Frigoboat compressors rusting and lines corroding.

[hellosailor]

What WD40 will do is displace water and leave a film of ~kerosene on things for a while. That will just have to be cleaned off before the rusty areas can be repainted with something better, like a cold zinc primer coat.

Better to stop by an auto store and buy a can of contact cleaner, or brake clear, and then first remove the rust and failing, then spray everything down to clean it, and apply new durable protection (primer or zinc paint) over it.

If the controller board is not protected, it probably will benefit from a spray of "conformal coating" designed to protect electronics from moisture.

There are plenty of products like BoeShield that will work if you just need to spray metal parts to prevent surface corrosion from time to time.

[Richard Kollmann]

Originally Posted by hellosailor

What WD40 will do is displace water and leave a film of ~kerosene on things for a while. That will just have to be cleaned off before the rusty areas can be repainted with something better, like a cold zinc primer coat.

Better to stop by an auto store and buy a can of contact cleaner, or brake clear, and then first remove the rust and failing, then spray everything down to clean it, and apply new durable protection (primer or zinc paint) over it.

If the controller board is not protected, it probably will benefit from a spray of "conformal coating" designed to protect electronics from moisture.

There are plenty of products like BoeShield that will work if you just need to spray metal parts to prevent surface corrosion from time to time.

I would strongly recommend against using a conformal coating spray inside this Danfoss electronic already protected module.

[billgewater]

Yes. As a generalization, galvanic corrosion is isolated to the place where the action is. Usually requiring two dissimilar metals and an electrolyte (e.g. salt water, acid etc.). It can be accelerated or reduced by the deliberate or accidental application of an external voltage.
Looking at your compressor body it does not seem to meet these criteria and is simply rusting away due to the presence of (most likely) some salt water dispersed spray. The surface rusting on the large terminal screws also suggests the same issue elsewhere. This type of "corrosion" is generally called oxidation and it differs in rate for different metals and alloys. For iron (Fe) the red oxide formed requires an electrolyte and oxygen and the rust formed actually lifts off the surface exposing lower metal to this oxidation process. It is easy to stop. Remove the electrolyte. Remove (or convert to something safer e.g. iron phosphate) any rust left behind and stop the ingress of oxygen (oil or a good oxygen barrier paint.)
So the problem is most likely not electrical in nature and a good clean up with fresh water (to remove any salt), then a proprietary anti rust paint process is the way to go. Spraying with a fine oil such as WD 40 will certainly help but it won't fix the cause of the problem.
I would spend time and effort to track down where the spray came from as it will ultimately affect other items. Look around carefully at the corrosion pattern and try to see if the spray may have come from any specific direction. Use the wet finger taste on other parts to see if they taste salty as well. If you can taste any salt on say, a rubber hose or plastic surface then you definitely have a salt spray issue.
Another clue may be in front of you. During use, the compressor body and the discharge line get very hot. Higher temperatures usually accelerate surface corrosion so try making comparisons with similar metals that remain cooler during use.

[cardude]

Thanks. I’m pretty mystified by this corrosion from the invisible salt spray. I will do the wet finger test for salt next.

[thethomas]

Hydrogen outgassing from charging wet-cell batteries is very corrosive. If there is bad ventilation in that space which you’ve said contains mechanical components and batteries, you’d see corrosion.

[cardude]

My batteries are AGM and sealed, so I don’t think they do any outgassing.

[Capt Gill]

Originally Posted by cardude
"I did have a raw water pump on the generator dripping last year that took me awhile to catch. Maybe it’s possible that seawater atomized somehow and saturated the air in this area? This area is not sealed from the exterior of the boat either because the generator has to get air, so maybe it is just regular old rust that I didn’t catch. That’s embarrassing"

Just a thought: Given the seawater leak earlier; the water may be gone/evaporated, however the salt crystals remain and act as a desiccant, attracting ambient moisture, so be sure to wash up the area with fresh water if you haven't already.

[cardude]

Will do. Thanks.