Metal Marine Tanks (mainly welded aluminum)

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gap998
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Re: Metal Marine Tanks (mainly welded aluminum)

Post by gap998 » Thu Jan 21, 2016 4:19 pm

Tom is not a welder! Were are the spatter burns on his forearms? I've never seen a welder with fingernails like that! :lol: :wink:

Great thread - Keep 'em coming.
Gary

Planning a whole fleet, but starting with a Zip...I think.

"Just when you think you've made something idiot-proof, someone builds a better idiot!"

Kevin Morin
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Location: Kenai, Alaska

Re: Metal Marine Tanks (mainly welded aluminum)

Post by Kevin Morin » Thu Jan 21, 2016 8:01 pm

gap, yeah Tom was a male model (software version) who was drafted in the welding poses- Hey! he's a model right?

Glad you still hanging on here, the key-hole welds need some notes too.. if anyone takes time to follow all this- their welder will be making job offers as fitter before the tank is done!

cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
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Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Metal Marine Tanks (mainly welded aluminum)

Post by Kevin Morin » Tue Jan 26, 2016 6:13 pm

Small details can (will) contribute to the welders' quality of work and his opinion of working with you in the future; good prep, clean well marked, cut and fit material and sequences of work all laid out will make a better relationship than dropping off a box of cut parts and expecting a welder to be able to understand what you planned.

Keyhole welds, pocket welds, some even say socket welds but that confuses with a type of welded pipe fitting of that name, are welds where a hole is put in one material and the two materials are stacked and a weld inside the hole on the top sheet; holds the two pieces together. Sort of a welded bolt or rivet - a single point of fusion of the two metal pieces. This is a completely legitimate weld joint type, but a picky one, and especially picky if you aren't a welder and therefore ignore what is about to be shown?

We've talked about the arc, not that tank builder is necessarily going to weld, but; we needed to explore the Why of some joints for reasons we've shown above. This post explores another small detail that can come back as a problem in a tank build and cost you shop time that could be avoided - if this information is incorporated into your build.

The subject is the preparation the keyhole or pocket welds' joint prep. Specifically, we'll explore the walls of the holes cut in the top material; these walls should be conic/flared out/wider at the top than bottom and hopefully we'll all agree why that is the case.

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This sketch, above, is of two pieces of tungsten, the non-consumable electrode used in TIG welding to provide the arc and therefore the heat of fusion of the aluminum. NO gas cup is shown, no argon gas cone is shown, and no filler wire, this sketch introduces just the two arc cone's proportions.

There are two blue cones of different proportions coming off the sharpened points of the electrodes and their different proportions are from the angle of the ground tips. Notice one electrode tip is more like pencil, sharpened to a longer cone that the right side - blunted cone? The more blunt the cone the narrower the arc, the sharper the tip is ground the wider the cone of the arc. We don't care why that is true, but it is. What we do care about is how this can be a problem for our weld preparation?

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All the holes in this sketch, above, have vertical sides so the top and bottom are the same width. The smaller hole to the left would have to have a pretty narrow arc cone to reach down inside and melt to the yellow angle extrusion's top surface in order to make this keyhole weld work. The weld should start at the bottom edge of the top material where the two parent metals come together.

The wider hole may allow SOME arc cones down inside- in other words the wider hole may be the solution but you can't control how your welder grinds his tungsten, and even with a narrow arc width from a blunt ground tip... the arc may not reach the bottom of the hole.

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IN this third sketch, our view point changed down close to the plane of the work, to see what the problems can be. The arc cone has 'swung' or wandered to the side of the top materials, the arc is finding the closest path to the welding arc Work connection to the welding power supply (sometimes called 'ground' but the is AC TIG so that term is not too useful). When the arc wanders to the top side edge; it will not direct heat onto the top of the back up material first. That arc wander happens because of the two features in this image.

First, the arc cone may not 'fit' down inside the hole for the weld and (Second) with the shoulders of the drilled holes closest to the electrode there is a natural tendency for the arc (even of narrow arc cones) to heat the sides of the keyhole first! NOT GOOD.

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What is the solution? This image shows the smallest hole, left, that has be made into a cone instead of a cylinder and the longer weld to the right has also been widened at the top surface edges.

Now the arc cone, even a wider cone will reach the angle extrusion's surface before the top edge of the sheet is melted. This allows the welder, even if using a MIG welder (not preferred for this weld but 'doable') to melt/fuse/weld at the boundary between the two metals- first. Each weld will be initiated on the back-up material's upper edge edge and the conic shape of the hole's sides allows the lower edge of the two materials to be fused first, building up to the top of the weld last.

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This last sketch in this series of 5, above, just closes in to show each arc cone can now reach the bottom material and the lower edge of the top material to initiate the welds; instead of being hard to control and 'running off' to the top edges of the top material.

The areas under the arc cones now, are the edge of the two materials, before there was no assurance this could be accomplished? Both MIG and TIG arcs will wander to the closest 'shoulder' of a drilled hole and therefore fusion of the bottom is in question.

I'm sure if you're not used to welding these types of welds, or have done them but simply made bigger holes in the top sheet to 'get down there' ?? you're probably wondering why this matters in a tank builders' set of methods of work?

The reason is that if the welds are not initiated down at the two materials closest edges, where the meet at the upper surface of the back up material- then the line of fusion in the entire keyhole weld is faulty and the weld may fail- pop loose- come undone! IF the top surface of the back up material is not seen (in the welder's hood while welding) to fully melt and fuse to the lower edge of the sheet overlay(?) then the chances of failure are too high too accept.

