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TIG welding both sides of corner joint, legit?

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#21 · (Edited)
motolife313 said:
If you get full penetration from 1 side, I still don't see the need to try and weld on the back side. Pretty sure most pipe weldors only weld from 1 side
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Absolutely not the same thing. Aluminum is not receptive to open root welding in the way that steel is. It's not possible to get a full pen weld on aluminum that is quality unless you back gouge and then weld the other side. You're going to have a horrible mess if you try to weld it with a gap, and you're going to severely overheat the material if you try to get 100% penetration without a gap.

motolife313 said:
I could see it being stronger but that's a lot of extra welding.
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On a critical part like a fuel tank, you damn well better not be doing the bare minimum and assuming it's good enough. Products like that carry massive risk to the customer and massive liability to the manufacturer if it fails; only an idiot wouldn't overbuild it. To use your pipe welding example, that's why pipe is pressure tested at 150-200% of actual operating pressure. You simply cannot afford for it to fail. Simply "good enough" isn't good enough.

I can't speak to the regulations other industries have, but the Coast Guard requires fuel tanks be welded in that manner for any passenger vessel. It's probably a fair bet that there's good reason for it.
 
#22 ·
It looks like the Coasties are mostly concerned with tanks not leaking. Is there another reg covering fuel tank construction methods specifically?

33 CFR §183.510 Fuel tanks.

(a) Each fuel tank in a boat must have been tested by its manufacturer under §183.580 and not leak when subjected to the pressure marked on the tank label under §183.514(b)(5).

(b) Each fuel tank must not leak if subjected to the fire test under §183.590. Leakage is determined by the static pressure test under §183.580, except that the test pressure must be at least one-fourth PSIG.

(c) Each fuel tank of less than 25 gallons capacity must not leak if tested under §183.584.

(d) Each fuel tank with a capacity of 25 to 199 gallons must not leak if tested under §183.586.

(e) Each fuel tank of 200 gallons capacity or more must not leak if tested under §§183.586 and 183.588.


I bought three new/old stock tanks a few years ago for a scorching good deal. I used the 125-gallon one as the forward genset/day tank on my Chris Craft Roamer refit. The 68-gallon one I toss in my truck when I need to schlep diesel from the fuel depot to my home boiler tank or to fill the boat. The third one was odd-shaped and I was going to use it as auxiliary storage on the Roamer until we decided not to go the slow trawler route and repowered with twin 450hp Cummins diamonds. I had to cut the tank to get it out of the boat, and I've been slowly cutting it apart as practice coupons as I learn TIG. Here are some shots of the outside and inside. This is a commercially built tank, made by Florida Marine Tanks, which is an OEM supplier to a bunch of reputable boat manufacturers.

Outside corner

Inside corner

Note how penetration changes from the left side to the right.
 
#23 ·
Hillbilly Welder said:
Absolutely not the same thing. Aluminum is not receptive to open root welding in the way that steel is. It's not possible to get a full pen weld on aluminum that is quality unless you back gouge and then weld the other side. You're going to have a horrible mess if you try to weld it with a gap, and you're going to severely overheat the material if you try to get 100% penetration without a gap.



On a critical part like a fuel tank, you damn well better not be doing the bare minimum and assuming it's good enough. Products like that carry massive risk to the customer and massive liability to the manufacturer if it fails; only an idiot wouldn't overbuild it. To use your pipe welding example, that's why pipe is pressure tested at 150-200% of actual operating pressure. You simply cannot afford for it to fail. Simply "good enough" isn't good enough.

I can't speak to the regulations other industries have, but the Coast Guard requires fuel tanks be welded in that manner for any passenger vessel. It's probably a fair bet that there's good reason for it.
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AWS D1.2, and D17.1 say otherwise. Besides open corner joints and open root joints are 2 different beasts. Plenty people myself included can tig weld a full penetration single weld groove, or corner joint that can pass radiography, bend, reduced tensile, and macro examination. A proper qualified procedure can produce quality welds in this manner.

Are you talking about GMAW alum welds? I agree with you then.
 
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#24 ·
I don't know anything about that Florida company or who they supply boats for, but my guess is that most of them aren't going in to commercial (carrying passengers for profit) vessels, as I specified above.

The ABYC standards for fuel tank construction exceed the Coast Guard requirements, and they want to see the tanks welded inside and out.

I'm not privy to the design process of our boats; what I do know is that for passenger vessels, the Coast Guard wants to see the fuel tanks at least twice. Before the lid is welded, and during the pressure test. We build all of our tanks, Coast Guard inspected or not, in this way, because it is the best, most reliable method of construction. Lots of people, unfortunately, think it's okay to just do the bare minimum to make a part work. When it's a critical part like this, that is an irresponsible way to go about things. It looks to me like Florida Marine Tanks might be one of those "bare minimum" type of manufacturers.

After seeing how tanks of lesser quality can fail, I will never use one in my boats that I don't know to be over-built.
 
#25 ·
I'm pretty sure the OP isn't making a tank for commercial/USCG inspected vessel.

