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Tie in installation into existing 8" main
4

Tie in installation into existing 8" main

Tie in installation into existing 8" main

(OP)
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

RE: Tie in installation into existing 8" main


dbelov72,
"The contractor claims that freezing is technically possible on an 8" pipe"
What exactly does the "Contractor" mean by this. In my opinion (based on some experience) freezing the main line would be the same as shutting it down.

I suggest you consult with one or more experienced and qualified "Hot-Tap" Tie-in specialist contractors to see if there are alternatives to solving your problem.

Specifically ask them about "Stoppling" method of adding a Branch with out shutting down the main line. It is a valid potential solution.

Sometimes its possible to do all the right things and still get bad results

RE: Tie in installation into existing 8" main

I presume someone has already done the hydraulics to ensure you don't starve the current water users.

There's no reason a hot tap cannot be done without a shutdown, especially for water service.

Stoppling is more for cutting out and removing a section of pipe while the line remains in service.

Piping Design Central

RE: Tie in installation into existing 8" main

(OP)
thank you for the informative replies!
just wanted to give you some details on what happens.

so, the hot tap would apparently be the most reasonable solution ever.
however, the it is the main pipe, made of ductile iron pipe.
by drilling the pipe, which is what hot tapping does, would bring a contaminant into the potable water flowing through the pipe.
this is the explanation from the contractor.
my mistake here was that I didn't mention the type of pipe and the fact that it is potable water that flows through it.

Also, for the freezing part: shutting down the water would not be possible for extended period of time (the facility I am working on right now is an airport). it technically could be done at night for couple of hours; however, draining would take a while...therefore, freezing two points and working in between would also be an option. the contractor said this option would not impress us in terms of pricing (I am still intending to get the pricing for this).

The option that everything is boiling down to is to bring the water into the washroom by tieing in to a branch pipes from another washroom. supposedly, the supply of water is enough. however, this option requires a hell lot of piping (almost 20 meters...) which motivates me to look hard for other options.

Thanks a lot!
One of the many big reasons I like engineering is engineers, people who know what they talk about. working hard on becoming one!

RE: Tie in installation into existing 8" main

First of all, what size water supply do you need? Second, small service taps are made 100's of times every day. Third, there is no contamination of the original supply because the tapping machine is pressurized by the supply line and is opened to install the tap and corporation cock.
fourth,If you contractor doesn't know how to do this, hire a different one. 20 meters of pipe is not a lot, 2000 meters is a lot.

Richard A. Cornelius, P.E.
WWW.amlinereast.com

RE: Tie in installation into existing 8" main

I think the "contamination" refers to cuttings/shards (not the coupon itself, of course) potentially falling into the run pipe and continuing in the flow to downstream users.

Piping Design Central

RE: Tie in installation into existing 8" main

dicksewerrat is correct.

The hot tap procedure includes disinfection and flushing of the water main, Any certified water operator should know the procedures required.

Refer to the attached typical procedure. Note the reference to the AWWA standard. You might consider emplying a more qualifed contractor if this is a critical issue.

http://dnr.mo.gov/pubs/pub2442.pdf

Hot taps are frequently done by third parties. Hot taps are common procedures and done every day by potable water system operators.

RE: Tie in installation into existing 8" main

These are usually called wet taps instead of hot taps when used for potable water or sanitary force mains.
This is a very common procedure and I would be leery of any contractor who was not aware of it.
I still have the coupon from the first wet tap I observed.
Plus everything bimr and dicksewerrat said.

RE: Tie in installation into existing 8" main

(OP)
Just a little update on the topic.

So I ran the meeting today with everyone, us, the general contractor, owner representative, consultant, mechanical contractor.
Presented the following solutions:
1. Replace the section of the pipe
2. Hot tap
3. Freeze the thing and perform works
4. Tie in from a different (remote) location

The discussion fairly quickly boiled down to hot tap.
Client's concern was that the ductile pipe is not repairable; therefore, it is a contaminant. He then was explained that it is a super tiny contaminant that should not cause any stress.
His other concern was that they had a hot tap on a PVC pipe; the coupon got sucked in by water into the pipe. Although it didn't cause any negative consequences, the owner still thinks bad of hot taps.

The whole story was an interesting learning experience, especially for myself, who is a civil with an interest in mechanical.

Thank you everyone for your replies!

RE: Tie in installation into existing 8" main

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

RE: Tie in installation into existing 8" main

Is this on the water service (upstream of the backflow prevention) or on the domestic water piping.

I cannot speak about the water service - they do things differently than the domestic system.

if you to a wet tap, the procedure to disinfect and flush the system will require lots of water being wasted (the entire system), given that the system is not being taken out of service.

If this is on the downstream side of the backflow preventer, the applicable portion of piping needs to be taken out of service, drained, disinfected and flushed. this can be accomplished by also installing small drain cocks on the piping and using them as entry/exit points of the fixed system.

Talk to the plumbing inspector since he will be the one approving the work.

RE: Tie in installation into existing 8" main

(OP)
possibly it didn't attach itself to the drill properly

RE: Tie in installation into existing 8" main

Actually, the 20 meters of pipe is probably less expense than the cost of the hot tap. 20 meters of pipe is just a little pipe, not "a hell lot of piping (almost 20 meters...)".


RE: Tie in installation into existing 8" main

I don't see any "wires that hold the coupon on the drill bit" in bimr's photos.

Piping Design Central

RE: Tie in installation into existing 8" main

(OP)
bimr,

If it was, we would totally go for that option, I wouldn't search for other solutions, and we wouldn't have that meeting.

Although, it sounds simple and looks easy on the drawings, this is what happened:
The 20 meters of piping need through different rooms, that contain mechanical equipment (baggage conveyors). It is hard to go through those rooms, since it is very very tight; how they wanted to install pipes in there, I still don't quiet imagine.
Pipes go up and down, they need to be cut, since they are supplied originally way too long; thus, there is a whole bunch of elbows, reducers and other things. The submitted material thing itself included an entire A4 page of things that need to go in there; therefore, we only got material cost for $25000. Plus, there is a labour cost, which is 60 manhours in best scenario... Lockouts, scaffold, defects - all this stuff has indirect costs in it as well.
In contrast, hot tapping takes only to get the machine up to the pipe, get the saddle on, drill the thing, and get it working. $3000 tops.

RE: Tie in installation into existing 8" main

Understood. Looks like your biggest problem is project management ie. herding all of the cats.

RE: Tie in installation into existing 8" main

Ah, OK, the spikes.

Piping Design Central

RE: Tie in installation into existing 8" main

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.

RE: Tie in installation into existing 8" main

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.

RE: Tie in installation into existing 8" main

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.
WWW.amlinereast.com

RE: Tie in installation into existing 8" main

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

Richard A. Cornelius, P.E.
WWW.amlinereast.com

RE: Tie in installation into existing 8" main

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.

RE: Tie in installation into existing 8" main

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....

Quote (jgailla)

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.

RE: Tie in installation into existing 8" main

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=G1tcLwWKtOQC&... . 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...].
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-free... , http://www.nitropipefreeze.com/tag/liquid-nitrogen... and http://www.hottap.com/recent_pipeline_jobs_complet... 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.

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