Where do these welds happen? They happen on tanks that have a top added last, where one sided welding on the perimeter seams is common, but there are sufficient structural elements, like baffles for example, that remain to be welded to the top. In order to fuse the 'field welds', which are not part of the top's outside seams, keyhole or pocket welds are used to weld the tank top to the structural elements inside. (also used to put decks in welded boats)

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Here's a picture of a router bit that will do most of this work- the beveling work not the hole drilling work. This type bit can be run with a top table guide on the base to keep the router in a given hole, elongated or not, and also with a bearing guide from below, clamping a plate with an over sized hole to guide the bearing under the work piece.

Why not just make the holes big enough to get all the different types of welding done done inside a bigger opening- why bother to bevel these keyholes' edges? The reason is to keep the keyholes as small as your welder will accept them. These welds will 'pucker' the tank top (any panel can be distorted if these welds are not put in correctly), the larger weld can more easily have a crater crack in the center as the bigger puddle cools more slowly and the "arc core" may not be cooled to solid before the weld top is cooled (cracking) and that will leak in the pressure test- then leak fuel.

What happens when the tank is pressure tested? Some or another form of soap is spread on the tank and you look for bubbles. Then take the pressure off, and TIG the "leakers" . But its not that easy... the soap gets into the leak and now the amount of re-work gets bigger as the welder has to carbide burr out the crater in the keyhole and reapply the weld, what if it leaks from the soap contamination down in the weld metal... well the result is sailor like language by the welder about your Mother! Not that she has his profane rant coming, nope , just that the welder is frustrated by having to do this work again, and possibly again, again.... and you're paying for that time too!

So if the tank design is large enough that entire panels have to be put on where they need to attached to the interior structure, like baffles or supports, AND keyhole/pocket welds are used; consider taking the time to make each weld #1 the correct diameter for your welder's preferences, #2 bevel the sides to allow the welder to reach down in the weld to start without arc wander and #3 done once, correctly, each weld will probably test tight, and the work time to weld your tank will be reduced or conserved.

A hand held die grinder with a conic or pear shaped carbide burr will bevel the edges of these holes as well but are sometimes less controllable depending on the bit to hole size ratio.

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This last photo in this post shows keyhole welds holding a piece of a skiff deck to the framing. The deck in this case is an air tank, and was pressure tested to 3PSI to insure the integrity of all the welds. All the keyholes were bevel sided and none leaked because they could be welded in the correct sequence- bottom up to the top, cooling at the top and then stopping the arc on TOP OF cooled welds that were fused from the bottom first.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
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Re: Metal Marine Tanks (mainly welded aluminum)

Post by Kevin Morin » Tue Jan 26, 2016 11:57 pm

I happen to have some tank build sketches and photos that can help expand out design ideas and I'll post some of them in this article. The reason to look at this tank in our 'how to' series on welded tanks is to understand tanks can be more than a plate box. In this case the tank is located too far forward to be 'out of the way' but the owner wouldn't let me put tank(s) on deck under the sheer clamp (darn it) so I had to come up with some location that would get the tank off the transom.

I might have gone under the decks, but those tanks are lots of work, and if they need any future attendance- well they have to be cut out usually, something the owner was not enthusiastic about even discussing. Where to put the the tank?

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This is the concept sketch for the cabin and the tank is part of the bulkhead (dodger) of the cabin. The curves help to make the cabin's forward shape more attractive, stiff with less reinforcing and 'hide' the tank. As time went by the owner decided on less and less fuel so the final tank got smaller and smaller, but it was built along the lines shown.

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AS this photo above of the lower cabin sides and curved bulkhead being tacked up show, the tank will occupy the lower part portion of this three cylindrical rolled piece of 0.125" 5086 aluminum. There are two matching corner rolls of 6" radius cylinders ending the longer radius cent arc of a bigger cylindrical section.

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to stabilize the outer shell or forward sides and end plates (all one piece) we needed to fit the top and bottom because the piece was flexible. These angle extrusion clips will hold the blank stable as we mark the shape. It was too flexible.

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What looks like I've tacked welder to a couple of 2x4's, in this photo above, is not true. There is a small piece of aluminum dry wall screwed to the spreaders' ends and the tacks are to the metal that doesn't show up in the photo very well. NOW the top and bottom panels were held in place and scribed and cut.

For a description of how I mark reference lines, scribe them and then cut the companion thread on building techniques goes into detail.

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In order to support the wt of fuel off the deck on the 0.160" bottom panel a full width baffle and structural plate is seen on edge in the middle of the bottom and baffles which are also the interior structure as cut and fit to the bottom. This 6" x 0.160" flat bar is 'limbered' on the bottom edge to all fuel to equalize at low fill levels, then it has notches fro the baffles to allow them to aligned easily for tack up and there are also full 2" holes to make sure the tank will equalize at 3" level fill in case the lower limbers are too slow flowing? When stitch welded the entire length this 6" bar will be the primary structural element in the bottom panel in this direction. However with all the baffles solid welded to the bar, and stitched to the side panels... the bottom is more than strong enough to hold a few hundred pounds of evenly distributed gasoline.

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This photo, above, shows the tack sequence of the bottom (baffles under the front shroud in this view) along the lower edge of the tank.

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The tank is standing up on a set of horses, we're looking into the tank as its tacked and there is Sched. 80 water bottoms sump that has a 1/2" plate bottom plate. IF there is any water bottoms corrosion in this tank it will take along time to eat 1/2" of material. The tank baffles' edges or corners "mouse holes" are visible- they show in other pictures but due to lack of contrast the corner cuts don't show well in the previous photo.

Almost all these welds will be done by MIG reaching into the accessible areas and welding nearly continuously. REaching over the 6" bar to back weld the bottom to front panel seam was somewhat difficult and not probably possible without the push pull type of MIG torch.

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In this photo above, the lower seam has been TIG welded so the inner or back up weld could be done before the back or cabin side vertical side could be added. This allowed a full back weld, but not one that would be easy for a novice welder, and most welders using a 1lb. style torch would not have reached the weld. TIG was key to doing a full fusion weld but since this weld was done on the bench it could have easily been done with a MIG torch out as well as inside.

