Thread: Welding HDPE issue

We used to use Dow Corning RTV 732 in the healthcare manufacturing industry when I worked for Baxter Healthcare... so very safe!

My experience is in situations like campers nothing really seals HDPE and water will eventually wick it's way under silicone seals.
Still it should last a while - and then you have to remove and reapply it.

You also might want to look at this flame treatment method of increasing surface adhesion.
https://theepoxyexperts.com/flame-tr...esive-bonding/

There are even better surface preparation methods using electric discharges but they are unlikely to be in the DIY category.

I am watching this thread VERY closely! I have several jobs I want to do in HDPE, including new water tanks for my boat. I have researched plastic welding but its really hard to find good information, and its kinda nice hearing your problems so I can go research some more about it. I am really keen to see how you get on, surely its possible to deal with the corner issues and pinholes given you can buy welded tanks exactly like this.

Originally Posted by Pearo

I am watching this thread VERY closely! I have several jobs I want to do in HDPE, including new water tanks for my boat. I have researched plastic welding but its really hard to find good information, and its kinda nice hearing your problems so I can go research some more about it. I am really keen to see how you get on, surely its possible to deal with the corner issues and pinholes given you can buy welded tanks exactly like this.

Some commercially welded tanks are often done by machines

Once trick to get reliable 3 sided corners is to not cut and weld up panels so that the 4 of the 3 sided corners can only be welded on the outside.
Lets say you are welding up a 6 sided tank or box.
Make the box up in two halves, split down the middle and strengthen and leak proof all 8 of the 3 sided corners by welding in triangular patches onto the insides of the corners.
Then weld the two halves of the box together.
The seam can be further strengthened by bending and welding a 50 mm wide strap over the outside of the seam.

Originally Posted by BobL

My experience is in situations like campers nothing really seals HDPE and water will eventually wick it's way under silicone seals.
Still it should last a while - and then you have to remove and reapply it.

You also might want to look at this flame treatment method of increasing surface adhesion.
https://theepoxyexperts.com/flame-tr...esive-bonding/

There are even better surface preparation methods using electric discharges but they are unlikely to be in the DIY category.

Thanks Bob, ill have to look at that, as nothing really sticks to HDPE

Originally Posted by Pearo

I am watching this thread VERY closely! I have several jobs I want to do in HDPE, including new water tanks for my boat. I have researched plastic welding but its really hard to find good information, and its kinda nice hearing your problems so I can go research some more about it. I am really keen to see how you get on, surely its possible to deal with the corner issues and pinholes given you can buy welded tanks exactly like this.

Its a pain to work with Pearo

if it wasn't for the $1600 quote i got for getting one made up, i would have outsourced it.

I couldn't really find much good info on plastic welding, but i can weld steel, so i thought id giver it a go.

I might head up to Altas tanks up the coast and see if they can fix it before i try silicone or expoy.

If i recall, you are around me on the bris northside, your more than welcome to some scraps to practice with.

Hi Bryn,
A few years ago we damaged a tank on our caravan on a trip to Uluru via the Great Central Road. A rock had flung up and knocked the outlet pipe off. When we got to Alice Springs I bought some water resistant Araldite thinking I would do a temporary repair and replace the tank when we got home. There are two outlet ports on the bottom of the tank so I changed the outlet to the one previously bunged and moved the bung to the damaged outlet. After cleaning the threads I mixed up the Araldite and put it on both surfaces and screwed the bung back in. I then plastered Araldite all over the bung and around the join. It's still there and I haven't bothered replacing the tank. I've just googled Water Resistant Araldite and can't find it listed. It's a cream colour. If they've taken it off the market this story won't be much use to you.
Cheers,
Geoff.

Thanks Geoff,

I know that Selleys do a aqua knead, which is an food safe expoy which might do the trick from the inside.

I got back a quote this morning for a 1.6mm SS tank that same as the one i built, but it was $1850, but then again the HPDE quote of $1600 was a sign that it wasn't going to be cheap

So im going to try and fix this first, i've ordered in some bigger 6 inch access ports so i can get better access to the internal welds

Araidite is available.

Araldite® Adhesives - Build, Bond, Protect

If you can't get it there we can work something out and I'll ship it as a Birthday present to my brother.

Originally Posted by rrich

Araidite is available.

Araldite® Adhesives - Build, Bond, Protect

If you can't get it there we can work something out and I'll ship it as a Birthday present to my brother.

Cheers Rich,

Thanks for the offer.

We have Araldite here, i got some in the shed, although i'm not sure its certified food safe.

I've put it on the back burner until i get the bigger access ports next week, so i can open up the tank and see what i can do to solve the issue.

Well i got the bigger ports in, cut them out to see if i could fix the internal welds.

i tried, but didn't have the space to get in there with the hot air welder.

So i tried Selleys Aqua food safe Expoy, although i does say that is isn't Suitable for Poly once you open it up, the instructions are inside.

but i had it, so i tried that on the internal weld pinholes and then Sika 291 marine on the outside and let it cure

Didn't work, although i didn't really expect it to.

So ill just have to get a SS one welded up, should have done this first go, but i was tempted to try my hand at welding HDPE.

Originally Posted by bryn23

So i tried Selleys Aqua food safe Expoy, although i does say that is isn't Suitable for Poly once you open it up, the instructions are inside.

but i had it, so i tried that on the internal weld pinholes and then Sika 291 marine on the outside and let it cure

Didn't work, although i didn't really expect it to. .

Did you try flame treating the seams first?

Not internally with a gas torch, as i decided not to use a gas torch in such an enclosed area, as my face was up against the opening just trying to see where to add extra welds.

I did manage to get a far bit of heat on the seams internally from the hot air welder, but it most likely wouldn't have had the same effect.

I deemed my face and life more important than operating the gas torch inside that tank.