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Butt Fusion Pipe Reliability

03/19/2015 1:18 AM

I've used the socket fusion method alot, its very reliable. Does anyone have experience with the reliability of the butt fusion method, either for gravity seqage lines or pressurized water supply pipe?

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#1

Re: Butt fusion pipe reliability

03/19/2015 4:27 AM

These days, most above-ground small bore sewage lines are in solvent-welded PVC, with the below-ground larger pipes in push-fit.

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#3
In reply to #1

Re: Butt fusion pipe reliability

03/19/2015 6:53 AM

Socket weld, of course. It gives the solvent much more surface to grab onto.

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#4
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Re: Butt fusion pipe reliability

03/19/2015 7:18 AM

I don't think he means solvent cement jointing. I've never heard that called socket fusion. Solvent cement joints (sometimes called solvent weld, in uPVC or ABS) are always socket types, butt jointing is not an option, as far as I'm aware. He means heat fusion welding.

Also I don't think uPVC is suitable for buried services, as implied by the OP. I remember 20-odd years ago Anglian Water (a water utility in UK, for anybody who doesn't know) telling me they had tried it and had lots of failures due to brittle fracture, and they had stopped using it. Not too surprising as it gets very brittle at low temperature. Whether later types, cPVC? are any better, or anybody has tried burying ABS, I wouldn't know.

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#5
In reply to #4

Re: Butt fusion pipe reliability

03/19/2015 7:24 AM

They don't use solvent weld for sewage underground here. It's all push-fit with rubber seals in plastic, and cemented joints in earthenware.

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#2

Re: Butt fusion pipe reliability

03/19/2015 5:00 AM

I suppose you're talking about PE/PP? I believe butt fusion is fine if done properly, you can cut through a finished joint and you can't see where the join is. Also you don't have to buy fittings, but it's harder to set up and use. So if you only have a few to do, better to go for socket fusion, but at a certain point (also depending on pipe size) it becomes cheaper to use socket fusion. That's my understanding anyway.

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#6

Re: Butt fusion pipe reliability

03/19/2015 7:59 AM

If you are talking about PE welding I have experience in butt welding and fusion welding. Butt welding is actually more reliable than fusion welding as long as it is done properly. You need the right kit and cleanliness is very important. Automated machines now apply the correct clamping force, hold time and cooling time to give a weld which is stronger than the pipe itself (so the company who trained me said).

I personally prefer butt welding as it is a neater finish and I have more faith in it. I have never seen a butt weld fail yet I have seen fusion welds fail. Other things to consider are that you can usually do fusion welding quicker, it is easy to do with little training (butt welding is a bit harder and you need more time to practice), and with butt welding you end up with a lot of ribbons of PE which are cut off to make the ends of the pipe flat. We were running 3 butt welding machines at the same time and you soon end up with lots of ribbons which blow around in the wind and can be an environmental hazard so must be cleaned up.

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#12
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Re: Butt fusion pipe reliability

03/19/2015 11:15 PM

I'm a little confused by the terminology being used there. My experience with PE pipe joints is that butt welding is a form of fusion welding, they are not 2 separate processes. We always called it butt-fusion welding as separate from electro or socket fusion welding.

Butt fusion welding requires more competence and costly equipment than does electro or socket fusion welding, the pipe sections must be the same wall thickness, cleanliness if far more critical, preheating of the joint ends and prevention of re-oxidation of the surfaces requires special care and equipment.

Butt fusion welding was the generally preferred method in our jobs where PE was used, but other methods were often employed for specific cases.

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#7

Re: Butt fusion pipe reliability

03/19/2015 8:13 AM

Repeating what's posted before, is this solvent welded or mechanically fused?

Butt joints are never a good choice in any adhesively joined system. The lap joint of a socket provides much greater joint strength and far better sealing characteristics. On the other hand, butt welds are a great way to join stainless steel supply pipes (sorry, the only experience I've had with plastic welding was a bit of a disaster....).

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#8
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Re: Butt fusion pipe reliability

03/19/2015 8:53 AM

I totally agree if you are doing PVC pipes. Sockets and glue is what I've used but I'm assuming this is poly-ethylene in which case butt welding is done with a machine which firstly cuts both ends of the pipe to a uniform flat surface then a hot plate is inserted between the pipe ends and the pipes are compressed onto the hot plate. This melts the PE and you see it form a bead. The plate is then removed and the pipe ends are pushed together with a given pressure depending on pipe size. There is then a hold period followed by a cooling period.

After this the bead can be shaved off leaving what is said to be a weld which is as strong, if not stronger than the original pipe. I personally don't know how it can be stronger but that is what I was told.

The fusion method is a prefabricated socket with heating coils built in. The pipes are inserted into the socket and an electrofusion box provides a current for a given period of time which essentially melts the socket and pipes together. The weld is confirmed by a small pin which pops out indicating the fusion has taken place.

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#9
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Re: Butt fusion pipe reliability

03/19/2015 9:41 AM

Thanks for the info!

I would think the extra strength comes from the thickened wall sections in the heated area caused by compression forces. Does it have a slightly belled out look on either side of the weld?

Also, you mentioned shaving the weld. How would you take care of excess material inside the pipe?