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The back was put on using the same techniques explained above, the fill has a 2" down comer pipe and the fill neck is shown here in this photo.
The draw, sump draw and vent are all on the back of the tank so it could be plumbed to the inside of the cabin. The only photos of that are simply some 1/2 couplers welded to the tank!

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In order to keep the fill out of the way of the passage next to the cabin- narrow space- the fill was recessed using a small curved piece cut into the upper dodger shroud and then welder continuously. The fill itself if just an aluminum twist cap female weld-on fitting (air craft supply companies) welded in a miter to a short segment of a weld el butt weld fitting (1-1/2" I think?) and then welded to the top of the tank doubler that carries the downcomer/fill pipe.

What does this have to do with tank building? I hope to show that almost any shape that you can form metal into might become a tank? Seats, or seat bases, bulkheads along side the cabin or forward bulkheads, (not necessary to be rolled), removable forward or bow decks, almost any place in the boat you need to locate some wt : a tank shape can be designed to fit.

Is the tank 'legal'??? well it held pressure and so I expect it does its job, but it may not be 'according to Hoyle'? I've made hundreds of 1/8" sided tanks in the last few decades and they seem to work fine? Some will say they need to be thicker, I just need them not to flex- in any case at all. By rolling this large sheet into the sides and front of a tank I got the stiffness increased (tensile goes up in cold forming) and I got the shape and cut down on weld seams all with one fab shop rolling this sheet.

Even a console could become all or part tank! So, this post was about the idea of combining some of the elements we've explored so far, that are required of marine tanks, and combining them into a somewhat free form shape that does its job.

Many boats need to get more weight forward to help balance the outboard engine and since the smoothest ride is aft most of the people, engine and control rigging all end up somewhere aft the center of buoyancy so.. many skiffs will sit down, below the design waterline, by the stern. A 50 gallon tank weighs 300 lb plus the tank and hardware- say 350-375? that much weight, placed well forward can sure help to get her bow down. So finding locations that may be good locations may then imply you have to get creative in the design of your fuel tank?

Cheers
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
Posts: 699
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Metal Marine Tanks (mainly welded aluminum)

Post by Kevin Morin » Thu Jan 28, 2016 3:52 pm

This post is about tack welds, and will explore how they need to be understood in order to use them in conjunction with 'full seam' welds, as well as notes on the overall relation to tacking and following on to the final welds.

So far, I've been writing to non-welders who will plan to organize, supervise, plan and guide the building of their own tanks but here is information I might have put on the companion thread, next to this one, as these work methods apply to any weld seam in aluminum. So if you're a new boat welder, tank welder or even is someone is going to do your boat or tank welding for you (a completely reasonable arrangement given the cost of time and money to become proficient with the right equipment); this post gets down to details about tack welds handling.

Tack welds are simply very short duration welds that are used to put a tiny weld spot to hold aluminum in position prior to the final welding - regardless if the final welds are continuous or stitched/chain welded or patterned but not continuous welds. Tacks are essentially hot bolts and in stitch and glue wooden building methods are like the tie wraps or wires that are holding the joints before gluing/epoxying the seams. That is pretty where the similarities end, as tack welds can, if allowed, make the final seam weld low quality, especially if the seam weld is by the MIG process.

Do you recall that we've called a weld a related rate event? ( I hope I've said that before?) Like driving a vehicle; throttle, gear shift, steering wheel, position of hte windows, radio, heater and a few other items all need to be coordinated - related - as a rate of change to one another. So it is with welding; wire or filler into the arc heated puddle has to be correlated (related rate) to the amount of amperage and the travel of the gas cup with its arc and the rate of melting to cooling and filling while hot... and the angles, rates of flow of gas and... well! I hope that begins to paint the image of relating rates of different values (wattage, wire feed speed, travel, arc length... ) at one time to perform a weld?

Flying airplanes is pretty simple skill- but landing and taking off are much more difficult to master. Steady state 'related rates' once they're tuned and running - like driving over the Nevada desert at 55mph on cruise control- is much easier to do than to parallel park a 35' 5th wheel trailer into a camping spot that has only 2' of side by side clearance!

Welding either MIG or TIG melts the parent metals' edges of sides of the weld, we add some kind of filler to all aluminum welds so when the mixture cools the two pieces are welded. If the two metals are thicker or thinner than the last weld done by the same welding torch and power supply the welding adjustment(s) to attain a smooth related rate of continuous weld has to change to accommodate the change in the wattage of weld- required to melt and fuse the two parent metal pieces.

The adjustments used to weld 1/2" total thickness (2 pc. 1/4") is much 'hotter', higher energy, greater power settings than the same process welding two pieces of 1/8" or a total thickness of 1/4" aluminum. We're getting closer to talking about tacks, but we needed to make sure the next statement is appreciated for its contribution to potential welding problems.

Tack welds, as they are encountered in a weld seam, MAY act just like changing from 1/2" thick in the middle of a 1/4" thick weld! The tack will require MUCH more energy, a radical change in the related rate settings in order to perform an evenly smooth and equally penetrating weld. A tack weld, that is not properly dressed prior to welding is like asking a driver, in traffic, to travel at 35 mph, accelerate to 75mph for one car length, the resume the 35mph speed - oh ! and don't hit anybody while doing this speed up & slow down for one car length.

I hope I've painted a picture of how difficult tack welds an make seam welding? But there is a simple solution - dress or shape the tacks after they're applied and before they're welded. However, I cannot count or recount to you how many welders or new builders don't accept what we're about to explore as good trade craft. Believe me, this is how the better welders and fitters treat all tacks, all weld prep and anyone who produces really good welds does this, or some version of this.

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First sketch, above, shows a spherical tack on the outside corner of a tank, or the sheer of a skiff since the lower panel is leaning toward the viewer and the upper panel is more or less horizontal like the guard deck or sheer clamp of a skiff build.
The tack is a white-ish sphere that fuses both the two pieces together, the edges of the tack melted into the parent metal showing the tiny spot weld is holding the pieces together.

But the thickness of the tack means that when the seam weld settings were established, moving over the tack would leave the weld heat/energy/rates of melting too low to melt the entire tack AND the two seam edges. So the weld would either have to be stopped (in MIG with its continuous feed of wire this will lead to a huge pile up of welding material!) in order to fuse the tack (called 'burning out' the tack) or in TIG the welder has to stop feeding filler rod, keep the torch in one location and add some welding wattage to 'melt' that thick tack into the main weld, very possibly creating a 'hot spot' or a build up of weld.

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Step one, shown above of 'dressing a tack' is to cut the tack's over hang or bulge outside the lower plate- off. The 'cut' is easiest done with a hard sanding or grinding disk mounted on a small format sander but the "plane of projection" is what is critical in our discussion.

IN this 2nd sketch we see a blue plane in the same plane as the side of the tank (or skiff) that is what is left of the tacks' overhanging bulge that was formed during the short duration weld process. The cut is done by touching the tack with a hard wheel held in the same plane as the side or the tank or skiff. What often happens is: the new metal worker will sand a 3" wide area to get at the tack side! Not good tool use- the areas around each tack should be as small as possible so the 'grinder tracks' don't scare of the tanks sides, are compact and only touch the side very near the tacks -if at all? AND the edge of the parent metal is as intact as it could be without any tack or 'dressing'.

The skill and habit of doing these tack dressing steps are shown in order of best = almost no grinder tracks to lowest = sanding the entire edge of the tacks along the seam 2" wide!!! (arghhh! amateur hour) If the parent metal edges are scalloped by over sanding or poor tool control the weld will be compromised as the edges of the joint shown are the guides for the related rate and uniform cross section of the weld in that seam.

Readers, this last few paragraphs cannot be emphasized enough if you'd like to produce quality tanks or other fabrications.

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Here in the third sketch in this series the top bulge has been cut/ground/sanded/removed with the same guidelines. As close to the surface as possible, while remaining in the plane of the top plate, with the least tracks along side the tack digging into the parent metal as possible.

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The bulk of the middle of the tack weld is not doing any active 'holding' between the two parent metal parts- but this section of the tack can surely add to the mass change once it is crossed by the seam welding process- so lets get rid of any extra metal that is not 'working' to hold the two pieces together before the seam welds.

IN this sketch the tack has bee cupped using a carbide burr on a die grinder (air or electric) with the burr shape being a 'pine cone' or 'pear' or cylindrical bit, but only the non-ferrous types we're discussed before.

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Last sketch for the tack dressing discussion, above, shows the summary of tack dressing sequence. I suggest it is good practice to cut all of one side or surface on the entire job before moving to the other surfaces or the cupping to reduce the cross section process? That may be just my method but I like to get to one technique and use it along all seams, then retune and position for the other two processes- but the work is tedious, requires practice and is the only method to get high quality seams in welded aluminum tanks.

Inside seams are not show, the reason is very often tanks an be more easily tacked from the outside, then the back welds have not tacks to dress before welding. Also, dressing inside tacks is all done in the last cut image (2nd above) by simply cupping the entire tack inside the fillet area.

Hope that you'd consider this work important to your tank weld process, your welder will! Now, what happens if you drop off your tank to be welded and you are not there when this process needs to be done? I'd suggest that if go over this set of details with your welder - you could agree to be there to help- no reduction in costs - you'd be free help if allowed- AND its possible that their shop insurance or work schedule won't allow you to be involved? Then, I'd ask if the tank could be tacked up to some agreed point- returned to you for prep and tack dressing and then... returned for weld out. IN the last case, if they see these sketches, and you discuss this with the welder- it is fully possible that a TIG tacked tank, will not have any of the overhang or MIG tack bulge issues and tiny tacks could be welded over without dressing.

Please let me know if this leaves questions about tack weld use and relationship to the seam welds? I use these methods in my tanks, and all the other tank builders I know, very few these days, do this as well. If they don't some of all of the problems I've discussed may occur but all those welding errors can be overcome by correctly dressing tacks before welding.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
Posts: 699
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Metal Marine Tanks (mainly welded aluminum)

Post by Kevin Morin » Tue Feb 09, 2016 1:59 pm

On another site, focused on welding, there was a discussion about repairing old or used tanks. I've shown above that my opinion and that of all safety minded people is: don't do it. If you're an experienced welder, have repaired or modified used tanks for years, have your safe work methods; OK fine. If you're not? please don't take this post as a way to become involved.

This post is showing why repair of corroded aluminum can be so difficult to do. If wood is rotten, or glass fiber composites are delaminated and saturated, repairing those hull materials is not only difficult; repairing in those conditions may not be realistic. This post, in the tank building series is to give another reason why old tanks maybe in a state that is beyond realistic repair.

Corrosion of the tanks' surfaces may happen inside or outside depending on the cause. We looked at chemical corrosion by acidic water bottoms, and mentioned there are other potential causes, galvanic (different metals) and stray current (instrumentation current wiring errors). Galvanic corrosion is rarely, if ever the cause of this series of corrosion cells in this post. However stray current AND chemical corrosion can cause these types of pits.

One last word in preface- I do know for we cannot see inside aluminum plates and sheets. I need you to add a little imagination to my sketches so we can all 'see' what is being explained in the images. I had to draw as though we could see inside metal- making the metal glass-like in transparency so the pit type can be shown. So for a tour inside a certain pit type, common in aluminum corrosion cells, the following post tries to help welders and non-welders alike to appreciate what could happen in tank (or hull) repairs.

