Home        Store        Docs        Blog

Big Problem with the Thixotropic Glue

(Jay Abraham) #1

we potted our penetrators this tuesday with the wetlink thixotropic glue and we waited 4 days and one of penetrators with the glue on them seems to be soft. we followed all the instruction but when we were cleaning the jacket of the wire of the t100 thruster, we used isopropyl alcohol instead of acetone. would this have an effect on the curing process. i do want to preface that everything was dried when we potted. We also slightly dabbed the end of the wire jacket with superglue so we could have a secure hold with the wire and the penetrator when we were potting. would using acetone to clean the wires or super glue to hold them in have an effect on the curing process?

#2

The acetone is nice because it’s caustic and etches the surface of the cable, but if you look at the inside of the penetrator, they’re super smooth and the acetone isn’t going to etch it, so my opinion is that cleanliness is the critical element, not so much how you get there. You could probably use hot soapy water and it’d work just as well, as long as it dried out.

The super glue is probably fine, chemically speaking, if it had cured. You really shouldn’t have used it though. Penetrators have three inner diameters; the larger outer one where the epoxy is visible, then next smaller one is meant to grab the jacket of the cable, then the smallest one is a through hole where the wires exit. If you watch the video, you will see that you the superglue is a bad idea because it would prevent you from raising and lowering the cable to get a little bit of the epoxy to flow down into the smallest hole to coat the wires.

They want the epoxy to wrap around the end of the jacket and onto the wires so that if you get a little nick in the tether jacket, water doesn’t migrate into the electronics bottle. You can probably still do it your way if you really wanted to, but it should be a two-step process where you use a syringe to backfill the penetrator from the wire end. In the future, just bolt the penetrator into a cardboard box, but you’ll need some sort of washer because the threads don’t go all the way down. You can get a coat hanger or welding rod or even another cardboard box to use as a support for the cable. then ditch the superglue.

Now, this epoxy isn’t like anything I’ve ever used. It’s super weird, takes forever to cure and isn’t confidence inspiring at all. But! It does seem to eventually cure. Might take a week or more. Did you use a mixing tip and squeeze out the little unmixed bit at the beginning? And what are your temps? Even with several hours at the fast-cure 220 degree heat (or whatever the temp is) it still doesn’t cure very fast and feels mushy for days. It’s a pain to work with, but I haven’t see anything else that cures at 80A (I think that’s what it is). It should be able to handle the temp and pressure cycles better than most anything else. Anyway, keep it warm for a few days, like 80F or better, then let’s see if it improves.

(Jay Abraham) #3

thank you very much corndog for your extentensive and detailed explanation on what not to do during the potting process. in response to your previous question, i did use the mixing tips. i am shocked that the curing process took this long and it is problematic because we are on a tight time schedule and we have to submerge the ROV. we actually had to cut the wire from all of our T200 and T100 thrusters and we had to redo them again. If you’re right, could we benefit from putting the penetrators in a heated environment such as a room with a heater in it. also i just want to make sure, would using isopropyl alcohol on the jacket have any effect on the curring. could there be any residual alcohol on the wire even after it is completely dried. could that small amount affect the curing reaction. is it detrimental to use isopropyl alcohol over acetone. i personally don’t believe there is but i have partners who have this opinion. also could putting a tiny amount of super glue a the very end of the wire jacket affect the curing of the thixotropic glue . just want to clarify that the super glue was hardening at hole of the penetrator that stops the jacket from going through the penetrator. thank you very much again for taking your time to answer my question

#4

No problem and I must add the caveat that I’m new to BROV and their Thixotropic epoxy, though I’ve been around subsea stuff for a long time, but your thoughts mirror my thoughts when first using it and I agree it’s not ideal for time and confidence during a field repair. Normally, downtime is just the time it take you to pull the sub, cut and term, then put it back in the water. It’d be nice if there was a similar method for tether term’s in the field.

But, if you told me you could still poke a fingernail in it after four days at 60F, that doesn’t surprise me at all. The general rule is that the dent from your fingernail should bounce back and if it does, iti should be good to go. It takes a while for it to reach peak hardness, so don’t expect it to be like a fully cured penetrator, because it’s supposed to be usable before that. And you might try that Loctite marine epoxy and see how long it takes to cure. I don’t think it would last as long, but it might actually cure in 24hrs and be better suited for a short term field repair.

