IMO, any efforts to salvage a leaking metal waste tank is wasted
effort...only briefly delaying the inevitable..'cuz the first leak is
always just the FIRST leak. For the short term, patching a leak with
Marine Tex accomplishes as much as anything else.
My UT's of the tank earlier (now yesterday) fail to
find evidence of generalized deep pitting or widespread wastage (IWO of
what areas may be UT'd in situ), dictating further inspection before
any conclusion may be drawn (even though we'd both expect it to be
quite deteriorated otherwise if it had been used much - it wasn't).
I suspect you'll find a considerable amount of pitting in the bottom of
the tank.
It's also the general order of the day for weld-o-let welds to locally
pit or waste faster in typical tanks & pressure vessels.
As I said before, welds are the first thing to leak because they oxidize
faster than the tank wall.
I'm seeking a coating recommendation involving a product more readily
found around the boating scene, as simply one part of only one option
that is not yet ruled out.
What I'm trying to tell you is, there is no coating that will extend the
life of a metal sewage tank long enough to be worth the effort and expense.
Removing a tank and putting it back, and also often running new piping
to replace hose that has become permeated with odor is 90% of the job.
Since anything you do to the existing tank now will only mean doing it
again in a year or two at most, why do it twice?
The Owner & I have a combined 80 years of responsible ship repair
background, Peggy.
That may be the problem. But I ain't no spring chicken any more either!
The poor quality/durability of the cheap thin-walled plastic tanks
sold by retailers and those used by many production builders to keep
costs down have convinced many an "old salt" that metal is superior to
any plastic tank...and that salvaging what was a good quality metal
waste tank is preferable to replacing it with plastic.
It's true that a rush delivery of a new tank of approximate & workable
dimensions may be possible and that is already concurrently pursued; we
may be old but we ain't dead yet. But I'm not looking for a coating
option for plastic. 8-^) Well, yet. :-)
You wouldn't need one. The purpose of a coating is to protect METAL from
the corrosive properties of urine....plastic doesn't corrode.
In any case I disagree that the old tank, even if found to be beyond
interim repair, should be thrown into a dumpster right after removal.
As related, it has been carefully fabricated for best & fullest fit.
It will be measured & drawn for eventually fabbing a 316L tank at
convenience as the Owner's preferred future installation. Someone did
an outstanding job of fabbing a small tank from the wrong material; we
don't throw away the good part of another's effort with the bad of
their ignorance. Instead, we come up with the best interim fix we can,
and then do the job *really* right.
Then you do not want to use ANY metal..you'll only be repeating the
previous owner's mistake. An uncoated SS tank--even thickwalled 316--has
about the same average lifespan as aluminum...coating the inside of the
tank only extends the life of any metal sewage tank by a few years at
most. Thickwalled (min 3/8", increasing with tank size to support the
weight of the contents) PE is the only recommended materal for sewage
holding...rotomolded preferred...welded acceptable, keeping in mind that
the integrity of a welded plastic tank depends entirely on quality of
the welds.
Btw...you haven't mentioned the size/type of the boat or its intended
use. Most of the people who pop in only a few days before the Memorial
Day or July 4th to ask how to deal with an immediate pressing problem
are only looking for a short-term solution that will allow them to use
the boat for the holiday. A paucity of any information to the contrary
is not conducive to eliciting advice applicable to an individual's
particular needs and circumstances, should such an assumption be erroneous.
But I do have a sense of humor on USENET. :-)
So do I.
--
Peggie
----------
Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://www.seaworthy.com/store/custo...0&cat=6&page=1