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Operation of oil submerged boards at high pressure (240 bar)

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emontllo

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Hello,

I have started the design of a project where electronics will be submerged in dielectric oil at high hydrostatic pressure (up to 240 bar). I would like to know if someone has experience in this kind of designs or if you could provide some information like:
- Prefered packages and materials
- Performance degradation of capacitors, resistors, etc.
- Sensitive components
- Typical component fail
- Oil effect on electronics
- Others...

We do have a high pressure testing facility, and I have read some papers on the topic; however knowing previous experiences will be of great help. Thank you!

Ernest
 

BradtheRad

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Certain plastics deteriorate when in contact with oil.

Mil spec components stand up better to harsh conditions.

Relay contacts may not work if oil gets on them. Plastic relay housing will implode as they're submerged, unless given time to fill up with liquid inside.

Vacuum tubes probably will not survive. Nor glass tube fuses, reed switches, mercury switches, etc.

Capacitor housings (thinking of electrolytics particularly) are designed to hold together under pressure from inside. Don't know about pressure from outside.

Same issues with batteries.

Will the circuit be under seawater at any time? Some sea creatures are attracted to electromagnetic fields. Underseas cable operators have had cables bitten by sharks.
 
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emontllo

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Thank you!

I'll check for Mil grade components. Clearly, the components which have voids inside should be avoided. The problem with the oil are some sodium, chloride and heavy metals that are agressive with plastics. We are studying adding a thin resin layer on the PCB and components after mounting.
The circuit will be mounted on a submarine inside a thick stainless steel enclosure, so no problem with sharks :)
 

jiripolivka

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I always wonder how people try to invent quite impossible things like you do.
Electronic components are generally designed for a "standard" environment where also people live. In some cases, temperature extremes are asked for, etc.

If you insist in putting your electronics into high-pressure oil, you would find that some components cannot survive or function. The next question is- can you manufacture such components so they could? And for what cost?

I would start a bit differently. I would try to make sure there are no heat-developing components. If you need to dissipate some reasonable power (say < 1 Watt), provide good aluminum heat sink. Then I would consider molding your electronics in a resin mold, like Epoxy or a similar material. You should test such molding; instead of electronics , make small cavities in the mold block, to see if the mold survives... and if it could protect the innards from a high pressure.

Otherwise, install your electronics in a strong spherical metal enclosure that can stand the pressure and can keep inner pressure in a reasonable level for the electronics. You would need some feedthroughs for wire connections, consider glass beads like in ancient times were used for electronic tobes. As they separated vacuum from an atmospheric pressure, they can do it for your high pressure, too.

You are planning an extreme environment operation, consider an extreme effort to operate your electronics in it.
 
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