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I work in a pharmaceutical plant where saline solution is produced and bottled. The environment has to be clean (by pharma standards), which rules out many greases and other protective coatings. As expected from a saline environment (from my experience it can be as agressive as a marine one), the corrosion over all parts in the room is heavy.

I have mostly controlled the corrosion of structures (all of them have to be made of stainless steel: 316L for those parts in contact with the product, 316 for some others and some structural parts of the equipment are made of 304 SS) by carefully selecting materials, specially material pairs (when I have to), introducing electrical discontinuities in structural joints (if I have a bronze piece, for example, in contact with a SS one, I introduce teflon washers/separators to reduce galvanic corrosion), and at least in one case by using a sacrifice anode.

But the corrosion of electrical components and wiring is something I haven't been able to control, to the point that I've had to replace all the wiring in one of the machines in as little as 5 months. Wires (not only power lines, but also control ones, such as termocouple wiring) get rusted not only in the terminals (where it's evident), but also under their plastic sleeves. In the case of control wiring, this causes noisy signals that result in machine stoppages and downtime (my most recent case is a termocouple that sent a correct signal of 180°C but showed (unreal) peaks of up to 270°C that, of course, triggered an alarm in the PLC).

I can only blame it on corrosion, as the problem goes away by replacing all the wiring and terminals. The wires I took off show corroded under the sleeves, and some of them were brittle. (If you think it's not corrosion, I'd like to hear your opinion).

I can't hide all the wiring from the product (in particular some of the termocouples my get some product spray) and my electrical boxes are as separated from product and tigth as possible (even they don't hold to any IP standard).

So my questions are:

  1. Is there anything I can do to prevent this sort of corrossion in electrical components and wiring?
  2. Is there anything akin to a sacrifice anode that I can use in electrical parts / wiring?
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  • $\begingroup$ It sounds like your wiring is your sacrificial anode. Switch to isolated DC and maintain a DC bias voltage on all wiring. Being small compared to the structure, the wiring is disappearing quickly. You can definitely use blocks of aluminum, magnesium, or zinc to gain control of structural corrosion. These blocks need to be earth grounded. You can also bias the brine if that's easier. I'd get rid of as much metal structure as possible. $\endgroup$ – Phil Sweet Feb 20 '19 at 21:20
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I guess you are using iron/Constantan thermocouples for the relatively low temperatures; so iron is going to corrode badly . Can you change to chromel / alumel couples ? It would require some instrumentation change as they have lower emf voltage. Chromel / alumel is a very common corrosion resistant pair generally used for higher temperatures, but I do remember using them for ambient temperature measurements. Of course an anode connected to a thermocouple would defeat the purpose of the couple. Possibly a coating like a liquid epoxy that the thermocouples could be coated with after they are installed. Can non contact infra-red temperature sensors be used ?

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  • $\begingroup$ Great advice about chromel/alumel thermocouples, thanks. I don't think I can use any coating, as the risk of product contamination is not worth any donwtime reduction. As for using IR, I'll try to explore that option. The thermocouples produce readings of the sealing blocks (it's a sachet packaging machine), so I'll check if the accuracy of IR is enough to control the machine and avoid packaging melting / burning. $\endgroup$ – PavoDive Feb 14 '19 at 1:50
  • $\begingroup$ Have you had any experience with thermocouples type N, T or E? I've read their alloys are used in corrosive environments and their temperature range works for my application, but I'd like to anticipate any potential downside of using them. $\endgroup$ – PavoDive Feb 15 '19 at 10:40
  • $\begingroup$ Wikipedia lists the couples with those letters ; I have already forgotten which was witch . Other than iron and copper all the other alloys look like they have good corrosion resistance. So it would be a matter of comparability with your instrumentation and availability. $\endgroup$ – blacksmith37 Feb 17 '19 at 21:03
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can you reduce the humidity of your production environment? If moisture can be reduced, the corrosion rates can in general be minimized.

Furthermore, there are commercially available corrosion inhibitors which you can spray onto the stripped ends of your wires, which will seep into them and shut off access to oxygen and moisture- and thereby shut down the major corrosion mechanisms you are faced with.

The classic one is WD-40 spray, but in the aerospace industry there are others that are used to corrosion-proof the insides of aircraft; you can probably find references to these on the web.

there are also aerosol lacquers which are used to corrosion-proof electronic assemblies that are used in humid tropical environments; these were first developed during WWII and are still in use today.

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    $\begingroup$ The question specifically asked about pharmaceutical clean room so WD-40 is not a good idea nor the aerosol lacquer $\endgroup$ – workoverflow Feb 14 '19 at 6:13
  • $\begingroup$ Clean room environments are very stringent regarding the use of substances that can be considered staples somewhere else, like spray lubricants, so using WD40 or something similar is not really an option. Keeping humidity low is a true challenge, as the room itself has to be cleaned (that's almost washed!) regularly, and because some product spilling is hard to control too. $\endgroup$ – PavoDive Feb 14 '19 at 10:42
  • $\begingroup$ the OP has a significant problem, then. But given the amount of wiring and signal lines in a conventional clean room, there must be a commercially-available solution. $\endgroup$ – niels nielsen Feb 14 '19 at 18:42
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Conformal Coatings are your Friend!
I suggest you look into "conformal coatings" used to protect electrical and/or electronic components from corrosion. These coatings are commonly used on Naval electronics -- especially for gear used aboard submarines. Use as directed (well ventillated, away from potential spark/ignition sources until fully dry, etc.) on pretty much everything except electrical contacts and moving parts.

So long as you have different metals in contact, you've gotta keep moisture away or else you'll get electro-chemical corrosion (AKA ad-hoc battery.) FYI, such coatings do a pretty good job, but they make probing circuitry harder. I've had to grind sharp points on a set of DVM leads to pierce these coatings; they dry pretty tough, by design.

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