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In a message dated 8/26/2010 7:54:59 P.M. Eastern Daylight Time,
lanceind@earthlink.net writes:
304 stainless steel is not suitable for saltwater use Dan is right. 304 stainless will rust with prolonged saltwater contact. It
lasts longer than mild steel but still rots out. Especially at weld zones.
If stainless is rinsed well with fresh water after being submerged it helps
a lot.
I don't anticipate leaving my sub in the water for extended periods, and
will be rinsing it after each days dives. A pressure washer will work well for
both inside and outside. Calif. requires all boats to be washed and inspected
before being moved from lake to lake to prevent mussell infestations.
I've considered coating the tank interiors and will run some test
samples with different coatings to see how they perform.
The cost of 316 SS is pretty high and you still need to deal with the weld
zone problem.
Using cover gas or weld paste on the back side of a stainless weld helps
keep the alloy clean, improving it's corrosion resistance. Careful application
of heat during welding is important. You don't want to "cook" the stainless so
that the alloy begins to separate. Cleaning and polishing the welds after
completed helps retain the corrosion resistant properties.
Fiberglass tanks could be a good choice. I went with stainless because I
expect to "crash" into rocks and metal tanks will dent rather than break
open.
With the 304 tanks I have, good surface maintenance both inside and out
should provide a fairly long life span. Experience will tell just how long. The
best choice if you can afford it would be the 316 alloys.
The use of "soft" tanks has some merit. I think the "Triton" subs have soft
tanks that collapse when empty, and are contained within fiberglass tubes. This
probably reduces drag when traveling submerged.
Frank D.
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