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Thread: Corrosion Repair

  1. #1
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    Corrosion Repair

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    Had been posting to a thread (Learning to TIG) now lost in the bit bucket. This boat is 1/4" aluminum, had "D" shaped rubber bumper bolted just below the top rail. Originally must have been some compound between stainless fasteners and AL hull, now long gone. Pictures tell a better story, I have been scratching the surface for more than a year. Long story short I am close to attempting the repair, thanks to all who responded to my previous thread, would never attempt this without your years of experience and willingness to share.
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    Re: Corrosion Repair

    Here is a practice coupon and the first patch ready to tack. I removed any material with nominal thickness less than 3/16 after grinding out worst of the rot. Some places will not be as easy to remove so I may stack beads to build up locally. I read about SASKWelder using this technique in tanks he was repairing.

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    Settings;
    1/8" electrode 2% thoriated
    Argon/helium mix, 50%
    High Freq ON, Amps to kill

    Have been working with onsite safety and local Marine Chemist to safe the fuel tank, it is three+ feet away.
    Last edited by _Dom; 03-02-2018 at 05:42 PM.
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    Re: Corrosion Repair

    Welding aluminum with corrosion is a pain in the shorts. The oxidized pits really need to go. If you have problems with that patch you might have to cut back further to better metal.
    Sometimes if the pitted metal can't be completely eliminated (still solid, just pitted), spot grit blasting can at least get the oxidized crud out and the welding will go much better.
    Ernie F.

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    Re: Corrosion Repair

    _Dom,
    couple remarks about the topsides corrosion band you're showing in the photos posted.

    #1 the extent of the corrosion shows this was not isolated to the galvanic cell of SS bolt to aluminum- other wise the corrosion would be localized and centered on the bolt holes- which seems not to be exclusive case?

    The widely separated but nearly uniform corrosion pitting also shows the type of corrosion was probably A) rubber (carbon "galvanic") to aluminum corrosion or B) crevice corrosion where the film of water DE-aereated and became acidic (in ph) and that (now acid film of 'water') attacked the aluminum stripping the oxygen from the oxide film and every time it got wet the cycle renewed- like recharging a battery.

    #2 since the corrosion pits of this type can be 'cavernous' or have a subsurface volume larger than the surface- that is: the pits may be larger just below what looks like 'sound' metal? This makes welding any kind of bead hard as the bead can 'explode' as the water vapor trapped in the subsurface heats to steam and the bead splashes all over- leaving holes in the welds, and the metal.

    so... as has been suggested blasting will help but.... I'd use acid etch like Zep-a-lume to excavate the pits with a strong acid and rinse the entire surface (if you're set on keeping the damaged metal??) and then assess what is left to 'repair'.

    #3 In the end you will find it a better solution (IMO of course) to simply cut out the entire band of corroded material 1-2' strips and replace the entire band of corroded material with new metal. The welding would be different but the result is a (potential) recovery of the boat; the method you show will prolong the useful life but you're not doing anything to address the widespread and still active corrosion cells.

    Good luck with your project,

    Cheers,
    Kevin Morin
    Kenai, AK

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    Re: Corrosion Repair

    metalman21 - Agreed, going to be an experience we call "good training". Might even devolve into Super High Intensity Training if I don't do my homework! Grit blasting is an option I originally thought to be too much trouble but I do have a setup that would be worthwhile to try. Actually hoping chemical etch will do the trick.

    Kevin - Thanks for your detailed reply;
    1 Agreed the corrosion extends well beyond the ss bolts and washers. Anything in direct contact with the rubber has been affected to varying degrees. Remembering a triboelectric chart and recognized the galvanic action between rubber and AL. Crevice corrosion was a new concept for me, thanks for explaining it in terms I understand. I am considering options for re-installing the bumper, aluminum bolts, teflon wide area washers, a spacer strip between rubber and AL gunwale. Gotta get an acceptable repair first.
    2 Have seen this in welding patches into a much thinner boat, I have been pretty aggressive with the grinder and will watch closely. Not me that is set on keeping the corroded metal, my goal is to not embarass myself with an ugly repair. Trying to ignore the voices in my head shouting "never start a vast project with half-vast resources".
    3 Have proposed a variety of solutions in descending order of preference; Very concerned about warping this rail I cut away too much. Any way I look at it is a lot of welding.
    remove top rail and 6" of gunwale, replace with new AL plate, top rail and install new rubber bumper
    remove top rail, repair corroded areas, install AL doubler and new top rail, re-install rubber bumper
    repair corroded areas, re-install rubber bumper. Watch for additional repairs to be required in short order.

