Stratergies for treating rust in our Keel

[ribbony]

Soon we will slip our vessel and one challenge facing us is what process to use for treating the inside of our keel.

First some background. The keel is 5mm plate and contains steel ballast set in concrete or cement mortar, it is capped with a 1/8" layer of epoxy or epoxy paints. However there is a cavity at the stern end of the keel (capped in steel) where a tank was once used for what seems like fuel (diesel). Inserted into this tank was a sump made out of 1/8" steel and that was totally sealed from the tank until a rust hole developed and the tank was no longer used as water must have entered the tank. It looks like that was a long time ago as the other tankage for diesel is far from new. So the keel has had sump water and all it's nice greasy mixtures residing in it for a decade or so.

I drilled some holes in the keel plating to see if there was rust and seemed to get the full 5mm thickness. there is a hairline gap between the plate and contents as water does dribble out of the holes. So we need to stop the problems and treat it for the future.

I was thinking of drilling some holes at the bottom of the keel the next time on the slips and flushing the keel out with fresh water (should I use some degreaser ?). Run this through for a couple of days, then insert a new sump pan welded in and totally sealed apart from a threaded and capped flange that I can use to pour in future treatments. I was wondering if filling the keel with oil or other preservatives would be appropiate.

Would some Fertan (tanic acid based rust converter) added to the final flushings help ?

Cheers

Mick

[Boracay]

I'm new at this rust prevention/control business too.
One point that my surveyor made was that one should never permit water to sit against steel. He was right. Everwhere in the boat where water has sat against steel bad rust has occurred. I am currently drilling drain holes to make sure that this does not happen.
I get the impression that for rust to occur oxygen and a transfer medium (normally stagnant water) is needed.
Normally one puts a good layer of quality paint on the steel and thats that, however this does not seem to provide the necessary protection.
Another poster recomended dusty (totally dry) bilges and this is what I am aiming for.
It sounds like you already have a system that provides some protection. I have noticed that very thick epoxy will actually pull away from the steel, water gets into the resultant crack, the large surface area provides an oxygen rich environment and the steel rusts badly.
I would imagine that you need some way of keeping all oxygen from getting into your keel. Possibly welding a steel plate across the top of your keel and filling any cavities with an appropriate oil.
Long term, if you have the facilities and the money it would possibly be best to cut the keel open, remove the ballast and replace it with lead.
I am using a water blaster to remove all traces of oil from the lower part of my boat.
I have used kitty litter and oil absobent pads to take up the oil. It does take some time to float to the surface after being washed off.
Any oil residue that I cannot take up with the oil absorbent pads I put with the kitty litter.
Using degreasers makes the problem worse as the oil absorbent pads do not work properly.
The whole process has been a pain in the a## as the residue can be expensive and time consuming to dispose of properly.
After oil removal I am wire brushing and repainting.
Where I cannot prevent water from sitting against the steel I am experimenting with using silicon rubber on top of a paint layer as a sealant. However this is experimental and insufficient time has elapsed to permit proper evaluation.

[Alan Wheeler]

I will answer a few of Chris's comments and that hopefully will provide answers to both.

I get the impression that for rust to occur oxygen and a transfer medium (normally stagnant water) is needed.

Actually the oxygen is in the water. Especially fresh water requires oxygen within it to create rust. Rust on steel is Iron Oxide. Stagnant water is usally a term given to water that is totaly oxygen depleted. Interestingly Steel will not rust in oxygen depleted fresh water. Salt water is a whole different process. Although oxygen depleted salt water also does not cause steel to "rust", it can corrode in a different manner. The biggest enemy to steel is when you have steel that is wet then dried then wet then dried, much like the bilge area is subjected to. This allows oxygen from the air to work on the damp steel, plus if the water is stired up in anyway, it can disolve oxygen into it. The air having the most oxygen is the biggest cause of corrosion.

