HDPE Welding - ???? - SailNet Community

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  #1  
Old 10-26-2011
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HDPE Welding - ????

OK - I don't know what I am talking about, but my friend asked me about this. He wants to make some kind of "boat tank". He says:
I have access to a material called HDPE (High Density Polyethylene) and was wondering if you know how to weld this?
Any answers for him?

Many thanks

Rik
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Old 10-26-2011
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There is such a thing. In my area, Maritime Plastics is capable of doing it. However, it seems rather unnecessary for your friend. The Forespar website has a slew of tanks in all sorts of shapes, and volumes.
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Old 10-26-2011
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There are also adhesives for HDPE, but not commonly found in the hardware store. Some RV supply stores have HDPE adhesives because many RVs have this type of roof. HDPE is common on the roofs of commercial buildings. Be careful with these adhesives as some people have an allergic reaction to them.
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Old 10-26-2011
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I have done several repair welds with it and I have not found it to be very easy. Many people compare it to tig welding but I find it to be much harder. I would not want to try to make my own tank out of it but repairing a small crack in an existing one isn't bad.

There is a decent amount of information on recreational welding of polyethylene from whitewater kayakers. They tend to crack their boats a lot and need to do a lot of repair. I have welded quite a few kayaks and there are huge differences in how the plastics behave even though they are not that different.

My opinion would be that unless your friend is a professional tig welder, this would not be a good project to try.
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Old 10-26-2011
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Check out uretbane supply dot com; they'll have everything you need along with good info on all plastics
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Old 10-26-2011
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There are plastic welding guns that will do the job, and special adhesives. West System "G" epoxy might be one of them now.

But welds are still seams and seams still leak. You need ten years as a professional welder before oil companies will even interview you to weld pipe, that's how hard it is to make seams that don't leak.

And that's why seamless rotary molded tanks are the norm on boats. If your friend wants to weld up a plastic tank because he's got some cheap plastic stock, tell him to buy the mop first, because he'll need a cleanup sooner or later unless he's one extraordinary fine welder.
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Old 10-26-2011
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stop by a ski shop that has a service dept. They will have a plastic welder for ski bottoms. Very easy to do.
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Old 10-26-2011
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incredible anwsers given here! I have been welding anything that can be welded for 40 years. yes you can weld HDPE. Welding with a hot air gun is the best way and works a lot like welding steel with a gas torch. they do have electric plastic welders but they a limited on the size of the bead. the hot air equipment is very expensive. the welds are only about 50% of the strength of the parent metal. making a tank this way would be very difficult and very expensive. they do have adhesives for HDPE but they do not like to stay stuck to the material if it is flexed, also not good for a tank
as for HPDE being used for roofing. I believe it is EPDM that is used for covering a roof and is glued together, however they do make ( GREEN ) roof shingles out of recycled HPDE.
As for needing ten years before welding for the oil companies, some one should tell them that. My son is 22 and welds Gasoline pipe line for an oil company. all you need to do is know how to weld and have all the proper certifications for the welds that you are doing. what that has to do with a plastic tank I do not know.
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Hot Plate for HDPE

Tes HDPE is weldable. Full strength joints are achieved in pipelines. These are the black poly pipes you see. A spexial hor plate is used with axial clamps to apply pressure. The joint is a solid state weld and you can see the expelled material at the weld joint. (No melting or fusion)

I've made (fabricated and welded) HDPE tanks for acid and chemical use. HDPE is a low strength material so it needs to be well supported so that the tank load is not carried by the flat sections of the tank.
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Old 10-26-2011
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Harbor Freight has "torches" for welding HDPE; not terribly expensive. I've done a bit of HDPE welding, many, many years ago. It isn't really all that difficult, but it does take a little practice. Most of what I did wasn't so much fabricating stuff as it was repairing/modifying stuff (fixing leaks and installing bulkhead fittings on large tanks/aquaria/filters, that kinda stuff).

HDPE has a lot of advantages. It's light, fairly easy to work with (with the right equipment), and almost completely inert, although it does absorb hydrocarbons a bit. However, if I was going to fabricate a tank, I think I would use epoxy and plywood to make a stitch and glue one. Plywood is much stronger, and stitch and glue seams are much less likely to be "weak spots" than in any welded HDPE tank. Also, depending on the resin one uses, epoxy can be even more resistant to fuel or water than HDPE. It's probably cheaper to build a stitch a glue tank, since you don't have to buy any specialized equipment.
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