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From my related question, I want to know about sea spray being ingested into a piston engine during flight. Will this immediately corrode the engine unless there are special materials?

I'm asking this for piston engines, not jets or turboprops. I'm especially interested in WW2-era planes.

Obviously this is primarily about naval aircraft built for saltwater environments, but I'd like to know the protection measures so I can see if a land-based aircraft can be easily modified, or if it's going to need an entirely new engine.

Note: At very high temperatures, corrosion is much faster. I don't know the math for corrosion, but my worry is that sea spray in the engine could cause some cracks somewhere after just a few flights, unless things are made from a much higher (more expensive) grade of stainless steel or aluminum alloy.

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Seaplanes operate from coastal saltwater all the time, ingesting lots of seawater, and they don't do anything special to the engines to deal with seawater ingestion. The effort is mostly on keeping salt rinsed from the airframe and engine externally and they normally get a fresh water rinse at the end of the flying day. Some operators may spray nicely atomized fresh water into the engine intake while running it to rinse salt from intake passages and carburetors etc, when they are doing the external bits.

The other measure is keeping the protective coatings intact, including the paint on the engine. You really don't want salt on an engine where paint is flaking off aluminum fins or areas of the head, because corrosion pitting results that leads to cylinder head cracks.

So the main protection measure is, keep the salt rinsed off as much as possible with fresh water, and maintain the protective coatings. Even with all that, coastal aircraft operating daily from seawater year-round often require airframe rebuilds to deal with corrosion maybe every 10 years or so.

In any case there aren't any physical modifications you can do to an engine.

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  • $\begingroup$ Well at very high temperatures, corrosion is much faster. I worried that it could cause some cracks somewhere after just a few flights, unless things are made from a much higher (more expensive) grade of stainless steel or aluminum alloy. I shoulda put a note of that in the OP, will do so now. $\endgroup$ – DrZ214 Jul 19 at 22:53
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Corrosion is not something that occurs "immediately". It happens gradually, when a metal is exposed over a long period to an environment that degrades it (such as a salt water environment, indeed).

The parts of an aircraft that are most at risk from its environment are the parts that are exposed to it, and not the internals of its engine.

Inside the cylinders, and other parts of the engine such as a carburettor, the conditions are extreme (high pressure, near vacuum, high and low temperatures, presence of concentrated substances, etc, and rapidly-changing).

A little bit of salty moisture that manages to get in is going to be swept away from those internals pretty swiftly. In the cylinder, the cylinder walls and the piston are also wiped (several times a second) by their own movement.

Inside the engine itself is not really an environment in which corrosion can get started.

That said, salt water generally isn't very good for machinery, and there will probably be other internal parts where salt and moisture could hang around longer and cause a problem, especially where there are two different metals in contact with each other.

The remedy in these cases is not special materials, but maintenance procedures.

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  • $\begingroup$ I meant more like after a few flights. At high temperatures, like in an engine, corrosion is much faster. I put a note of it in the OP. $\endgroup$ – DrZ214 Jul 19 at 22:55
  • $\begingroup$ Corrosion internally is not so much from moisture or salt. The parts are all coated in oil. It's corrosive compounds that build up in the oil itself. Seawater operations might result in trace amounts of sodium in cylinder blow by but it's the acids formed from other combustion products that are the problem. Lycoming cams are particularly susceptible to this, but it requires the engine to sit for very long periods before significant corrosion gets established. For an airplane flying regularly, internal corrosion is simply not an issue, salt water or not. $\endgroup$ – John K Jul 20 at 0:39

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