Bringing Wire into a Pressure Vessel -- How to Properly Seal?

[CocytusME]

Hey guys,

I'm trying to bring a coaxial cable into a pressure vessel, through a wall or fitting, and I'm trying to figure out an off-the-shelf way to make the seal. I needs to hold 150psi.

A Swagelok would work in theory, but the cable isn't a standard dimension. It's a little under 7/16" thick. How can I handle this?

Regards,
Grant

 

[SnTMan]

Try this:

http://www.conaxtechnologies.com/sg_intro.shtml

Regards,

Mike

 

[pennpiper]

CocytusME,
Just a few questions.
- What is the commodity in this vessel?
- What is the maximum operating temperature for this vessel?
- What does the cable connect to inside the vessel?
- Why are you doing this?

Sometimes its possible to do all the right things and still get bad results

 

[CocytusME]

Thank you SnTMan, I'll read this.

Pennpiper,
It's crude oil and the maximum operating temperature is 90degC. It's connecting to a bus bar.

Thanks in advance.
Grant

 

[moltenmetal]

DO NOT bring the cable itself through the wall through any kind of gland, as the cable's materials are unlikely to survive the combination of temperature and pressure and exposure to solvents it will be exposed to.

Buy a pass-through pressure fitting intended for this purpose. Do such exist for coax connections? I don't know, but Conax is a good place to look.

 

[CocytusME]

A lot of these are perfect for what I described, so in that sense we've figured it out. Thank you.

Unfortunately, I forgot to mention that I'm wiring 70kV into the vessel via that cable. Everything from Conax is 8kV or less.

This is why I thought it'd be best to pass the cable itself through the vessel since it is pre-insulated for the voltage. Don't worry about the cable corroding, it won't.

Thanks for the continued support, btw.
Hopefully we can figure this out.


Regards,
CocytusME

 

[moltenmetal]

Coax cable generally has polyethylene insulation between the inner core and shield, which has near zero strength at 90 C. So good luck getting it to resist the combination of temperature and pressure, especially in the presence of crude oil which contains lots of constituents that can swell and soften plastics especially at elevated temperature. Getting 70 kV into that pot is one thing, and keeping the contents IN the pot is quite another.

 

[Compositepro]

Your application is very similar to the requirements for the bushings which bring wires out of high voltage power transformers or vacuum breakers. AT 70 Kv there are special requirements just for terminating the cable so that the electric field between the core wire and shield doesn't concentrate enough to punch through the insulation. Your question should be posted in the electric power and transmission forum. Better yet, you should have a qualified electrical engineer working on this design. Just the fact that you did not think to mention the 70 kV is a concern.

 

[CocytusME]

Thanks for the info regarding the degradation of PE at temp. That was critical.

 

[moltenmetal]

The 70 kV may short out. Presumably the vessel would be grounded/bonded, and whatever is supplying the 70 kV would also be short circuit protected.

If the cable BLOWS OUT, 150 psig will be propelling 90 C scalding crude oil out of an open hole.

My bet is that the latter represents a far greater risk of injury than the former.

 

[Duwe6]

Might try calling a Code vessel shop that fabs Desalter vessels. They have to bring large amperages & voltages inside the Desalter drum, for the crude separation.