My immediate thought is that upside down shouldn't make any difference,
however upon reflecting a bit I can see ways that could make a difference.
Does being upside down cause any part to collect moisture more. In other
words, does it form a recepticle rather than being self draining in the
other orientation.
Look at the rust and see if it is on what is now the lower part (as opposed
to being raised in the upright position).
As far as the seatpost, in the upright position I'd normally expect the
corrosion (under these conditions) mostly near where the seatpost goes into
the frame rather than into the seat. Being upside down, I'd expect the
opposite (as in your experience) as gravity now pushes the salt water
towards the seat. That being said, the problem may be dissimular metals
causing galvanic corrosion (such as steel to aluminum). If the frame and
seat post are aluminum, there should be little electrical current and
therefore little corrosion.
If the metals are close to each other on the series, there is little
galvanic corrosion, but if metals are far apart there can be lots of
corrosion. However sea water has lots of these elements in it so in your
environment almost anything can happen.
All that being said, I like the other gentleman's idea of bagging the bike
with dessicant. I might suggest washing the bike and thoroughly drying it
before bagging it. Please see below for information regarding the
electromotive (galvanic) series.
-Pete
= = = = = =
This is from Corrosion Doctors
http://www.corrosion-doctors.org/
Galvanic Series
Galvanic series relationships are useful as a guide for selecting metals to
be joined, will help the selection of metals having minimal tendency to
interact galvanically, or will indicate the need or degree of protection to
be applied to lessen the expected potential interactions. In general, the
further apart the materials are in the galvanic series, the higher the risk
of galvanic corrosion, which should be prevented by design. Conversely, the
farther one metal is from another, the greater the corrosion will be.
However, the series does not provide any information on the rate of galvanic
corrosion and thus serves as a basic qualitative guide only.
Once you have finished reading the material on this page you can check your
skills with a self test.
Non-uniform conditions along the surface of a metal can also cause different
energy potentials. For example, the portion of an anchor embedded in
concrete typically has lower energy potential than the portion exposed to
soil. The use of the galvanic series has to be done with caution and a basic
knowledge of the environments that is a necessary part of this serious form
of corrosion. The following documents provide different points of view
regarding the ranking of metals and coatings in practical schemes for
preventing galvanic corrosion.
Galvanic Table
The following galvanic table lists metals in the order of their relative
activity in seawater environment. The list begins with the more active
(anodic) metal and proceeds down the to the least active (cathodic) metal of
the galvanic series. A "galvanic series" applies to a particular electrolyte
solution, hence for each specific solution which is expected to be
encountered for actual use, a different order or series will ensue. In a
galvanic couple, the metal higher in the series (or the smaller) represents
the anode, and will corrode preferentially in the environment. Listed below
is the latest galvanic table from MIL-STD-889 where the materials have been
numbered for discussion of characteristics. However, for any combination of
dissimilar metals, the metal with the lower number will act as an anode and
will corrode preferentially. The table is the galvanic series of metals in
sea water from Army Missile Command Report RS-TR-67-11, "Practical Galvanic
Series." (reference)
Active (Anodic)
1.. Magnesium
2.. Mg alloy AZ-31B
3.. Mg alloy HK-31A
4.. Zinc (hot-dip, die cast, or plated)
5.. Beryllium (hot pressed)
6.. Al 7072 clad on 7075
7.. Al 2014-T3