Anyway, yes, I do think you’d benefit from putting the penetrators in a heated environment for as long as you’re willing. I also think you should be okay to put them in the water before your natural intuition says it’s okay to put them in the water. I really think alcohol is fine and so is the superglue as long as it was dry. The only gray area to me is if the superglue were still wet and offgassing, but I think you’d get a visual indicator from the Thixotropic epoxy in that it should be nice and glossy/shiny and maybe dull or bubbly if something else were going on.

1 Like
(Jay Abraham) #5

Thank you very much! This was extremely I formative and very helpful!

(Adam) #6

Hi @jjabraham,

@corndog covered everything very well, I would just like to make a few corrections and add some more information.

You can find my response to a similar question regarding air curing time and necessary conditions here:

Our potting guide covers the usage of the Wetlink Thixotropic Epoxy quite thoroughly, and there is one line in particular in the introduction that is relevant to your question:

Proper surface preparation with acetone is required to achieve proper performance.

Unfortunately just cleaning the cable surface with isopropyl alcohol is not sufficient surface preparation in our experience, and will result in the cable jacket peeling away from the epoxy with enough pulling/stress. Acetone is require to chemically attack and alter the surface, resulting in a much stronger bond.

I have no idea how superglue would affect the curing of the epoxy, but we have never tried and do not recommend doing so, primarily for the reason conrndog mentioned:

Moving the cable up and down and around is a critical step to get the epoxy to fully coat and seal the jacket all the way down into the shoulder area of the penetrator (see diagram in potting guide), as well as the cut end of the jacket. In our testing, we found that getting full coverage in this area could make a significant difference in overall performance, especially when stressing/pulling the cable.

@corndog, covering the bare wires is more a side effect of this procedure that shows it has been done properly, rather than the goal. The epoxy here will not stop water from moving past it if the cable jacket is cut, thus it is critical to check for cuts in the cable jacket before a dive. Potting the back entirely will not help with this either, the geometry is not right to keep high pressure water from forcing its way through. It may initially slow it down, but will not stop it. The shape of the penetrator is just as important as the potting compound to seal the jacket, the seal will be solid with an intact cable jacket.

I’m curious, what in particular do you find difficult about using this epoxy? We switched to using this epoxy because of the performance improvements, but also because it is much easier to use. Our production technical have expressed how much easier and faster it is to use rather than the old marine epoxy method. To us at least, it seems like it has the perfect combination of properties to easily flow into place and get everywhere it needs to without much effort, but being thick enough to stay in place and not drip out the bottom of the penetrator during curing. We normally cure for 3 hours at 93°C/200°F, and once out of the oven and cooled off the epoxy is fully cured. Has this not been the case for you?

We spent a lot of time developing and documenting the potting produce in the guide, following the instructions exactly really is necessary to achieve proper penetrator potting performance.

-Adam

#7

Good info Adam. I don’t think I’d tell people that you shouldn’t use alcohol, because it’s one of the best and most common cleaning agents out there that almost all tech’s love, especially over acetone, but maybe the way to look at it is just that using acetone saves you a step of having to scuff the jacket.

As for curing, I don’t have an oven just yet, so I heat my office to 70F or above and let it do its thing. It takes days and I come by and gently poke it every now and again. It stays in a thick gel state for quite a while. Last time I set the heat gun to 220F and let it sit about 6" away for four hours and that worked out to about the same as 24hrs at 70F, so I’m not bothering with the heat gun anymore, but I do intend to try the oven…just need to drive for a day to get it. I just potted some last night, but I don’t think they’re sticking around long enough for me to see when they cure. Some might be and if they are, I’ll try to remember to post when they appear fully cured.

(Nicholas) #8

I had a very similar experience. The issue for me was temperature and humidity as it is very cold and wet at my house this winter. My new process is to put a heat gun on it a few inches away so its ~90C. The heat gun has it set up and movable in about 8 hours. Then I move it to the oven top shelf and use slow cook Lo setting which is ~90C for 24 hours and it’s good to go.