Thanks for sharing all these details and for identifying ways to make the penetrators better! This is something we’ve been struggling with for a while now and we’re putting a lot of effort into improving it. What you’re sharing is obviously concerning and this is really important to everyone on our forum so I’m going to make this long and go into some detail on what we’re doing.
We’ve been making penetrators (mostly) the same way for several years now and we’ve had leaks from time to time, but it’s definitely become more prevalent in the last year or so and as our overall volume has increased. When we started seeing more cases last year we made a number of changes in our production to try to improve the situation - we started storing epoxy cartridges differently, adjusted the potting method, changed cable cleaning and preparation steps, and tried surface preparation and anodizing options. We may have made some minor improvements but still kept seeing issues.
It’s really hard to confidently validate what works and what doesn’t work here! It’s a statistical problem generally - say the failure rate is 1% overall and we want to change something to improve that. Since the failure rate is low we need to make tens or hundreds of samples and test them all exhaustively to confidently identify whether the changes make things better or worse! We didn’t have the capacity to do that initially, so most of the changes we made were implementing epoxy best practices that we could be fairly confident with. That didn’t make a big enough impact.
Since the end of 2019, we’ve realized that we need to solve this problem conclusively. We’d like to solve it as quickly as possible, but we’re focused on solving it properly with a long-term solution so that our products can be used with great confidence. We’ve redirected nearly all of our engineering resources to doing that since January. We’ve tested a lot, learned a lot, and made some good progress towards fixing this. It takes a lot of time to make progress on this due to the testing requirements.
From January through March we tested hundreds of penetrator samples in relatively controlled experiments varying things like surface preparation and epoxy cure cycle. These were tested through pressure cycles in our chamber, different amounts of thermal cycling, and physical cable strain. Initially we were having an extremely hard time getting anything to fail at all, even out of large sample sets, but we eventually identified that the epoxy loses a lot of its mechanical strength and adhesion at elevated temperatures. That could happen during shipping, while sitting out in the sun, or even while operating in warm waters (like 80F). Our current data points to this being the primary failure point and we have seen a higher failure rate in warm environments compared to cooler environments.
We have identified a few changes to the process that seem to make a strong positive improvement on this situation. We were about to start a series of tests to validate that before we make those changes in our production, but that was cut short by the COVID-19 crisis and our engineering team is unable to complete that testing until the “Safer from Home” orders end in California.
In the meantime, from home, we’ve still been focused primarily on this issue and we are investigating further options and design changes to fix this issue. We’ve made some promising progress there but we won’t be able to test that much until we’re back at the office, sadly! We hope to have a solution soon after that!
In the meantime, please let us know if you’re having issues and we can make the best recommendation and help you stay in the water. Our support team will be happy to help you with that. We’ve been doing the best to take care of any customers affected by this issue.
- For now I would recommend avoid high temperature exposure when possible and, in particular, avoid putting strain on the cables while they are at high temperatures from sitting in the sun.
- I would also recommend removing the vent plugs when transporting to avoid a combination of pressure build-up and temperature increase that could push outwards on the potting and trigger issues.
I do want to take a moment to address your solution. I don’t know conclusively if it will work better or worse, but I can at least share some things we’ve learned that are relevant to it!
- There’s a good chance that the bare machined aluminum will have better adhesion to the epoxy. You might be able to improve that further with the use of a primer like Reltek A-3 or Forsch Primer.
- I’d be cautious with the grooves inside, they do provide mechanical restraint, but they also create stress concentrations that could trigger delamination of the epoxy. We have seen some correlation between sharp corners and delamination in our testing. (That applies to the sharp corner at the top as well).
We’ve had some recommendations from other customers that you could try to repair these in the meantime. We haven’t tried these ourselves so they are unvalidated at the moment:
- You can backfill the other end of the penetrator to make sure it is full of potting compound
- If the cable has come loose entirely, you can reinstall the penetrator with machining (like you’ve shown) and/or a different potting compound. We’ve heard good things about E-90FL, JB Weld Plastic Welder, 3M DP-420, and 3M DP-620 from various customers.
We realize the importance of solving this issue so that you and other can count on our products! I can assure you that we are doing everything we can to solve this problem and back up that solution with scientific testing and results. We hope to share the results of all of our testing, successful and unsuccessful, when we are done in hopes that others can learn from it.
Thank you again for sharing your concern and your solution.