The type of corrosion shown here is (I think) called a "cavernous pit." Most corrosion begins are a tiny location on the surface and that site's reaction are a concentrated version of the surrounding metal- so a pit site is initiated. A cavernous pit type is when the surface pit 'goes inside the metal'. A canverous pits' main top areas looks like good metal.

So, the welder turns over a tank that was bedded into the boat on an isolation matt that stayed wet- where a film of water was between the matt and the tank, which was not coated. The water has become stagnate, acidic and pitted the tank's bottom.

The welder may look at the tank and declare it can be repaired (he steams the tanks, washes the tank, purges the tank, checks the LEL, adds water or inert gas... and prepares to weld) but when he lights up on the pit site - the well of the tank greets his weld with mini-explosion ! The welder says things about the tank owner's Mother that are not true, he then finds another place to "repair" and the same thing happens.

When the welder finds a pit site, he uses a drill or carbide burr to drill out, the white chalk to clear metal sides.

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here, above, is a sketch of what such a drilled out pit may look like from the surface. The exaggerated black ring around the drill tip shaped cone of the excavation may only be dark gray or even a line around part of the conic excavation of corroded material?

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If we got down close to the drilled out pit site, we would see this ring down inside was more a layer of darker material. "And that spells Trouble in River City". That 'ring around the drilled out pit' is the indication of a subsurface (cavern) of further corrosion. And these are one big pain in the stern to get out, then welded up, the pressure tested and all that is implied in a reliable repair.

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OK!, imagination time; this image of the INSIDE of the aluminum plate, shows the original pit's roughly conic shape above a flattened out cavern that I've drawn as a horizontal gray 'box' much wider than the original pit's excavation. Here then, you're looking into the metal, with the lower surface of the top of hte plate above... and the upper surface of the bottom of the plate below, the aluminum is actually missing as I've used the sides of the plate as a box that we're looking into- the pit and its lower chamber are 'floating' of hung by the pits entry on top.

Hope that idea isn't too Sci-Fi to render the image confusing instead of clarifying?

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This sketch helps clarify the various images as a progression of views to show where the pit originates, where is begins to spread inside the plate under the surface and how the overall subsurface may look if we cut away the metal, then "looked inside"?

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In this sketch I've removed the pit and the pit's lower chamber (subsurface cavern of corrosion) out of the metal into our 'day light' so we can look closely at what I'm proposing is the actual architecture of this type of aluminum corrosion.

When the welder sees the top pit, he drills out the corrosion in the throat or original pit.

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Here, above, is a drill bit about to clean to bare metal- the pit's top showing original opening.

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And this sketch has the bit's tip reaming a pit at the top: this image leads to the first two at the top of the post. A conic shaped reamed opening in the metal that looks like it has a ring around the pit somewhere below the top.

NOW, for why this is a major pain to weld.

As the welding puddle melts the aluminum at or near the reamed and cleaned cone water in the cavern below boils and the steam escapes up the vent/throat/drilled hole and the cover gas, argon, is blown off the weld. AND to make matters worse, the steam bubbling up in the weld will almost always leave the weld with a holes, and the various other by-products of corrsion that are still in the pits' subsurface cavern will also combine with the weld to make a mess.

Now if the gases can't get out of the vent fast enough, but the metal covering the cavern below the surface is melted by the arc? then the entire are 'blows up' in a small steam created volcano of molten aluminum- hence the welders' sailor like language and increasing frustration.

I have found these type pits in several different attempted repairs. I have found a 3/16" dia. pit with a 50Cent sized cavern below. I have found ways to repair some sites, and failed at others. I have done this work overhead under a hull, and I've done it on the bench with more favorable weld positions and better rework of all welds attempted.

However, the reason to skip this work entirely is the same as the decision to rework wood or glass fiber resin composites; work versus gain? The level of effort to clean up many tanks' corrosion is more than the cost of building a new tank. The extent of pitting corrosion is not easy to estimate so agreeing on the work is almost impossible. If welder offers and hourly rate and 'as long as it takes' then the hours involved in fighting the pitting type I've shown above is very likely to make the tank owner unhappy.

The purpose here was to explore the esoterica of aluminum corrosion pitting so that welders and non-welders alike would be able to add to their knowledge about the pit-falls (!) of welded repairs for metal tanks. Not all pits are this complicated but... you almost never know until you 'light up' on that given pit if there is a cavern of corrosion spread out under the metal surface? One indicator is the drilled out pit's clean metal side walls; if they're not uniform, if any thing 'wets' the drill tip, if the metal is discolored in the cleaned out areas? In my experience; that's a good indication the "surface won't tell your what the deep water knows" and it's time to build a new tank.

Please recall I've tried to argue in previous posts that welded on used gas tanks is poor practice, this is just another reason to stress that idea. These pits make all the prep work (for the experienced welder) wasted. These pits are JUST another good reason not to weld on used tanks. Build new tanks- don't repair.

[FULL DISCLOSURE: I have welded on countless used tanks, one is above in the picture of the exploded tank. How did I learn about the pit types shown here, that I found on used tanks? I welded on them, trying to repair them and had some success but also ill will from owners who felt I'd cheated them on time, even when I spent the time I billed and it was agreed to be hourly rates prevail. However, you don't have to make these mistakes- you can simply avoid mine, as recounted here, and decide to replace instead of repair used fuel tanks?]

Next we'll have to take a box tank from beginning to install.

Cheers,
Kevin Morin
Kenai, AK
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Re: Metal Marine Tanks (mainly welded aluminum)

Post by Kevin Morin » Sun Feb 14, 2016 11:24 am

In order to review a box tank or rectangular form tank made of plate/sheet aluminum I'll provide some examples of one set of tanks done a few years ago to be installed in a fiberglass boat that was repowered at the same time.

