Holding tank over flow vent molded Flange fitting cracked ?

[Capt Robbie]

My plastic holding tank over flow/vent flange fitting is molded into the top of my tank which the hose fittings thread into. I developed a small crack in the molded flange and the tank it's self and I need to repair it.

The flange for the hose connection is not under any pressure because it is essentially just a vent for sewage gasses or overflow if the tank reaches maximum capacity.
Which it never reaches that point.

My question is what would be the best thing to use to seal and reinforce the crack?
In a pinch I mixed up some 5 minute epoxy I had and sealed the crack, now I want to sure it up some how.

I saw that some people have used JB weld on plastic fuel tanks?

I was thinking of trying some west systems resin with thicking agents, then go over it again with some fiberglass. That west systems is some strong stuff. I have repaired lots of things with it but never plastic tank.

Any thoughts would be great!
I really don't want to have to replace this tank for a stupid flange fitting.

 

[Peggie Hall HeadMistress]

Unfortunately there is no sealant that will bond permanently to polyethelyne. If only the female fitting were cracked, it could be replaced...but because tank is cracked too, a new tank is the only permanent solution. (And btw, over-tightening the hose fitting is most likely what cracked the fitting).

Duraweld DURAWELD was (still is?) is the company who supplied most if not all holding tanks to Hunter, so they should be able to supply an identical replacement if you give 'em the boat model, year and size. Their standard wall thickness is only1/4", which isn't thick enough to support the weight of the contents (8.333 lbs/gal) without support on all sides. So although it'll cost a bit more, I strongly recommend that you specify 3/8" wall thickness.
If you don't like Duraweld's price, Ronco Plastics Ronco Plastics marine Tanks may have one that's close enough to fit...they make TOP quality tanks that have at least 3/8" walls for a very reasonable price and they install fittings in the sizes and locations specified by the customer when they make the tank.

--Peggie

 

[JamesG161]

In a pinch I mixed up some 5 minute epoxy I had and sealed the crack

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You can weld Polyethylene. Without pictures I can't tell if you have room to do it. But..
https://plasticstoragetanks.com/poly_tank_repair.htm
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This video has what I would do, which is close cousin to your epoxy repair.

I wouldn't sand the resin, the more resin, the merrier. I would put small patch of matting at the source of the crack and resin on top of the mat. Don't worry about water intrusion from the back side.
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If you want to just reinforce what you did already, add more epoxy but make a layer around the nozzle. Kind of like a "Band" of epoxy following the shape of the nozzle/flange.
Jim...

PS: Blowing off the PE dust is silly, it will help the bonding.
PSS: welding PE

 

[rgranger]

@JamesG161
Very cool video. I did chuckle when the guy got into the tank... thinking about how that might go over with a holding tank.

 

[rgranger]

....I saw that some people have used JB weld on plastic fuel tanks?

JB weld is a 2-part epoxy. I always keep some on my boat in my set of emergency tools and parts. JB also markets a Marine version. I'm betting the only difference is the cost. On the JB website, they say it is suitable for PVC which is not the same thing as PE... but I have used it on PE in the past. Peggie is correct. It is hard to stick things to PE. But there are some things you can do to make it bond more strongly. If you preheat the area with a heat gun (or hair dryer) or use the flat tip of a wood burning tool, you can soften the plastic which then allows the epoxy to "impregnate" the surface a little better. Since a holding tank failure would be a big deal, I would test the bond first using another PE source. Credit cards are also made of PE. Cut your wife's and then see if you can weld it back together... test the strength of the bond by bending the card and see what fails first.

Anecdotally, I once used JB weld to repair a cracked oil pan on a Ford Ranger. I sold the truck 7 years later and the JB was still holding. A quick oil-change company (who I will not mention) had over tightened the nut and cracked the pan right at the threads. We cleaned out the pan with acetone & hexane, let it dry, filled in the old hole with JB and then threaded the JB for a new nut.

I have also used JB to fill in gouges, dings, nicks and the occasional blister on my boats. Fair it with a squeegee and then barrier coat. Always good results.

 

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[thinwater]

Credit cards are PVCA and ABS. Not closely related to PE. The bonding characteristics of these plastics are MUCH different. PE is more closely related to Teflon.

Epoxy will not stick. Heck, we clean our PE mix cups and spreaders by flexing once after the epoxy is cured. Don't waste your time. This includes JB Weld.

Certain polyurethane sealants stick fairly well if the surface is sanded and then flamed (google this). It is NOT to melt the PE, but rather to modify the surface chemistry just a little. Sika 291 and Locktile PL S40 bond well, 3M products do not. It is not a structural repair, but it can make a secure patch, particularly if reinforced with some cloth.

Welding is best. Practice on something else, it is trickier than it looks. It can be permanent.

And Peggy is right. The cause was probably over tightening the fitting.