    My biggest problem besides not qualified for this repair is proposing options when the decision-makers ask, "Can't we do this any cheaper?" I keep getting deeper and deeper into this hole, no matter how much I dig!?!
    Prolonging the service life will satisfy my boss, addressing the widespread corrosion is required. Hoping that a good etch, quality primer and epoxy top coat will provide a few years. Normal conditions would have me asking for the topline repair, half the cost of a new boat. We are extremely cost conscious these days so i am exploring lower cost options.
    Thanks for all your comments. Much to think about!
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    Re: Corrosion Repair

    Kevin - Sad state for what was once a fine seaworthy workboat. Due mostly to lack of experience of "owners" and lack of concern of "operators". Seems to me I had several conversations over the years with "maintainers" regarding proper care and repairs with nothing to show but this mess as a result. Several years I had respectfully declined to be welding on this boat considering my own lack of experience. Having survived a serious downsizing, now I find myself last in line. I am looking to salvage whatever useful life might be available. In the meantime I have learned to weld aluminum to an acceptable level and expect this experience will add to my ability.
    This boat was never really out of saltwater, might have been hauled for bottom paint once based on casual glance at the records.
    Under deck space hadn't been opened in considerable time, the hatch itself was deteriorated to a point where extraordinary effort was required to remove. Must either be replaced or extensively re-worked.
    Nobody who quoted repairs liked an acid wash, this is California. I remember welded AL boats are everywhere when I visit your great state, is this a common treatment in your experience? Would this be possible internal to tank ? I am already concerned about not properly neutralizing etchant from nooks and crannies when spot treating the areas to be welded.

    I expect the sequence is etch, neutralize, weld, prime and paint. Isolate the rubber and fasteners when re-installing rubber bumper.
    Will begin annual effort to re-assess the corrosion, replacing top rail at some point, possibly adding re-inforcement as that edge is compromised.

    Should keep looking for that camera to inspect tank internals. As I pumped at the last of the fuel I looked closely for water, surprisingly clean. I assume that means I have not removed all residuals yet.

    I keep procrastinating this job, rather sweep the parking lot. Every time the crew that drove this boat without taking care of it asks "when will it be finished" I add another six months to my assessment.
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    Re: Corrosion Repair

    OK, after finding this thread, I see the answer to my question on the other thread about the strange holes. I can't imagine replacing the top 6" to be "half the cost of a new boat" and that's what I'd do and if the client didn't like that idea it would be adios!

    Down-and-dirty could be a band-aide of plate wide enough to be tacked on the outside down to 'good' metal. If you didn't use 6061 that would last many years, and yes, would be another vector for mischief. But hey, it'd be fast and cheap. I wouldn't weld it continuously as that would just hold water. Your wasting your time in any case by not replacing it all. This offered with the obligatory, "IMHO."

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    Re: Corrosion Repair

    Yofish - for awhile I was shocked at the quotes. Job was bid by measuring weld seams and charging by the inch. No doubt it is a fair estimate, TBH I looked at original purchase price, 14 years ago. New replacement hull expected to be much higher. I hesitate to cut the whole top rail off and try to weld in new, controlling warpage is not a task I understand.
    My first guess was to rent a wire feed but everyone who looked at it said TIG was the best way to handle the hidden corrosion, even after aggressive removal effort I anticipate many surprises as described so well by Kevin upthread. If this first batch of 12 patches ends in epic failure we will be re-considering complete replacement of top rail
    Lift outboards and install a new hull starting to seem like a reasonable alternative.
    I will take an overall picture to provide a better perspective.
    Last edited by _Dom; 03-06-2018 at 05:13 PM.
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    Re: Corrosion Repair

    _Dom
    quick primer on acid etching for your reference. There are lots of commercial etching agents/compounds for aluminum, one of the most effective is Zep-a-Lume by the Zep chemical co. Its designed to wash/clean/descale tanker trucks including all types of tankers. There are many commercial yards (maybe not in Kali-forn-kneeyuh?) where this service is performed for highway tank trailers.

    Zep is a mixture of phosphoric, hydrofluoric and sulfuric acids that can be diluted but really cleans aluminum well - but all acids can simply be diluted to near neutral ph and DO NOT require neutralization- just water dilution. Acid discharges are regulated by ph- if the ph is nearly 7 there's no issue with discharge- otherwise vinegar would be a hazardous substance!

    So first point is - you may find a commercial trucking yard who can do this work- etching- and rinsing and returning the boat to you?

    But with a weed sprayer and a full rain suit, including painters' hood, air purifying respirator, double gloves, rubber boots and splash goggles- you can etch any part of the boat including the entire bilge- AND then just rinse till the cows come home. after you etch and rinse - you can repeat as needed- and this boat needs it!! but a yard sprinkler will rinse it!

    https://www.amazon.com/video-boresco...eo%20borescope these cameras are not really expensive or hard to find these days!!! IF the fuel cell you show has been tended like the rest of the boat- this is a wise tool to employee.

    Unless you let the gas removed from the tank settle overnight in a glass beaker- you can't convince me there wasn't water. It would be in an emulsion from pumping!! I wouldn't expect to see it without coalescing and separating out of the pumped gas mixture?? So I'll still wager the tank is about to drip gas- hope I'm wrong- but only looking inside will help confirm or deny the internal state of the plate.

    Next, Yofish and I are not ganging up on you- believe us, we've been there and tried to repair the swiss cheese cum aluminum you show and "It Ain't Happenin' " Yes there may be an inch or two here and there that will TIG float but there is no way there will be any seam integrity- you have lost too much metal.

    So.... as Yofish has mentioned to you- get a 6" or 8" wide sheared pieces (3' to 4' long) or strips of 1/4" 5052 and fit to the pipe and below the deck weld seam bulge- polish the bottom 1/4 of the pipe with 3M Scothbrite buffing pads after you acid etch the upper 12" of the topsides.

    To put the plate on- DON'T WELD or TACK- yet. Use self tapping screws to put the plate on the junk- after sanding blasting/etching and only when all the plate is screwed to the junk strip below the pipe cap rail and the deck- then go back and layout the welds

    Mig will do fine as TIG will be very slow and is not needed IF>>>> IFFFF the pipe's lower edge and the topsides below the deck is sound? Just stitch this plate in place over the junk/cheese/rotted out section. A 3" MIG weld every 6" staggered top and bottom will suffice IF>>>> IFF the pipe is sound and the topsides can be used to lap weld this plate too.

    After the plate is welded/stitched over the junk bulwarks- get is painted; etch allodyne primer and epoxy- not topcoat finished- use coal tar bilge paint as bedding for the new rubber bumper. There are several rubber shapes that have a D and flanges- you could run an angle below the pipe (stitched) to hold the upper flange and then when the rubber is clamped in place- clamp and then weld the lower angle over the flange- flooding with a hose when each weld is done will allow the rubber to live through the lower angle's welds being added while the D flanged rubber is under the angle.

    If you have to go with bolts again (poor choice but sometimes the only one available) then get PEX tube or other concentric plastic as bushings for the bolts and use HOT DIP Galvanized bolts- NOTTTTT SS as the zinc is much closer to the aluminum potential on the galvanic scale ( HEY!!! what do we use to protect our hulls from stray current corrosion??? zinc right?) so hot dip will be more stable and likely cheaper by far than SS.

    2 8" strips of 1/4" 5052 sheared out of sheet, 30' long -- then fit to the lower pipe shape, screwed on and then finally welded- is only a couple days work for two men. Long legged vise grips (12" w/ swivel pads) will hold most of the short planks together- a bandsaw will rip any contouring needed along the upper edge- and the screws will draw up the cover sheet to the old hull tight enough to well. who cares about holes in this field of Swiss cheese?

    Inside of the hull where all the bolts will end and have nuts- using zinc fender washers will last much longer than SS.

    Down and dirty Yofish said, I'm just filling in the dirty details- not too much work if done with MIG- a pain in the calendar and welder's stern if done by hand dip TIG!!!

    Cheers,
    Kevin Morin
    Kenai, AK

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    Re: Corrosion Repair

    Keep the ideas coming, not feeling ganged up on at all. Much appreciate the wisdom freely shared on this site, will never be enough time for me to learn all my own lessons empirically.

    Looked at ZEP-A-Lume, locally available and within our budget, seems like the right answer. I will drag this boat to our wash rack and have at it. You mentioned Alodine after etch, will have to be more careful with that. Looks like JOTUN no longer offers coal tar but Rust-Oleum does, I like this instead of a thin layer of nylon strip when attaching the rubber. Using PEX sleeves on the bolts is another great tip

    I should have let the fuel sample settle, will do so if I get more out of the tank adjusting trim/heel.

    Definitely will be getting a good look inside one way or another, thanks for the link. At those prices I have been wasting time looking for my camera.

    I have boxes of nylon bolts and nuts we use on the oil containment boom but they are not strong enough for this bumper install. HOT dipped Galv fasteners are top of my list. Doubt we will be replacing this bumper so weld on is not an option.

    Good point about zinc anodes, quick online search turned up weldable style with aluminum inserts, not sure how to specify something to weld to this hull?

    I have used self drive screws to eliminate gaps, didn't think of it but you are right who cares about a dew more holes.

    Unfortunately that pipe top rail is shot, rubber was tight against it, galvanic/crevice corrosion all along the bottom edge.

    Ultimately it needs exactly what you both said - "2 8" strips of 1/4" 5052 sheared out of sheet, 30' long -- then fit" not to existing top rail but to a new piece of pipe, welded on the bench and then attached as described after removal of existing swiss cheese.
    Last edited by _Dom; 03-07-2018 at 01:06 PM.
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    Re: Corrosion Repair

    Lots of good stuff from Kevin. BTW, remember that all of those etching fluids create hydrogen gas. If they happen to drain through a crack in a void.......

    I will boost the galvanized fasteners - SS is just steel that doesn't rust! Zinc is next to aluminum on the galvanic scale. They do, however, degrade over time as the plating sacrifices itself and thus need replacement. I have twisted off many 1/2' SS bolts running through pad eyes and never a galvanized one unless it was actually rusting. It is amazing the pressure created by the oxide expansion when SS is employed. I cannot begin to describe some of the horrors I've seen caused by the bad notion that SS and aluminum are compatible.

    I can imagine that even not being able to weld the top of a band-aide, that with enough backing (large washers or another band) would hold up well enough skip welded at the bottom.

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    Re: Corrosion Repair

    Thanks Yofish, another for my list of "things to avoid".
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    Re: Corrosion Repair

    Yofish, _Dom, while acids due give off hydrogen momentarily- the reactivity is limited to a few minutes- once the acid gets sufficient oxygen from the aluminum's oxide film- the acid isn't reactive to speak of. And, when you flush with water the dilution is so great that the ph shifts back to near neutral- so, again- reactivity is short term with the resulting effluent/flushed/rinsed off solution non-reactive.

    As to penetrations into cracks- this is actually a good thing while the acid is active because of the small excavation or surfaces of the sides of the crack. This corroded material is dissolved to some degree and the rinse/flooding then can flood out the debris, now turned loose from the metal's surfaces.

    Pressure washing after etching can help clean as the power of the water (or add some abrasive) can help lift residues left in pits, cracks, and other corrosion sites offering the metal a change to "heal" by forming a 'clean oxide' film of bare aluminum with atmospheric oxygen- forming the needed protective aluminum oxide film that gives the Miracle Metal is most prominent commercial property- corrosion resistance in air.

    _Dom using acid etchants is a task requiring care-(and lots of PPE!) it still is the low cost way to clean this boat- blasting would be better!- and can be applied anywhere you can get the spray and rinse spray.

    Cheers,
    Kevin Morin
    Kenai, AK

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