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First photo, above shows the tank bottom plat, one of the main baffles and some of the shorted baffles of 3/16" that will form an "egg crate" frame work of the bottom. The tanks will hold about 100 gallons in their 14.5 ft^3 volume so that's 600-700lb on the bottom of these tanks. The framing of the main baffles acting as beam webs or plates to hold this wt. were: the two sides and two internal baffles so 4 lengthwise pieces of 0.160 or 5/32" 5086 H116 would be the main structure.

the side ways baffles would only have to be 3/16" plate up 6" or so to form an adequate bottom support for this load. The upper baffles would be filled in with other furniture as the build climbed to the top.

All the bottom plate supports were cut to interlock so they'd be easier to assemble, and when welded fully form a good lattice work of support to hold up the gasoline. All the metal was put through a rotary drum sander to remove the mill scale, and the tanks were etched inside and out before completion and painting.

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This photo shows the normal cup, curve and bow in coil sheet materials when purchased and cut into smaller rectangles. The notches will make clamping to tack up much easier for one man to do.

All bottom and top corners of all interior pieces are cut off to provide limber holes/mouse holes where the liquid can equalize level, allowing the tank to carry all fuel weight evenly during filling, draw down or empty states.

Added areas of cutouts allow for the tank to equalize level in a faster fill like a commercial boat fuel service where 2" higher speed pumps are the norm.

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A photo of the beginning of tacking up. By clamping the tallest (stiffest) longitudinal frame member to the bottom, tapping the shorter cross wise pieces until they're all even to the sides of the bottom, the first tacks can be added.

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One nice fact about box tanks is that all the interior pieces are straight lines. So the pieces can be sheared if time is important, or saw cut and held to the stationary belt sander to dress the cuts straight as an alternative. Either way, by clamping all the pieces to one another in a butt joint (shown) or as an edge to edge fit for the outer seams (coming up) the tanks' assembly can be reasonably quick.

For those who may approach a welding service to to build the tanks, regardless if you're allowed to work in the shop to help assembly during tack up or not (?) this kind of planning and pre-fitting will be appreciated by your welder, and it will reduce your overall time to build and therefore help conserve costs.

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In this photo the four sides are now tacked on, some minor stitch welding has been done on the lower most baffles/egg crate structural supports but most of the interior welding remains to be applied.

next we'll keep adding parts inside and welding out the interior.

Cheers,
Kevin Morin
Kenai, AK
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Re: Metal Marine Tanks (mainly welded aluminum)

Post by Kevin Morin » Sun Feb 14, 2016 3:31 pm

Continuing with a box tank build in photos.

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In order to weld best on straight seams with aluminum; MIG fixtures are useful, even for experienced welders, because the weld happens so fast most people's reflexes just don't keep up. I've welded for a long time (1970's) and the more I weld aluminum MIG the more fixtures I make.

If the welds are the critical path to building metal fabrications (no weld= no fabrication & poor weld= poorly built fabrication) then preparing to do the welds is important. In the case of tank work, I put the box type tank on a engine stand fixture (actually an oil field valve stand is shown) so the work is #1 easy to reach, #2 positioned the best for each weld ,& #3 almost all welds can be horizontal instead of up hill or down hill or overhead. All positions of MIG welds will work fine, but if you can roll a tank the welds are just faster and easier to put down.

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Depending your the tanks' size, getting inside to reach welds is critical to quality welding and if most of these inside welds were done at assembly stages shown in the previous post's photos, with no sides in the way.... the components would have been warped MORE than if the sides were added, and then the entire bottom and insider were welded.

Note for those welders reading; the two work leads are from two power supplies; one is TIG the other is MIG, so the welds inside and outside can be put in coordinating between the processes to minimize contraction distortion. Not all tanks would be assembled in this dual welding method.

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I've remarked before (I' pretty sure) about the types of MIG welding torches- this is a push pull type of gun. The motor in the torch handle is aligned to the streamlined torch allowing good access to narrow spaces without giving up good nozzle angle/arc control due to the torch shape.

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Same idea in this photograph; access to the egg crate or lattice work tank bottom support grid of welded plates and wide bars has to be planned depending on your welders' tools. If you plan a tank where the welder will use a T shaped or Pistol Style ("1 lb." gun) type of torch with the wire spool in the hand held body instead of in a remote cabinet (push-pull type as shown) then.... you'll have to review the welds, the sequence and the tools in your plan with your welder BEFORE you show up and things get expensive!

I'd say, a cardboard mock up, or even the metal parts with tape could help both you, as the tank designer, and your welder to resolve any 'issues' or 'questions' about weld access and help your design to be more easily built.

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Once the interior and exterior welds of the lower 9/10ths of the tank are welded inside and outside; remaining stiffeners/baffles/and plug weld back ups can be added.

In this image the two main supports reach end to end but not the top. Scrap or off cut pieces have been used to continue the bottom main bar supports upward and create wave suppressing plates while increasing the overall egg crate support matrix so the tank ends very rigid.

Both the fill down comer and the fuel draw are installed and have been MIG welded to plate struts to their nearest sides.

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IN this photo of the tank's upper spacers/baffles and top supporting angles, all pieces have been added to their nearest or abutting tank baffle or side and then welded continuously using the MIG torch.

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Same information as the previous photo from a different angle. The upper baffles on the short legs, are jsut butted to the two main longs, which are the primary strength of the entire tank as a "box to hold fuel". The added baffle plates above those welded to the bottom in both directions, simply stop 'free surface movement' (waves) inside the tank while keeping all adjacent planes of metal from being distorted or warping.

this post was to follow on the previous post and show the assembly of a box or rectilinear shape tank. The stages are to build bottom up, weld inside when the shapes will all resist distortion the most, work out the top, then drop on the top and TIG (one sided weld) around that.

Cheers,
Kevin Morin
Kenai, AK
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Re: Metal Marine Tanks (mainly welded aluminum)

Post by Kevin Morin » Mon Feb 15, 2016 4:03 pm

I realize these tanks are on the large size (32'er with twin Honda 225's) and that most Glen-L readers won't be taking on tanks this size but they remain the only set of photos of a full build sequence. I didn't bother to photograph 95% of my work while I was doing it. Who'd have thought anyone would care if I could explain how to or why I did any given step in building most of our work?

