Corrosion can occur and be accelerated under a variety of conditions. Moisture and oxygen are the basic ingredients, and then many other conditions will increase the rate of corrosion. Examples of conditions that generally speed up corrosion are elevated temperatures, high concentrations of oxygen, salt solutions, low pH (acidic), and elevated fluid velocity. Contact with dissimilar metals may cause galvanic corrosion.
Pitting is just localized rust/corrosion; water collects in pits that may form (for any of a number of reasons) and accelerates the rust in the pit. (If there is a lot of water, carbon steel will tend to rust over a
broad area as fast as pits can form so one might not see pits). To put it differently, galvanic corrosion is not the only way to get pitting. And some materials are more prone to pitting than others. And some fluids, like sea water, are more likely to aggravate pitting than other fluids.
(Corrosion is a science in and of itself and people make careers out of it.)
Glass is largely silicon dioxide and is an
insulator and a non-metal. As a non-metal, it does not corrode. And as an
insulator, it could in theory be used between two dissimilar metals to prevent galvanic corrosion.
I would agree that lumber under "normal" conditions would have little affect one way or the other on corrosion, because it is a non-metal and an
insulator. (Although something driven into wood is protected to some degree from the exposure to water and air.) Since bare wood can absorb water, metal in contact with it may stay wet longer and therefore will rust more. (On the other
hand, wood that wet may rot through anyway…)
Not being familiar with the interior parts of a
Leko, I'm speculating; rust in there may be aggravated by the high temperature. I'm assuming that moisture would come from the air, but I never gave any thought as to whether the air high in a room can be periodically moister that the air below. Or maybe lousy, damp storage conditions. Or maybe it’s a temperature change heating-cooling cycle issue, but that seems to be a reach, then again, every location will have specific circumstances…Also, it takes only a short time for rust to form a very thin, but visible layer. Rust-promoting conditions may only occur sporadically and all one may see over a long time is a very thin (and inconsequential) coating of rust.
[It occurred to me that I may have misinterpreted what ship meant by "spread of rust". I've been interpreting it as the spread of the
action of corrosion. On the other
hand, the
iron oxides are weak, porous, and very, slightly soluble, so the
products of corrosion that literally spread over a wider area are nothing more than staining. This is (in most cases) just a nuisance.]
Joe