That said, ABYC H-33.s doesn't stipulate inside and outside welds for diesel fuel tanks. The only requirements for welds are that they pass the specified leak tests (same as 33CFR) and that, if aluminum, the alloy must be 5052, 5083, or 5086 using Inert Gas Shielded Arc Resistance process (presumably that's MIG or TIG, but is spray transfer "resistance" welding per se?).

The only part of H-33.S where I could see somebody believing there's an implied need for double-sided welding would be in REQUIREMENTS IN GENERAL, specifically the last one, e:
In order to attain the highest practical degree of freedom from fuel or vapor leakage within the hull, all parts of the system shall comply with the following:
a. All component parts of the fuel system shall comply with the applicable sections of this standard and shall be so documented.
b. The entire system shall be liquid and vapor tight to the hull interior.
c. The system shall be permanently installed and all component parts shall be independently supported.
d. All components of the system shall be accessible (see ABYC H-33.7.d.).
EXCEPTION: Fuel tanks.
e. Individual components of the system, and the system as a whole, shall be designed to withstand the combined conditions of pressure, vibration, shock, and movement encountered under normal operating conditions.

So if, under normal operating conditions your boats need tanks welded inside and out, that's that. But it doesn't mean that everybody with a day cruiser or fishing boat needs it.
 
#26 ·
shovelon said:
AWS D1.2, and D17.1 say otherwise. Besides open corner joints and open root joints are 2 different beasts. Plenty people myself included can tig weld a full penetration single weld groove, or corner joint that can pass radiography, bend, reduced tensile, and macro examination. A proper qualified procedure can produce quality welds in this manner.

Are you talking about GMAW alum welds? I agree with you then.
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AWS D17.1 also mandates an argon purge be used during the test. Easy to do on a test plate, much harder to do on a fuel tank. The issue with trying to weld an open root with aluminum is the same issue you face with stainless; there is no protection on the back side of the root against the atmosphere. Not to mention, aluminum has the added issue of the backside not being subject to the cathodic bombardment that removes the oxides from the face of the weld, so those oxides contaminate the weld from the back side.

I'm not trying to suggest that a quality tank CAN'T be built by just TIG welding the outside, and not welding the inside. It most certainly can.
 
#27 ·
q240z said:
I'm pretty sure the OP isn't making a tank for commercial/USCG inspected vessel.
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I'm quite certain that he isn't. I was simply using the USCG standards as an illustration of what is a "good idea". The USCG doesn't care if you go out in a bathtub, as long as it's a personal vessel. That doesn't make it a good idea.

That said, ABYC H-33.s doesn't stipulate inside and outside welds for diesel fuel tanks. The only requirements for welds are that they pass the specified leak tests (same as 33CFR) and that, if aluminum, the alloy must be 5052, 5083, or 5086 using Inert Gas Shielded Arc Resistance process (presumably that's MIG or TIG, but is spray transfer "resistance" welding per se?).

The only part of H-33.S where I could see somebody believing there's an implied need for double-sided welding would be in REQUIREMENTS IN GENERAL, specifically the last one, e:
In order to attain the highest practical degree of freedom from fuel or vapor leakage within the hull, all parts of the system shall comply with the following:
a. All component parts of the fuel system shall comply with the applicable sections of this standard and shall be so documented.
b. The entire system shall be liquid and vapor tight to the hull interior.
c. The system shall be permanently installed and all component parts shall be independently supported.
d. All components of the system shall be accessible (see ABYC H-33.7.d.).
EXCEPTION: Fuel tanks.
e. Individual components of the system, and the system as a whole, shall be designed to withstand the combined conditions of pressure, vibration, shock, and movement encountered under normal operating conditions.

So if, under normal operating conditions your boats need tanks welded inside and out, that's that. But it doesn't mean that everybody with a day cruiser or fishing boat needs it.
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The USCG only requires 1/4PSIG for the pressure test, while the ABYC, if memory serves, states 3. Quite a difference. Certainly enough to make obvious some leaks that might otherwise go undetected.

At the end of the day, you can build your fuel tanks however you want. It makes not an ounce of difference to me. But, I've personally seen what can happen when those fuel tanks fail. It's not pretty. And as a result, I am firmly of the belief that fuel tanks, like oil and gas lines, are NOT something to build to "good enough" standards.
 
#29 ·
motolife313 said:
Come on, good enough means it will last forever
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Sarcasm, or stupidity? Not sure.

Would you be okay with a high pressure steam line with an operating pressure of 8000 PSI be pressure tested at 8002 PSI? After all, that's "good enough," right?

Hell no. There is a REASON that those lines are overbuilt. There is a REASON that they're tested to 12,000 PSI when their operating pressure is in the 6-8000 range. They're built to withstand considerably more than what is "normal" in their operating parameters, and fuel tanks should be treated the same way.
 
#31 ·
Hillbilly Welder said:
AWS D17.1 also mandates an argon purge be used during the test. Easy to do on a test plate, much harder to do on a fuel tank. The issue with trying to weld an open root with aluminum is the same issue you face with stainless; there is no protection on the back side of the root against the atmosphere. Not to mention, aluminum has the added issue of the backside not being subject to the cathodic bombardment that removes the oxides from the face of the weld, so those oxides contaminate the weld from the back side.