I'm still finding more buried image files resulting in more posts of this set of large tanks as I locate them, in my meticulously organized files.

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This is the only "adding the top" photo I can find! So the process of welding up the keyhole/pocket welds that are backed by the angle offcuts shown previously are all done! Great sequence on my part- sorry; the top is welded out in this photo but the fittings begin to show up. Each individual keyhole or pocket weld site was welded from the bottom to the top, then the entire weld was 'tig-floated' with a circular bead while the amperage was reduced so the arc core was on top of solid weld material below inside the pocket site.

TIG gun that I use is in the background. [Note: this gun is not very widely used, most welders don't believe it even exists so don't plan to discuss this torch's use with your tank builder.] However a tank top like this one, using two hand TIG is an hour or two welding. It only took about 20-25 minutes with this cold wire feed torch, so it does make a good contribution to bench work productivity, IMO.

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This photo of an outside weld that has already been inside "backwelded" by MIG shows an example of several items we've discussed and need to see to more fully understand.

#1 the tack is dressed in two planes of the sides of the tank. Since the tank was to be painted and the 'grinder scares' won't show, the size of the power tool 'tracks' was not kept as small as would be in a seam that would 'show'. The tracks are the two side panels' grinder marks, and good practice with a smaller wheel would be to keep them much smaller. Note the tack was hollow, so there was not need to cup the main body of the tack in order to minimize the final welds' bump or bulge at that tack.

#2 this is a good argument for outside welding first as a weld out sequence. There are several areas of the right hand sheet's edge that have been melted from the inside weld's fusion. That results in an uneven weld V to put the outside TIG bead into. Therefore, I do and may welders will, TIG outside welds first and then backweld inside with MIG so the inside fillet's weld mass fuses into the TIG welds' root. This still requires planning, dressing any TIG penetrations inside the tank (not always easy in the depth of a tank!) and it requires care with travel speed versus all up wattage of the welds inside to keep from collapsing the TIG bead's crown with 'suck back'.

#3 this weld seam has not be wire brushed prior to welding, the photo was to capture the tack, the edge collapse and show the heat effect of the inside weld.

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A photo of one of the two finished tanks prior to installation but painted with epoxy after, weld out, pressure testing and acid etching in prep for the paint systems.
There are plenty of fittings outside the tank to explore. First are the top fittings; (this is the port side tank) the centerline fitting to the right forward most corner is for the level sender and is raised up off the tank to allow the sending unit to register a little more 'top of tank' volume by raising the sender up 1". To the left of the tank's forward corner are the fill and vent fittings that will be connected to the port side or left of this photo. The fill is forward and 2" 1/2 fem coupler is recessed into a tank top doubler that allows the downcomer to resist vibrations and stiffen the top where a large hose will be fitted. Next aft on the left side of this tank is a 1" fitting for a vent - large vent as the dock fill rate of 2" requires more volume of flow off the tank top when filling at high rates of flow.

Aft and inboard (near right corner) on the top, is the draw fitting underneath is a 1/2" 6061-T6 pipe downcomer to connect to the filter draw side of the gas supply.

Now, the observant reader will notice there is a "the-Skipper-is-Always-Right-Fitting" on the bottom of the tank, that was installed because the Skipper is Always Right. This is a tank water bottoms drain fitting. I know that I've said the CG regs don't allow any tank fittings below the top but I have to let you know, who these tanks' owner is.

If you watch television then you may have seen the TV show "Deadliest Catch"? Well one of the boats in that show is owned by a family who has been fishing the Gulf of Alaska for a long time. These guys are called 'big-boat Skippers' in our neck of the woods, and they get a certain deference in the marine community. One of those families' patriarchs, whose family name and boat name would be recognized easily, asked me to do this project shown above. What do you do if; someone who has lived years at sea, run several of the boats that fish the Gulf for plural decades, and is still hiring boatwork done.... wanted a fuel tank bottom drain fitting(??) Any (local) welder would just ask "Where do you want that fitting, Sir?" That's what I did. [I doubt the local CG plans to do much inspecting of this man's play boat?] If anyone can tend a tank bottom drain; this man is can take care of a simple valve's operation!

There are various 'tapped blocks' welded to the tank's outer surfaces for different mounts, restraints/braces and we'll try to show how they worked in the final installations. Most are 1/2" 6061 plate cut and tapped to the size bolts they'll accept and they are TIGged 100% around their perimeters, then tank is pressure tested after all these welds are done, crater crack leaks can happen to any weld that is not tested, luckily I got by here- but outside wall welds require testing just as much as edge seams.

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This photo, above, of the SS, male thread body, vertical float acting, level sending units' top and bottom show why the sending unit top fittings were raised up off the tank surface.

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Second look at the fuel senders used in these tanks, notice the displays for the helm? When I powered up these two units I found I could get another 1-2" of the top of range if I slid the float all the way to the top limit of movement. That's why the fittings were raised up to allow the floats to move all the way to the top of the tanks and not be held down inside an inch or so by the top thread fitting. Not sure that the increased measurement is all that important but that's why the fittings were raised.

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Here is a pic of the SS fittings, all 316L except a few of the king nipples (hose barb to male NPT) which were only found in 304. This photo is before they were all deburred, and passivated prior to using on the boat. The top to StEl's are the fill hose connections, both run to port on this installation. Next are 1" combinations from hose to M;NPT for vents, below those vents, miniature versions of the same fittings for fuel draws. I might have gone with 2 back to back St. El's but the fuel filters were not located yet at this time so the draw lines were assumed to be horizontal at this location on top of tanks. Eventually these fuel draw lines were routed in the bilge so the 180 fittings would have been better choices.

