Preffered joint for aluminum?

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Hello there.I've got a fellow who wants me to build him a couple of aluminum fuel tanks, for the back of his 1 tons for fueling equipment.  I don't have alot of expierience with aluminum, so i started looking at the welds on the deck of my rig, and on my auxillary diesel tank, both are aluminum.  It looks like the outfit I got to build them, put a bend at most seams, so that they would have as many lap joints as possible.  As opposed to corner joints.I can see that it would be harder to blow through a lap joint as opposed to a corner joint, but is it any stronger? I have built several steel tanks, and always used open corner joints, any help will be greatly appreciated.Regards,Donkey.
Reply:I can see that it would be harder to blow through a lap joint as opposed to a corner joint, but is it any stronger?Corner joints in AL, can easily have less that complete fusion...but "they look great",and for amatuer tank builders--it's the looks that count.The inside of a corner weld, especially in AL can and do exhibit defects in the weld bead center,which easily creates cracking.Corner welded tanks having internal baffle plates either tacked or lightly welded can easilysuffer permanent deformation during a too aggressive pressure test, done by those whohave no clue on pressure testing.Lapped/flanged heads, fully lapped/flanged baffles and a lapped tank body construction are orders higher in impact/crash resistance and fatigue strength. Tanks constructed like this can pass DOT impact testing, etc. Witness the construction of Transfer Flow tanks. (I used to be a dealer forthem and learned from their robust design and fab methods.)There's a bunch of ways to define 'strong'. AL tanks can fatigue crack, big time-fast.Nurse tanks in the back of a pickup get the hell knocked out of them. Bed flexing can rip a tank--if it's mounted without any give.For heavy use, off road nurse tanks, I've created a center point rest/mount (directly under a flanged baffle), then allow for the tankto teeter-tooter, slightly, via elastomeric outer corner mounts that had give,due to bed flexing. Beds flex much more than folks would think.Hope this helps. The costs of doing it the right way versus the 'pretty' way,are around 3X--which actually is cheap, if one bothers to consider just'what?' a cracked, leaked-out tank can cost.Blackbird