I'm not trying to suggest that a quality tank CAN'T be built by just TIG welding the outside, and not welding the inside. It most certainly can.
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Alum does not degrade due to atmospheric exposure during welding. It immediately forms a protective oxide layer and does not migrate degradation subsurface.

I have never seen where D17.1 or D1.2 specifies purge on alum. But many AWS SWPS may specify purge or not. The only SWPS available from AWS for alum which I have is for 5052 and does not require purge. None of my qualified PQRs have included purge on alum and have been approved by Boeing, Litton, Raytheon, General Dynamics, Hughes Research, and others.

Do you have a revision, section, and paragraph citing the purge requirement for alum full pen welds?
 
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#32 ·
These reduced section tensile coupons welded with 4043 on 6061 and not backpurged broke outside of the weld nugget and exceeded minimum PSI to qualify procedure. Which also qualifies open corner outside fillet welds. Perhaps NavSea requirements are different.

Image


Same with these root and face bends.
Image


Here is the macro.
Image
 
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#33 ·
Let’s get something straight right off the bat! I’m no Tig welder by any stretch of the imagination!:eek::eek:
Several years ago I built a 60-gallon aluminum farm gas tank. I Tig welded inside and out. Except the top, it was only welded on the outside. I tested it with 4-PSI of air. I got a few bubbles in the Top welds!:eek:
 

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#34 ·
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#35 ·
CEP said:
Let’s get something straight right off the bat! I’m no Tig welder by any stretch of the imagination!:eek::eek:
Several years ago I built a 60-gallon aluminum farm gas tank. I Tig welded inside and out. Except the top, it was only welded on the outside. I tested it with 4-PSI of air. I got a few bubbles in the Top welds!:eek:
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Were they leaking through the craters?
 
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#37 ·
Hillbilly Welder said:
I'm quite certain that he isn't. I was simply using the USCG standards as an illustration of what is a "good idea". The USCG doesn't care if you go out in a bathtub, as long as it's a personal vessel. That doesn't make it a good idea.

At the end of the day, you can build your fuel tanks however you want. It makes not an ounce of difference to me. But, I've personally seen what can happen when those fuel tanks fail. It's not pretty. And as a result, I am firmly of the belief that fuel tanks, like oil and gas lines, are NOT something to build to "good enough" standards.
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The "USCG standards" you mentioned don't seem to exist, though. I linked to and copied the actual Coastie reg and ABYC standards, neither one of which requires inside welds. I'm not saying overbuilding is necessarily a bad idea, but you've been calling out uncited regulations and standards that are at odds with the actual published ones. To my way of thinking, building to the established standard isn't "good enough," which makes it sound like baling wire, bubble gum, and some of that fancy aluminum HVAC tape are holding it together.

That said, the only failed aluminum tanks I've seen have been corroded ones from installations that permitted water to collect on the underside between the tank and its supports. Not even double-sided welds would fix that. Could be in commercial service, where the tanks are thousands or tens of thousands of gallons, the stresses on the welds warrants the extra effort. The OP's tank didn't look like it was all that big.

Either way, it's an interesting discussion.
 
#40 ·
q240z said:
The "USCG standards" you mentioned don't seem to exist, though. I linked to and copied the actual Coastie reg and ABYC standards, neither one of which requires inside welds. I'm not saying overbuilding is necessarily a bad idea, but you've been calling out uncited regulations and standards that are at odds with the actual published ones. To my way of thinking, building to the established standard isn't "good enough," which makes it sound like baling wire, bubble gum, and some of that fancy aluminum HVAC tape are holding it together.

That said, the only failed aluminum tanks I've seen have been corroded ones from installations that permitted water to collect on the underside between the tank and its supports. Not even double-sided welds would fix that. Could be in commercial service, where the tanks are thousands or tens of thousands of gallons, the stresses on the welds warrants the extra effort. The OP's tank didn't look like it was all that big.

Either way, it's an interesting discussion.
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They exist somewhere; I don't know where. I'm not the engineer, but I build the tanks, and the boats that go in them, for a living. I stand there and witness the USCG inspections. I don't know where the standards came from, if it's simply a requirement because it was designed that way or there's some broader regulation, but the USCG wants to look inside our fuel tanks to ensure that they're being constructed properly.

And even if they didn't, I'm still firmly of the belief that it's the proper way to build them. I say that not simply because of the theory that a weld on both sides is better than a weld on one side, but because I have actually seen with my own eyes what can happen when a fuel tank develops a leak. It's a miracle that it happened in a harbor, with nobody on board but the captain, and he walked away uninjured. If it had happened at sea, with a full load of paying customers, that would have been catastrophic. Even if nobody has any published regulations dictating it, which I really don't know, it's still the right way to do it. With critical parts like that, with the potential to cause massive financial and bodily harm if they fail, it is a fool's errand to settle for "good enough".
 
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