 

[Peggie Hall HeadMistress]

If it were a water tank I'd try welding it. If it were just the the threaded female collar on a fitting on the top of a waste holding tank that's cracked, I might try welding it. But his crack has already extended into the tank wall and will try very hard to continue its journey, 'cuz even temperature changes will cause the tank to expand and contract. Successful heat welding is learned skill that also requires quite a bit of practice....it's not nearly as easy as filling gouges in snow ski bottoms with P-Tex and a hot clothes iron.
So keeping it mind that it's always cheaper and easier (and likely to be lot less stinky in this case) to do anything right the first time than it is to do it over, I'd replace the tank.
That's my $.02 worth anyway...

--Peggie

 

[Capt Robbie]

Perhaps I was incorrect in my description of my flange crack.
The tank appears to have a welded flange/ nipple fitting that has inside threads. The nipple has a shape that looks like a plastic nut that has inside threads, that a barbed threaded hose adapter can thread into.
The crack is on the nipple fitting which is welded to the tank and protrudes out of the top section of the tank.
The crack is not in the threads but between the nipple and the tank its self. I will try to take a picture the next time I get to the boat.

The crack appears to encompass 1/2 of the nipple and looks like it was caused by me when I changed out all of the hoses two years ago. I probably stressed it trying to pull off the hose.

Again the tank it's self is not cracked just the nipple that is welded to the tank. I am curious to see if the epoxy held. Looked like a pretty good bond when I left. Just look for something that will provide more strength and stiffness.

Like that fiberglass jelly resin James posted.

 

[JamesG161]

the tank it's self is not cracked just the nipple that is welded to the tank

I would not PE weld that. It was the stress on the weld that cracked before.

Industrially we would lay up at least two layers of Fiberglass mat on a nozzle/flange in a tank. This is minor internal pressure.

1) I would prepare the nipple/tank surface like the video. also do what @rgranger said about preheating if you can.
2) Fill the crack or over the epoxy you repaired, like the video. and before it sets...
3) Wrap a Fiberglass Resin soaked/brushed on, mat [on both sides] so that at least a 1/2" of the mat was on the tank and rest of the mat up as high as you could on the nipple. You can pre-cut the mat and even "patch" cut it in pieces, if you over lap the pieces. Kinda like wrapping a sore ankle, a little on the heel [tank] and some on the leg [nipple example]. Don't spare the resin.
4) Let that dry overnight and it shouldn't be tacky to the touch before next layer.
5) Spread new resin, over the dried resined mat.
6) Repeat Step 3.
7) Done...
That will be industrial strength way to reinforce a tank nozzle/nipple.

Jim...

PS: I forgot to add this link.https://www.walmart.com/ip/Bondo-420-Fiberglass-Resin-Repair-Kit-1-2-Pint/17056867

 

[Peggie Hall HeadMistress]

The tank appears to have a welded flange/ nipple fitting that has inside threads. The nipple has a shape that looks like a plastic nut that has inside threads, that a barbed threaded hose adapter can thread into.

Ok...it's obviously time for a little "tank fittings 101" info:
That "nipple" is a female threaded tank fitting. Tank mfrs spinweld (a type of heat welding that requires a special tool and considerable skill) them into PE water and waste tanks. A thread-barb hose fitting is threaded into it...a hose goes onto the hose fitting. Over-tightening the male threaded hose fitting when threading it into the tank fitting is the most likely reason the fitting cracked. Tank fittings are NPT (National Pipe Thread) standard, which is slightly tapered--too slightly to be visible in such a short length of threads. When it comes to holding tanks, people want to make sure the threaded hose fitting can't leak so they crank it down as tight as possible...which is the wrong thing to do because over-tightening the male hose fitting puts stress on that female "collar" that'll cause it to crack...sometimes immediately, sometimes it can take months depending on changes in temperature. But it will happen. So when installing thread-bard hose fittings, tighten it NO MORE THAN ONE turn past hand tight (even less if you're a gorilla) plus enough to aim a 90 in the direction it needs to go.
Warming the end of a hose (I always used a blow dryer) make it a lot easier to remove...warming the hose lubing both the end of the hose and the fitting with a bit of K-Y surgical jelly (much slipperier than dish soap and water soluble so it dries out) makes putting on the barb much easier.

If there are any plastics fabricators in your neck of the woods AND you can get the tank out of the boat AND get it VERY clean and odor free, one of them should be able to spin weld a new fitting into the tank for a very reasonable price.

--Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein

 

[ice breaker]

I agree with most posters that PE is almost not repairable. The option that I might try would be to immediately stop drill the crack then install a clean out port that is sold for fuel tanks, and then tap the vent line into the middle of the new SS cover plate. Short of that, PE seldomes supports any glue/epoxy etc.. GOOD LUCK!!!!!

 

[Peggie Hall HeadMistress]

Only a couple of things wrong with that idea. 1. The crack turns out to be ONLY in the vent FITTINH, not in the tank wall.
2. stainless steel is a good choice on a fuel tank, but a bad choice for a waste holding tank or anything in or on the tank that comes in contact with the waste, which a cover plate most certainly will do--a lot! Urine is so corrosive that it'll corrode a steel cover plate enough to seize it in a year or two....it turns a metal holding tank, even 316 SS, into a colander in an average of about 10 years. However, a plastic inspection port and threaded cap (Beckson is the leading mfr) would be a good idea.

--Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein