Salt water installation

[Steve_D]

Guys, has anyone done any recent salt water installations? e.g. desalination plants or the like. I'd like to know what sort of pitfalls there are out there. For example, If I mount a distribution board beside a salt water filter, what issues may I find within the board? do copper terminals get salt build up? Any experience in this area would be appreciated.

[Herm]

Any installation near salt water are prone to severe corrosion especially copper, iron and steel. Even in buildings and cabinets because of the salt in the water vapour. All control components must be rated for this type of service.

[OZEE]

I worked at a radio station in the Caribbean for awhile. Salt-water corrosion was a constant issue. To help combat some of those problems, our radio antenna was stainless steel and the guy-wires were fiberglass.

There was a huge water desalination plant on the island. However at the time, I was a radio guy, not controls. When I went to tour the facility, I didn't pay any attention to their control stuff - I was busy being "wowwed" by the desalination process and the size of the facility.

I've also worked in plants where acid vapors was a problem (e.g. water deionization). Those vapors will eat the metal - even copper - out of light fixtures!

Like Herm said, you'll need to make sure every thing is rated for this type of service. Control enclosures and exposed components will need to be rated 4X.

[MASEngr]

(I know this thread's a year old, but I've heard that it's polite to re-use an old thread rather than post a new one.)

I've got a new installation using a AD DL-06. The PLC is going to be outside, BUT inside a Nema 4X case (based on the recommendation in this thread), which in turn will be in a sealed aluminum unit (design spec). The PLC is only going to burn about 5W, but that's enough to potentially go over the 55C operating temperature on a hot day if the sun is beating down on it.

It's going to be near the ocean, so there'a a chance of salt fog, splashes, and rain. Will IP65 (or equivalent) switches be suitable, or will I have to up them to IP67 (or equivalent)? The outdoor ******t temperature will be between -20C and +40C. (Those are record-breaking temperatures for the area). The PLC can run from 0C to +55C. It's a hydraulic ramp lift for transporting disabled sailors on a gangway so they can get to their boats when it's not high tide.

So, my questions are:
1. If I use the cabinets listed above, is that enough protection from the salt air? Do I have to worry about the salty air getting into the cabinet during maintenance, or is that such a small amount that I can neglect it? What about humidity? Will the heater eventually dry out the air in the cabinet enough so that it drops below the 5% minimum, or am I worrying about nothing?

2. Can I use IP65 switches outside, exposed to the elements, near the ocean? There's a jetty with a breakwater, so there's not a huge swell or anything. There's just some chance of salt spray. Going to IP67 is an enourmous jump in price. (For example, the joystick changes from ~$60 to ~$400.) A sales rep from a switch company told me that the Coast Guard uses the IP65 switches all the time, and they keep buying more. (Yes, he sells IP67 switches, too, so it wasn't a matter of him wanting to just sell his products.)

3. For cooling, my choices are basically to put in some passive cooling and hope that the internal temperature doesn't get too high and frap the PLC (the vendor said, "erratic behaviour or fail and replace") or put in a small heat exchanger and not worry about it. Uhh... now that I put it that way, never mind. I'll just put in the heat exchanger so I can spend the sunny day in my basement with an iced tea instead of out on a repair.)

4. I had the same question about heating, but I feel the same about the cooling, except "living room" and "hot chocolate". For the minor cost of a little heater, I can "not worry about it". Problem solved. (Isn't it funny how saying problems aloud makes them solve themselves sometimes?)

5. Is it a good idea to have the PLC control the heater and the cooler, or is it a better idead to run that on a seperate system that shuts off the PLC when the temperature goes beyond the operating temperature?

6. What else should I watch out for? Obviously, the switches will be rated to withstand the elements, and the work is going to require approvals from P.Engs and the safety inspectors, but I want to know what else I'm missing. This is my first PLC work, and I'd like to avoid as many mistakes as I possibly can.

Thank you for reading.

[Lancie1]

Mas,

It appears you are in the tough league now. This is not small potatoes, but the type of environment that requires the best you can get. The problem with using anything the least bit doubtful at this site is that it will come back to haunt you, over and over.

Any amount of salty air or water will be harmful, but what can you do to completely eliminate it in this environment? If you find out a way, there are thousands of navy captains that will thank you for it.

Stainless steel cabinets work well, as do fiberglass enclosures. All enclosures should have gaskets or seals around the openings. All conduit and cable openings should be in the bottom of the cabinets. You may want to provide a drain for the rare case where the cabinet gets water in it from blowing spume. Are you using aluminum conduit also?

I would use the IP67 enclosures, cheap protection in the long run. For how many years use are you designing? If it is +20, then go with the best you can find and hope it is good enough.

I would install heating and cooling with thermostat controls, not connected to the PLC.

I would install a back-up battery power supply (small Uninterruptible Power Supply) in the PLC cabinet, to filter out power surges and allow PLC to ride through short interruptions. It will also help keep from losing the program when there is a power failure.

Write a maintenance manual, make a list of spare parts to keep on hand, and recommend how often the equipment needs inspecting, testing, and painting.

[MASEngr]

Lancie1,

Thanks for the reply.

I can get IP66, but not 67. The problem is that the end users are going to have limited abilities, so I can't have a honkin' strong joystick as the primary control. The best compromise I've found so far is a XD5PA24, which is IP66 and has a 0.14Nm actuation force.

I'm not worried terribly about the enclosure. I'm going to buy a nice, gasketed, waterproof enclosure for the PLC and keep it as dry as I can. I'm fully aware that salt water = instant death for electronics. The control panel cabinets will be done by a shop that's going to slap a CSA rating on the enclosure, and we'll put nothing in there except some more COTS CSA-approved parts.

(As for the trace amount of salt water, like you say, if I can come up with a solution, I'd be a pretty popular fellow. I've thought about filling a clear enclosure with mineral oil so you can see, but not touch, the PLC - and use remote access to program it.)

We are going to have a maintenance schedule developed as well. The operating life of the entire structure is going to be 25 years, but I don't expect any of the electronics to survive nearly that long. I haven't speced out the wire yet, but I was planning on using armoured cable for the exposed parts, and making sure it's aluminium since that's what the rest of the structure is built from. (I've seen how fast that SW battery makes mush out of your dissimilar metals.)

There will be a back-up power supply that will keep the entire system (including the motor) running for at least 2 hours.

Please tell me that the PLC I chose is okay. (DL-06). I couldn't find anything with as much I/O without going into the stratosphere in terms of cost or the ridiculous factor in terms of use.

Ach, no preview as I must leave immediately to pick up the kids.

[Lancie1]

The Automation Direct DL-06 should be able to handle the task.

If this equipment is going to be located on a public dock, don't forget about vandalism, pilfering, and plain old abuse of the equipment.

[MASEngr]

Originally Posted by Lancie1

The Automation Direct DL-06 should be able to handle the task.

If this equipment is going to be located on a public dock, don't forget about vandalism, pilfering, and plain old abuse of the equipment.

Thanks for the vote on the DL06. I'm actually quite enjoying it, and I've found that the DirectSoft programming environment is really nice. (I've paid a lot more for custom compilers that have done a lot less.) Truth be told, I'm a little concerned about how well it's going. I'm sure we've all read the study on "wearing the juice". (If you haven't, here's a link.)

Anyway, the dock is "technically" accessible by the public, but they won't usually get in there. There are people around most of the time, and it's on Federal Land (e.g. part of a base).

Like I said, the PLC is going to be in an enclosure, which in turn will be in another enclosure, inside the moving platform on the ramp. It's going to require tools, directions, and a lot of obstinance to get in there. (So, 5-10 minutes for a meth addict who has to get his next fix.) The exterior structure is marine-grade aluminium. Either way, it's not up to the elec guy (me) how to deal with graffiti. (I suggested electrifiying parts of the superstructure. It was a lot cheaper than all the safety controls. (Which are, of course, completely separate from the PLC.) )

I did bring up the same question about abuse and general stupidity and the answer was "at some point, you have to say 'that's what insurance is for'." The end users will be disabled sailors who are untrained members of the general public, so some folks will have limited dexterity and stamina in terms of button use. Thus, I had to make sure the buttons were big enough to use yet still be sturdy enough to withstand SOME abuse. Futher, the standards we are complying with require that no training is required to use the carriage, and all functions must be obvious to a first-time user.

[phebejtsov]

i've used GRP(glass reinforced plastic)aka. fiberglass type of enclosures.