HPPE pipe specifications and welding info 3

[wunderjah]

I am currently designing 3km's of Rising main - yes way too long!!, and need info on using HPPE pipes and how you go about jioning/welding, laying them - as the contractor hasn't used them b4!!!!

 

[Ussuri]

There are two main methods of joint MDPE, HPPE pipes. One is electrofusion, the other is butt fusion.

Electrofusion is the easiest. Basically the two pipe ends are slotted in to a special collar. The collar has a filament embedded in it. An electric generator is then connected to the collar and a current passed through it. This fuses onto both ends of the pipes and gives you a joint. Its a very easy process.

Butt fusion is more like welding-ish. The ends of the pipes are fitted into a machine which 'melts' the ends and then forces them together. This produces excess material in the inside and out which has to be reamed off as it reduce the cross sectional area of the pipe. The benefit of butt fusion is you dont have a collar so it keeps the OD constant.

http://www.wavinpdfs.co.uk/pdfType.asp?id=6

click on the link for polyethelene water systems technical guide. This is a very useful guide.


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Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.
Archimedes

 

[wunderjah]

thanks for the reply,
Is there any difference in the type of welding or method, for Water mains of foul sewer rising mains. If so does anyone know the Standard in Ireland or the UK?

 

[Ussuri]

Not to my knowledge. The jointing process is the same. The pipework you use will be a different colour, blue for potable water mains and black for all other non potable uses.

General standard specification used in the UK is CESWI (Civil Engineering Specification for the Water Industry). There is also Sewers for Adoption (in England) or Sewers for Scotland (in, strangely enough, Scotland). These documents spell out the design requirements and specifications that private developers must work to if they wish the water authority to take ownership of the asset at completion. They are a lot more stringent.

With regards to jointing you should look at Water Industry Specification WIS 4-32-08 Specification for Site Fusion Jointing of PE80 (MDPE) and PE100 (HPPE) pipe and fittings. Some are free, some you have to pay for. Unfortunately WIS 4-32-08 is one that requires cold hard currency.

http://www.webookshop.com/asp/publications.asp?Page=1&idDepartment=3

BS EN 805:2000 Water supply. Requirements for systems and components outside buildings is the relevant Euronorm. I cant remember the one for wastewater though.

Another good reference is the Pipe Materials Selection Manual published by the WRc plc.

 

[StephenA]

The electrofusion couplings cannot be used for the larger sizes.

Flanged couplings can also be used but as PE creeps they generally eventually leak. However there is a coupling called Aquagrip which will give you a leakproof joint. They tend to be expensive.

The removal of internal beads is usually done as soon as the weld is complete and before the PE has cooled down, so removal is quick. The trick is to get the welder to recover the beads, then you know whether he has cut them all off!

Pipelife also has some good downloadable brochures on their website

 

[jdonville]

Numerous resources are available from the PE pipe manufacturers websites.

The following link:

http://www.isco-pipe.com/products_services/pipe_joining.asp

features animated illustrations of several of these joining methods, although their service area is generally the continental USA.

Have you tried to Google/Yahoo "electrofusion" or "joining PE pipe"?

Jeff

Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.

 

[wunderjah]

Another Question,

Does both Elctro Fusion and Butt Fusion withstand high pressure pipes? Or does they also need Thrust blocks etc??

 

[Ussuri]

Both jointing methods, when done correctly, will be as strong as the parent material. So the will be able to resist the pressure in the pipe. PE pipes are not for particularly high pressures though, max 16 bar.

Because PE pipe is a welded, or flanged/welded system. Pipeline thrusts are resisted by the longtitudinal stresses within the pipe wall, transferred the joints (welded or bolted). So in general thrust blocks are not needed at bends or branches.

On smaller diameter lines compression fittings are used to joint pipes. I am not sure whether these fittings are sufficiently robust to thrust.

 

[jdonville]

Ussuri,

I worked (resident engineer) on a 4-inch ductile iron force main once (sanitary). We used MJ couplings to attach the 45-degree bends near the lift station. Thrust blocks were required at each of these 45's.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.

 

[Ussuri]

Jeff

In my experience you generally need thrust blocks on DI lines unless they are fully flanged all along their length. If the pipes are spigot and socket they will be forced open by internal pressure even if you have flanged sections at the bends. The load is just transferred to a point which isn't restrained.

MJ couplings do not provide in-line restraint hence an external restraint is required (thrust blocks). The are basically band seals which seal one end of a pipe to another.

 

[BarryEng]

DI pipe thrust - look at the web site for DIPRA (ductile iron pipe research assoc) of the USA. They provide a program for calculating the length required (for thrust restraint) so that thrust blocks are not required. The theory was developed in about 1976 & has been in use since that date by DIPRA.

The pipes are 'harnessed' by using special joints for the required length. In Australia, a TytonLok joint can be used (Tyco DI pipes) & in the US there are several manufacturers of restrained joints. The thrust force is taken the same way as for piles (but in a horizontal direction), by using a combination of both skin friction (around the pipe) & end bearing (of the pipe & fitting).

Be careful about using AWWA M11 - steel pipe design & installation (& the Tyco manual in Australia), because they use an anchorage length virtually based on the vertical mass times the coefficient of friction. This is not representative of 'true' anchorage because it only takes into account 'shear box' type of friction. This is not how a pipe anchorage resistance is developed. The result will probably be several times the length calculated by the DIPRA method. The DIPRA method has stood the test of time.

To Ussuri
In the water industry in my country, flanged joints are used VERY rarely on pipelines except for valves (& even then they are installed with a rubber ring dismantling joint). Even bends are RRJ. The water industry does not like many items that can corrode such as flanges, bolts & nuts. A flanged joint (or pipe) is more expensive, takes longer to put together, & is a source of corrosion.

Flanged joints are used on bends for above ground situations (pump stations & bore heads etc) because they allow not only easy dismantling, but can be replaced without disrupting the pipeline.

BarryEng

 

[Zambo]

Ussuri,

is it always required to remove the beads produced by butt welding. As coils come in up to 50m lengths for 125mm diameter and 12m lengths for larger diameters access would be a problem. I would think that the beads are no bigger than the root weld of steel pipes

 

[Ussuri]

Zambo

I think it depends on circumstances. The bead may be around 3mm for a 63mm pipe and up to say, 5 or 10mm on a 250mm pipe.

There are schools of thought that say they have absolutely no effect and can be left. There are other schools of thought which believe they cause turbulence, reduce flow and cause gunk to build up.

Removing them can be a pain in the derriere, and I'm not even sure you can remove them from coiled pipe as it's just too long. There might be a pigging system that does it but I have never come across it.

I guess the simple answer is it's a judgement call. For example, I wouldn't worry about it on pumped water mains but would on smaller bore gravity sewers. Then again if the spec/client says you do, then you do.