Crosslinked Polyethylene repair

[Eric S]

Well through a good deal of time and effort, I did my due diligence and contacted several different tank manufacturers of PEX (crosslinked polyethylene) products, as well as plastic repair outfits, and materials handling companies. It led to two different solutions, and due to the nature of the injury, I narrowed that to the following.

First off, the incident:



Circular saw gouge into PEX tank, approximately 1" - 1.5" deep, approximately 4" - 5" long. The damage was not through and through, but grazed the interior portion of the tank. This resulted in a thin flap on the exterior, a 1/8" thick slit, and a very thin surface wall to the tank side which lightly pulled away. It was not easy to get into the main tank body, but there was room for air to escape.

I contacted the Gougeon Bros about a few of their products for plastics, and they steered me to the G-Flex line. The tech was informed of the problem and sent photos, for which he outlined a simple and thorough procedure to follow. The chemical makeup of the G-Flex allows its use in fuel storage settings like this, with a very minimal change in properties with fuel contact. He recommended the thickened G-Flex, using a flame treatment (key item), then fiberglassing in an oval shape.

First off, PEX is a low surface energy plastic, meaning that it essentially will not stick to anything, and nothing will stick to it. What Gougeon co. discovered is that by using specifically a propane torch, the non-polarized plastic surface, when contacted by the flame, oxidizes into a polarized surface. This allows materials to stick to it in a normal fashion. What was strange to me is that it doesn't require roughing with sandpaper. The following are direct instructions from Gougeon, included in their product packaging.

Flame treat the area:



Do not melt the plastic or deform/discolor it, just flame treating, creating the oxidation.

While the material is cooling, prepare your various items such as mixing supplies and fiberglass:



Next, prep the area for epoxy/repair by cleaning it with the provided alcohol swabs:



The material comes in tubes, so squeeze out the amounts needed on the provided square sheets (not a bad idea for quickfair as well) and mix thoroughly:



Apply as much material as necessary to fill the damaged area, then lay fabric into the epoxy. This was a little difficult through a thickened epoxy, but it did wet out with some coercion:



Clean and treat everything as you would any other layup, getting the fabric down tight and cleaning up excess. Make sure the fabric is properly saturated, without any dry spots:



Here is the final product:





That's what we have now. It holds over 3 lbs of air pressure without leaking, has cured hard but flexible with the tank (will be able to tolerate the shape changes with the tank's known expansion rate of 3%), and is not possible to pull up with hands or tools. In fact I actually tore up a piece of my thumb trying to get the glass to pull off.

I feel very good about this repair, and will keep an eye on the tank to confirm it doesn't fatigue with age. I have no question in my mind that this repair will hold and will serve for the life of the boat without a problem.

E

[goatram]

A good how to post Eric.









As long as it was never had fuel in it; a good repair

[Eric S]

This tank was cut about 3 days after I purchased it. It doesn't even know what fuel is.

E

[goatram]

And You thought about throwing the baby out! I was Just reminding the Arm chair QB's that it was a good repair. Also any other DIYer's that as long as no fuel was EVERY in it or if it had fuel in it; it needed to be purged and sat empty in the Sun flooded with a none flammable gas For ten years Before that it can be attempted with a torch

[Woody]

Well done.

[Etonfish]

Looks good. Now go out and get yourself a couple of saw horses

[Soulakala]

If you did have a tank with fuel the solution is to drain the fuel. Then add at least a half a tank of water followed with dry ice. Use enough dry ice so you can have a reasonable amount of CO2 flow out of open vents. This would make the cut repair flame safe as the tank would not have the atmosphere for combustion. This method is used to decommission fuel tanks at service stations as they typically have a hole cut into the tank with either a saw or a cutting torch. The first time I was involved with this I had the chicken syndrome set in, run, run fast, this guy is nuts and when that flame cuts through the tank it will surely blow. Well it didn't and neither did the other 3 tanks that day, even though they contained about 100 gallons of gas in each of the tanks. It did take a lot of dry ice. I hope this helps but for me I would rather let the repair shop make the repair, but knowing how the repair should be done I can ask the right questions in selecting the best repair shop.

[Dave Smith]

Originally Posted by Eric S

What Gougeon co. discovered is that by using specifically a propane torch, the non-polarized plastic surface, when contacted by the flame, oxidizes into a polarized surface. This allows materials to stick to it in a normal fashion.
E

Not sure if they "discovered" this process as it has been the standard method of making paint and or epoxy stick to PE for decades world-wide.
Nice job on the repair.
DS

[Eric S]

Dave, that has been the preferred technique for polyethylene. They did some testing when the crosslinked stuff exhibited different properties than standard PE, but luckily the PEX reacted similarly.

I'm just giving it as I was told.

E

[Sallysea]

Just a curious thought, will the fiberglass hold up to the E10 fuel if that is what you are using? The problem with E10 gas and boats centered around older boats that had fiberglass fuel tanks. The ethanol would dissolve the resin over time.

[Eric S]

The G-flex is a different formulation, and I talked with the Gougeon tech specialist guy. He states no worries on Ethanol, it shouldn't cause any concern on this type of epoxy. Those tanks that were getting destroyed were a low grade epoxy with different properties, and had fuel in contact with the entire surface for long periods of time.

This tank repair may actually never get in contact with gasoline because of how the damage occurred. Also, it is in the top of the tank, so only when the tank is above 7/8 full will the fuel even be in the area, so I felt comfortable with that.

E