter blade and coupon were left behind. Oops.

 

[rconner]

I have nothing against pipeline freeze plugs; however, I have read the section talking about same in the reference at

https://books.google.com/books?id=G...nepage&q=freeze plugs embrittle pipes&f=false

. While of course all types of construction operations need to be done safely, and the following are certainly not a bar to all utility when wielded by very competent folks, freeze plugging appears to have some rather unique hazards. While they are not necessarily the problem most lay folks would fear (i.e. outward expansion splitting a pipe) , there is however no question e.g. a lower than -300 F. temperature of liquid nitrogen will at least temporarily embrittle any piping material, the cooling mediums will in effect destroy human flesh(maybe not "burn" in the conventional sense, but something resembling it) if accidentally and/or carelessly released, and they can also be an asphyxiant without adequate ventilation. [I don't have access to the ASME reference that was provided, but I have seen the NRC take on this subject at

http://www.nrc.gov/reading-rm/doc-collections/insp-manual/technical-guidance/tgfplugs.pdf

].
All that being said, I have heard of this being done with similar sized ductile iron piping e.g. at

https://www.youtube.com/watch?v=kt2Gyz-GOTg

,

http://www.nitropipefreeze.com/blog/8-ductile-freezing/

,

http://www.nitropipefreeze.com/tag/liquid-nitrogen-pipe-freezing/page/3/

and

http://www.hottap.com/recent_pipeline_jobs_completed.php

etc. and haven't happened to hear yet of problems with that pipe.
I would have one other at least theoretical concern if the main is kept under pressure and composed of any piping material with unrestrained joints in the area i.e. when a cut out beyond a freeze plug is attempted. In that case it could be that there could be a very large (i.e. "bulhead") thrust force, supported then with really nothing but air, that could conceivably jerk unrestrained joints loose down the line.