I would imagine that you need some way of keeping all oxygen from getting into your keel. Possibly welding a steel plate across the top of your keel and filling any cavities with an appropriate oil.

this is indeed a very good way of preventing issues. I suggest you use a non petroleum based oil. If you ever do spring a leak, the last thing you want is is petroleum oil leaking into the water around you. A very good oil to use for controlling corrosion is "fish Oil". No it doesn't smell like fish. Cooking oils could also be a good consideration.

Long term, if you have the facilities and the money it would possibly be best to cut the keel open, remove the ballast and replace it with lead.

I am no expert in this area, but from what little I do know, you need to get some proffesional advice on doing that. The Lead will be placing a different weight in a different position changing the boats motion.

The whole process has been a pain in the a## as the residue can be expensive and time consuming to dispose of properly.

Try using the microbial oil solutions. These little critters literaly eat the oil.
Plus, oil in concrete is vertually impossible to get out. It will leach slowly over time and I swear, you get more out than you ever thought could have gone in.

After oil removal I am wire brushing and repainting.

Be very carful of this. It most likely will not remove enough rust to be long term effective. The rust MUST be neutralised before painting. You can use Phosporic acid, then the paint, or the product I especially like is Plast-kotes product. Can't remember the name but it is white and then turns black on the steel. Then you paint over it. Or you can use etch primers which work well but you MUST follow the instructions for a good result. PA10 is a primer with 10% Phosphoric acid in it. There is a new product here I have seen advertised, but never tried called POR15. If it lives up to the claims they make, it could be a great product.
Wire brushing is almost never good enough for coating preperations. The only really effective way to prepare steel is to Sandblast it and have it primed within a specified time.

. Where I cannot prevent water from sitting against the steel I am experimenting with using silicon rubber on top of a paint layer as a sealant.

Interesting thought. It may work. But do ensure you use a non acid base Silicon. Personly I don't like silicon and presonaly I don't see this as being any better than the paint. When paint lets go, it is because the corrosion has happend under the paint layer not through it. But I may be wrong, so post your findings in the future.

I do hope this has helped

[ribbony]

We have been working on the rust issues on our vessel, so far we have found the Phosphoric acid based metal cleaner to be good after wire brushing, it gets it back to white metal. We have used a phosphoric acid based rust converter on our trailer and found it good, this time on the yacht we are using a tannic acid based product "fertan". It works the same by converting the rust into a relatively inert hard compound that you can paint over. If you use fertan then you do not remove all the rust as it need a thin layer to work. If you can access an area then using an acid removal then priming and painting is probably the best solution. If it is in tight spots the converter may be more convenient.

Chris - I can see from your photos that you are on a similar sort of project to ours. We are trying to work on an area at a time and bit by bit we will progress through the vessel. We live 400km away and can only work in bouts of a week or two.

Our Keel is the challenge, I think we have a resonable plan. We would like to have had lead in there but there is an awful lot of steel, at the expense of having in keel space for tanks and storing chain, etc. So long as the vessel is stable with that ballast then we will stick to it.

We like the idea of non petroleum based oil in the keel, for the environmental reasons and we can readily get vegetable oil in bulk working in the food industry.

We know that the fertan would work on the steel in the keel, but the concern was what would the acid do to the cement.

Cheers

Mick

[GordMay]

Apparently, tannic acid can cause corrosion to unprotected metals and concrete.
Acetic, Carbonic, Formic, Lactic, Phosphoric, and Tannic acids all disintegrate concrete slowly.

You might try searching the Portland Cement Association website: Concrete Technology and Construction | Portland Cement Association (PCA)

Or seeking a copy of:
“On the analysis of the Mössbauer* spectra of the rust converted by tannic and phosphoric acids”
by
C. A. Barrero Meneses, J. F. Ríos, A. L. Morales Aramburo, A. Bohórquez Gallo, G. A. Pérez Alcázar

* Mössbauer spectroscopy is used extensively in the study of corrosion.

[viking69]

hey mick,

well being a boilermaker by trade unfortunately i have had a bit to do with rusty old steel over my life any way if i was to own your yacht i would get the keel tested for thickness all over. get a thickness tester if you can as they are dead simple to use, you just zero them, then sand back to clean steel in small patches about the size of a 20 cent piece and about 100mm apart in each direction, put the tester on and it will tell you how thick it is. if it is within a suitable range then i would fill the keel with fish oil or similar..... definately not petroleum bassed oil. then just check the keel eack time it is out for antifouling etc.i would repair any of the rust effected areas properly otherwise it could come back to bight you in the a*s make sure you check the bass of the keel well as i would suspect that is where the problems will start or in any weld or join lines.

[ribbony]

So, I guess that thickness tester is an ultrasonic device. Bet they dont have them at the local hire yards. Will ask at the welding suppliers to see if they know where to look.

We did some test drilling near the bottom of the keel and it was all 5mm, however we should go right for the bottom plate and seam as if there was water in the former fuel contents it would have gone to the bottom in any case.

That is interesting & natural I guess with the acids eating the concrete. We might forget about that part of the treatment. That is where these forums are great, you get lots of angles and information that I would not have thought of in a million years.

Cheers

Mick

[viking69]

if you have a boat yard or shipwright near you that you are buying a bit of gear off hit him up as they almost always have one. if they have one offer him a carton of beer to borrow it that almost aways works :-)

[Alan Wheeler]

A thickness tester for steel is magnetic. Ultrasonic won't detect a thing on steel.

[viking69]

Originally Posted by Alan Wheeler

A thickness tester for steel is magnetic. Ultrasonic won't detect a thing on steel.

it is not the subject of the initial topic but i disagree. see attatched link to one of the many thickness testers. After all they do work on Stainless which is not magnetic.

Prosonic Ultrasonic Steel Thickness Gauge

[Alan Wheeler]

OK I stand corrected. Thanks for that. Now that I think of it, sound transmits through steel just fine so I suppose usign sound to determin thickness is a very good way of doing it.
Although if I may add and it's not trying to justify myself, but a metal does not have to be magnetic to be able to be picked up. The magnetic tester works similar to a metal detector. It simply uses a magnetic feild and the metal being tested alters that feild in such a way that the meter detects a difference in the signal.

[viking69]

yeh i sort of thought of that after i wrote the last post as well.

[Boracay]

I may be stating the obvious but I would imagine that provided all plates, frames, ribs and stringers were of sufficient thickness to provide structural integrity, watertightness and some allowance for future rust then the worst has been provided for.
If the rust is limited to only a few bad places then drilling may be sufficient.
There is no price on the sites I saw for thickness meters but one may give a lot of peace of mind.
From memory it is not uncommon for older steel boats to require some items to be cut out and replaced.
For your keel it sounds like you are not happy with it. It is really your decission as to what will make you happy.
Adams plans are still available so you may be able to discuss your position with the agent who (if memory serves me correctly) is a naval architect.

[GordMay]

Ultrasonic thickness gauges use a high frequency, short wave sound wave to measure wall thickness.
Different types of materials have different inherent acoustic velocities. (sound travels at different speeds through different materials ).
For example, the acoustic velocity of steel is 0.2330 inches/microsecond and that of aluminium is 0.2500 inches/microsecond. Coatings, such as epoxy, paint, etc, have an acoustic velocity about 1/3 that of steel.
Even if you don't know the acoustic velocity or your material you can measure it with the gauge, provided you have a calibrating sample of material of known thickness to start with.

Expect to pay at least $500 for a basic “economy” model, or much more ($800 - $6,000) for more advanced models.

An Ultrasonic Wall Thickness Gauge Comparison chart:
Ultrasonic Wall Thickness Gauge Comparison

[Brent Swain]

I once sandblasted the inside of a 36 footer . For blasting the inside of the keel I cut a 6 by 12 inch piece of plate out of the aft bottom end, for the sand to drain out. I blasted the piece I cut out, blasted the inside of the keel, then welded it back in and sandblasted the weld. It worked well, without the accumulation of sand becomming a problem.. The sump you described could easily be copied in stainless, and welded back in.
Brent