The two pipe nipples and ball valves are for the water bottom drains, they were located in the bilge and had clean up sumps below them for any spillage that happened when drawing off water.

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This image of the industrial type full port ball valve shows a handle with a sliding lock and lock aperture in the handle and slide lock. (sliding handle lock 'fork' in previous photos as well) This valve can accommodate a pad lock or combo lock to trap the metal of the handle rotation lock and therefore only the Skipper could open and close these valves. While an extraordinarily experienced seaman - the proverbial 'old salt' - he was very willing to accept my suggestion of this "lockable" handle combination on his tank bottom drain valves so that no one but him could 'service' his tanks' water bottom draining!

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Last photo in this post, this picture was taken standing in the cabin, sole removed to show the tanks below, facing aft. The photo's right is port, and left is starboard; point of view is directly over the keel the two forward most fittings are the matching tank top mounted level senders. There is a collar tie between the two tanks, so there is not moment or leverage to allow these 600-700 lb. objects to even strain on their engine type mounts to the centerline stringer (between tanks) or the outboard stringers not shown here.

Next we'll look a bit closer as some mounting hardware, more of the plumbing and get a general feel for the overall installation of these two tanks in a fiberglass boat.

Cheers,
Kevin Morin
Kenai, AK
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Re: Metal Marine Tanks (mainly welded aluminum)

Post by mrintense » Tue Feb 16, 2016 6:49 am

I haven't posted a response in some time to this excellent posting Kevin, but I have been following it and I feel like I need to let you know that your effort is very much appreciated. The fact that you are willing to spend so much time to impart your knowledge and experience says volumes for your character. Thanks once again. I am sure that I and others will find this material very useful when the time comes to have our own tanks fabricated.
Carl
a.k.a. Clipper

Crafting a classically styled Vera Cruise named "Some Other Time"

Clipper's Vera Cruise Build

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Re: Metal Marine Tanks (mainly welded aluminum)

Post by tcough » Tue Feb 16, 2016 11:04 am

I'll second what Carl said.
Happy Boating,
Tracy

Building a 19'-9" Flats Flyer

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Re: Metal Marine Tanks (mainly welded aluminum)

Post by Kevin Morin » Tue Feb 16, 2016 5:48 pm

Thanks gentlemen for the kind words, and encouragement.
I'm sort of collecting many past articles here where builders may find them useful? One of my most frustrating memories was not being able to find this type of information in books, or anywhere in the 1970's when I was trying to get started doing this exact work.

What I hope is readers will be able to find at least a reliable starting point methodology to base their first few projects on so they can grow without the time lag of total trial and error learning !

thanks again, always willing to field any questions? I sometimes think that readers may believe that questions will be seen as some from of poor commentary on those who pose them? Nothing could be further from my attitude, the only poor question (often labeled dumb question by some posters; " I know this is a dumb question... but?" ) is one not asked. I didn't expect to post on and on... and on and on.... without anyone posting questions! Please post up, I'll try my best to see if there is an answer in my knowledge base, and I don't think it is 'dumb' if you don't know. Otherwise I was dumb for 30some years!

Cheers,
Kevin Morin
Kenai, AK
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Re: Metal Marine Tanks (mainly welded aluminum)

Post by Soloboat » Tue Feb 16, 2016 6:13 pm

This has been a learning experience I have only attempted to weld aluminum once it was such a frustrating experience that I never attempted again I am however following this thread with much interest and this makes me want to learn so I can use this knowledge. I farmed out my tank and had just a rectangular boxy job, if this info was available then I would have done the prep work at the very least and I would have had a tank that sat lower in the boat. Also this makes me want to revisit my tank to see if it was done properly by that I mean tank building for Marine app as outlined as shown QED.
cheers
keep it going I hope this gets archived
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Re: Metal Marine Tanks (mainly welded aluminum)

Post by Kevin Morin » Tue Feb 16, 2016 9:42 pm

Soloboat, learning to weld aluminum can be frustrating depending on your work experiences prior to trying. Also the instructive materials vary from full on classes to just a book with some descriptions. One of the best ways is to find someone close enough to drive to visit their shop, and see if you can make some financial arrangements with them to get started? Once you have some basics down, adding some welding equipment to your home shop and practicing is the remainder of the task. The basics for any given power supply, torch and process should be picked up in a few hours of practice under direct one-on-one supervision/instruction.

From then on, you just have to practice getting the muscles to do what your mind knows to do. Picking guitar, driving a car, welding are all related rate skills and they start with those first few steps; from then on its mainly repetitive practice.

Glad you like the thread, let me know if you have any specific questions that might help others if we discussed?

cheers,
Kevin Morin
Kenai, AK
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Re: Metal Marine Tanks (mainly welded aluminum)

Post by slug » Wed Feb 17, 2016 4:57 am

Kevin; Many thanks for all the time you're putting in to this comprehensive ""encyclopedia".
I have a 25 year old tank I was planning to "re-do" for my Gentry, but now have decided against that.

This brings up the following questions;

First, having gotten one very high (in my opinion of course) quote on building a simple box aluminum tank, I'm considering going at it myself' . I have considerable mig experience (have owned two mig welders... a 225 amp and now one of the smaller 180 amp Lincoln which I love) but have no aluminum welding experience. I have done quite a bit of stainless, both tig and mig.
, having done all my water tanks, railings, dodger, etc. on previous boats. The only aluminum experience was welding (gas) a damaged body for a dragster years ago, so I have some idea of the metal's "personality"
So, would I be better to go at a stainless tank that I would be reasonably comfortable welding, or should I try the aluminum with the push gun on the small mig machine?
I can get parts water jetted quite easily.
Just asking for advise, not a sealed contract. LOL

Thanks in advance; Doug
ps. Also hope Gayle will do something with your posts to make them readily available in the future. They are priceless.

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