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#15
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Re: Butt fusion pipe reliability

03/20/2015 7:17 AM

I recognise what you are talking about as two of three methods used on HDPE.

Socket as you are mentioning with the coiled wire inside the sleeve or saddle fitting was a method I had to use in risky environments for risk of fire or explosion.

The company I worked for at that time also used a hand held welding extruder to join more unique and engineered constructions. These pieces were not rated for more than gravity flow.

A butt-fusion weld is the best option for joining HDPE in any environment, just keep it clean. The temp of the heater plate doesn't come back to me but the pressure used at the time was 75 psi by the area of the smaller surface in the joint.

In every pressure test I remember the pipe swelled and slowly ruptured outside the joining areas.

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#19
In reply to #15

Re: Butt fusion pipe reliability

03/20/2015 4:22 PM

I think you guys are getting your terminology very confused here.

Butt fusion welding uses the hotplate and then pressure joining.

Socket fusion welding does not use a special socket with a coiled wire, it uses a similar process to the hotplate except the heaters fit neatly over the pipe and inside the socket at the same time, then when sufficient heat has been applied, the heater is removed and the parts are fitted together.

Electro fusion welding is the one that employs the wired sockets, and it should NEVER be used in explosive environments.

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#10

Re: Butt Fusion Pipe Reliability

03/19/2015 11:21 AM

We use a very large amount of HDPE pipe at all of our sites throughout the world and we use the low-cost method of butt fusion 99% of the time.

We experience a high number of butt fusion failures daily throughout the systems with the fusion company being blamed for the failures.

It is difficult to determine the exact cause of failure however most of the failures appear to occur in the pipe wall next to the fused joint and not the actual fusion bead.

This leads me to believe that the failure is occurring due to the HDPE material immediately adjacent to the fusion sight being crystalized from the excessive applied heat which may be exceeding the material temperature rating.

This may be due to operator error however there are a lot of our fusing machines that do not have an adjustable temperature range.

The socket fusion connections seem to only fail if abused by equipment contact or mishandling of the pipe.

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#11

Re: Butt Fusion Pipe Reliability

03/19/2015 12:20 PM

When doing a butt weld it is vital that the ends of the pipe are clean. We had a tent which we would erect over the equipment when working outside. If any contaminant gets on the surface it can lead to a weak section as it can be pushed inside the bead.

The machines I used had adjustable temperature plates. Again it was very important the correct temperature was used.

I agree the weld would be stronger than the pipe if the bead was left of but if it was removed there is no extra thickness. As a side note if you want to imagine what the bead looks like think of melting a solid plastic rod against a hot plate and pushing it while it melts. The edge curles back and forms a fairly uniform ring (kind of like the shape of an o-ring on a rod). When the two pipes are fused together it looks a bit like a letter B in cross section.

To remove the inner bead there is a device which is pretty much like a stanley blade mounted in a device which sits on the end of a pole. You have to feed it in from the open end then rotate it round to cut the bead off.

The butt welder machine also digitally logs all the details of the weld (temperature of the plate, clamping force, hold time, cooling time etc.) so there is traceability. I spent 6 weeks working 7 days a week with three welding machines doing 10 hour shifts (don't know how many welds in total but a lot) and we didn't have 1 failure.

I then found a guy in another part of the company doing fusion welding with no training and out of 4 welds 1 failed. He wasn't even cleaning the sand off the pipe! So I guess it all comes down to who is doing it and if they have any idea what they are doing.

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#13

Re: Butt Fusion Pipe Reliability

03/20/2015 6:02 AM

So if butt fusion is done right by trained ppl with the right tools (adjustable plate temp, digital logging) it works ok. otherwise, socket fusion (by heat not by solvent) is more error-proof.

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#14
In reply to #13

Re: Butt Fusion Pipe Reliability

03/20/2015 7:00 AM

Agreed, that sums it up. Pretty much what I said in #2

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#16
In reply to #13

Re: Butt Fusion Pipe Reliability

03/20/2015 8:30 AM

Butt fusion of PE pipe is great only if you use Driscopipe. Trust me, I know about this.

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#18
In reply to #16

Re: Butt Fusion Pipe Reliability

03/20/2015 3:44 PM

I have done a lot of butt fusion joints with HDPE pipe and when it is done properly the pipe is welded and as strong as if it were all one piece without a joint. You can also socket weld HDPE with a socket fitting which has a wire inside it to fuse the pipe. The socket weld is stronger that the butt weld due to its increased thickness. Butt Fused HDPE can be used in a pressure pipe application like a water distribution system and is good up to the rating of the pipe. HDPE is also good for heat up to 150 degrees F.

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#17

Re: Butt Fusion Pipe Reliability

03/20/2015 9:27 AM

Very very reliable for domestic water, fire water, gravity sewer, pumped discharge or natural gas. I have used this in each application. Smaller bore pipe is usually socket fusion construction with the larger bores butt fusion. It is a different process in the pipe face preparation. The vendor for the material will more than likely also have the butt fusion pipe machine as well for rental. Most of the machines now are computerized and are user friendly. If your crew is unfamiliar with the process, the material vendor will need to certify the installers. That is usually done on site or at their shop and they go through the proper fit up, bead roll and operating the equipment. Your installers will then get their butt fusion "card" and add that to their resume.

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