8.. Al 1160-H14
9.. Al 7079-T6
10.. Cadmium (plated)
11.. Uranium
12.. Al 218 (die cast)
13.. Al 5052-0
14.. Al 5052-H12
15.. Al 5456-0, H353
16.. Al 5052-H32
17.. Al 1100-0
18.. Al 3003-H25
19.. Al 6061-T6
20.. Al A360 (die cast)
21.. Al 7075-T6
22.. Al 6061-0
23.. Indium
24.. Al 2014-0
25.. Al 2024-T4
26.. Al 5052-H16
27.. Tin (plated)
28.. Stainless steel 430 (active)
29.. Lead
30.. Steel 1010
31.. Iron (cast)
32.. Stainless steel 410 (active)
33.. Copper (plated, cast, or wrought)
34.. Nickel (plated)
35.. Chromium (Plated)
36.. Tantalum
37.. AM350 (active)
38.. Stainless steel 310 (active)
39.. Stainless steel 301 (active)
40.. Stainless steel 304 (active)
41.. Stainless steel 430 (active)
42.. Stainless steel 410 (active)
43.. Stainless steel 17-7PH (active)
44.. Tungsten
45.. Niobium (columbium) 1% Zr
46.. Brass, Yellow, 268
47.. Uranium 8% Mo
48.. Brass, Naval, 464
49.. Yellow Brass
50.. Muntz Metal 280
51.. Brass (plated)
52.. Nickel-silver (18% Ni)
53.. Stainless steel 316L (active)
54.. Bronze 220
55.. Copper 110
56.. Red Brass
57.. Stainless steel 347 (active)
58.. Molybdenum, Commercial pure
59.. Copper-nickel 715
60.. Admiralty brass
61.. Stainless steel 202 (active)
62.. Bronze, Phosphor 534 (B-1)
63.. Monel 400
64.. Stainless steel 201 (active)
65.. Carpenter 20 (active)
66.. Stainless steel 321 (active)
67.. Stainless steel 316 (active)
68.. Stainless steel 309 (active)
69.. Stainless steel 17-7PH (passive)
70.. Silicone Bronze 655
71.. Stainless steel 304 (passive)
72.. Stainless steel 301 (passive)
73.. Stainless steel 321 (passive)
74.. Stainless steel 201 (passive)
75.. Stainless steel 286 (passive)
76.. Stainless steel 316L (passive)
77.. AM355 (active)
78.. Stainless steel 202 (passive)
79.. Carpenter 20 (passive)
80.. AM355 (passive)
81.. A286 (passive)
82.. Titanium 5A1, 2.5 Sn
83.. Titanium 13V, 11Cr, 3Al (annealed)
84.. Titanium 6Al, 4V (solution treated and aged)
85.. Titanium 6Al, 4V (anneal)
86.. Titanium 8Mn
87.. Titanium 13V, 11Cr 3Al (solution heat treated and aged)
88.. Titanium 75A
89.. AM350 (passive)
90.. Silver
91.. Gold
92.. Graphite
End - Noble (Less Active, Cathodic)
--------------------------------------------------------------------------------
Galvanic Compatibility
Often when design requires that dissimilar metals come in contact, the
galvanic compatibility is managed by finishes and plating. The finishing and
plating selected facilitate the dissimilar materials being in contact and
protect the base materials from corrosion.(reference)
a.. For harsh environments, such as outdoors, high humidity, and salt
environments fall into this category. Typically there should be not more
than 0.15 V difference in the "Anodic Index". For example; gold - silver
would have a difference of 0.15V being acceptable.
b.. For normal environments, such as storage in warehouses or
non-temperature and humidity controlled environments. Typically there should
not be more than 0.25 V difference in the "Anodic Index".
c.. For controlled environments, such that are temperature and humidity
controlled, 0.50 V can be tolerated. Caution should be maintained when
deciding for this application as humidity and temperature do vary from
regions.
<
[email protected]> wrote in message
news:
[email protected]...
> Hi,
>
> I hang my bikes upside-down on some hooks in my shed. I wonder if
> hanging upside-down has contributed to my corrosion problems.
>
> I live by the sea, so the air is salty, and it rains a bit so my bikes
> are often wet. After taking the bikes down from a winter of hanging,
> both my road bike and MTB needed new headsets (SIS steering sucks), and
> the shift cables were badly rusted particularly in the small casing at
> the rear derailleur. And the seatposts had corrosion near the top where
> the head was attached to the shaft that was suspucious enough for me to
> change them. (Broken seat post is bad)
>
> Does anyone think hanging upside-down made any difference? Or would
> these things have been just as bad were the bikes upright?
>
> Joseph
>
