Welding of plastic tank

[skatun]

So I got this nice 100L plastic diesel tank, however it is 10cm to long. Is it possible to shorten it? Like weld it back together and use the left over material as welding material?

https://www.maritim.no/dieseltank-55-liter

[Singularity]

Thinking out loud...
I think it's possible, but to summarize much, if it's possible, I assume that it would only be cost-effective if done by a plastics expert close to you. Thus I'd try to find a local plastic welder and see if they can more precisely guide you.

I personally wouldn't do this as a DIY and would only let a local guy do it if they did that kind of work on a regular basis. Way too much mess and trouble if it later leaks.

[model 10]

You would need to be pretty good. Maybe start with it long and keep cutting off your screw up's. Then you would need to weld on a doubler over the entire weld because no way would the weld hold 3psi without the extra layer.

[john61ct]

Yes it is possible.

By a professional.

DIY, I would determine precisely which low-energy plastic it is, buy the right gear, find a lot of scrap bits and practice practice practice.

At the same thickness before starting on your actual tank.

Oh and I imagine it would need to be pretty spotless before you start too.

So, no. 8-D

[thinwater]

You need to talk to the maker. It is a roto molded tank, and if it is low permeation it either has a thin liner boned on the inside or has been doped with solids that decrease permeation. Either can make welding difficult or impossible. At least that would be the case in the US, but I can't read the specs.


The tank will also no longer be certified. Granted, this is not always legally required for diesel, but the insurance company may feel differently.



It's not a water tank and the material may be different. Proceed very carefully. Personally, I doubt it makes any sense.


(Licensed API tank inspector)

[Marc1]

Short answer is no for a boat fuel tank ... if you want it for a horse drinking tub I say give it a tray

[Compass790]

I'd ask the manufacturer

[ventura 38]

i welded a lots of snowmobile gas tanks that were made from polystyrene. i used coffee can lids worked fine held up for years

[deblen]

If your tank is polyethylene plastic,find the nearest salmon aquaculture welder. Norway pioneered floating poly cages.


Edited -wrong link.
Now I can't upload a pic of a salmon aqua. site,but you can google local suppliers. / Len

[thinwater]

Originally Posted by ventura 38

i welded a lots of snowmobile gas tanks that were made from polystyrene. i used coffee can lids worked fine held up for years

a. Polystyrene melts in contact with gasoline. I assume they were polyethylene. But new low-perm HDPE is not the same material. I'm guessing it is also a croslinked version, which is different.


b. Would you use a poly tank that had been wleded in that manner in your boat?



By the way, the welded poly tank companies will no longer touch fuel or gasoline tanks. You have to either find a shape you can use or go with metal.

[Cheechako]

It depends on the type of plastic. Linky no worky for me.

[deblen]

Originally Posted by thinwater

a. Polystyrene melts in contact with gasoline. I assume they were polyethylene. But new low-perm HDPE is not the same material. I'm guessing it is also a croslinked version, which is different.


b. Would you use a poly tank that had been wleded in that manner in your boat?



By the way, the welded poly tank companies will no longer touch fuel or gasoline tanks. You have to either find a shape you can use or go with metal.

I don't know what "breed" of polyethelyne that is used to make red & yellow jerry cans,for gas & diesel-but it must be the same poly as used for common black poly well pipe & has been welded for years by local cage makers. I have a Wedco poly dinghy (1976) still in good shape. I had some poly brackets & stuff welded to it for convenience. The locals have built complete workboats out of welded poly pipe & sheets-indestructable
The poly pieces & "welding rod" being welded (melted-really) together must be clean,disk sanded rough & of the same material. / Len


Common butt welding

https://www.youtube.com/watch?v=Ic4W5Vk3Hmc

Sheet welding


https://www.kingplastic.com/methods-...lding-plastic/

[Gary S]

Cross-linked polyethylene is not easily welded. Linear polyethylene can be successfully welded.

[thinwater]

[QUOTE=deblen;2937426]I don't know what "breed" of polyethelyne that is used to make red & yellow jerry cans,for gas & diesel-but it must be the same poly as used for common black poly well pipe & has been welded for years by local cage makers..../QUOTE]


No, it is not the same. I am in the oil/gas business and am a piping and tank inspector, among other things.


Gas/fuel tanks are crosslinked polyethyene, not HDPE. They are also either doped or lines during the manufacturing process to reduce permeability. This is not done with the thick walled PE pipe, because it interferes with welding.


What will happen is that the material will appear to weld, but the materials do not actually blend and the result is no more than a glued-on connection, with a fraction of the strength of blended welding. It will seem welded, but it will be several times weaker than the original.


It's just not worth it. Sell the wrong tank and buy the right tank.

[skatun]

[QUOTE=thinwater;2937463]

Originally Posted by deblen

I don't know what "breed" of polyethelyne that is used to make red & yellow jerry cans,for gas & diesel-but it must be the same poly as used for common black poly well pipe & has been welded for years by local cage makers..../QUOTE]




It's just not worth it. Sell the wrong tank and buy the right tank.

Well I can not find a tank that fits perfectly!! And I thought it would be almost perfect to start out with one that its just slightly to long....