welds are subject to damage and corrosion.
(One-quarter inch and thicker—the next stan-
dard size up after 0. 190 inch, 4.82 mm—can’t
be bent to small radii and is thick enough to
weld more effectively.) Sheet-metal tank walls
should be wrapped around corners in a ra-
dius, with longitudinal butt-weld seams well
away from the corners (Figure 5-14). On
smaller, regularly shaped tanks, a single sheet
can be wrapped all around and closed with
just one longitudinal weld. Larger tanks or
tanks with complex shapes must be made up
of several wall sections requiring more than
one seam. The tank’s ends should be formed
of flat plate or sheet with the edges bent in-
ward to form a flange all around its perimeter.
These bends should be radiused, and the tank
walls should be welded to the flanges—not on
the corners, but approximately^3 / 16 inch
(4.7 mm) in from the edge.
This construction is termed lapped-corner
construction (sometimes flanged-corner
construction). Though it is superior for metal
tanks of small to medium size (it can’t be
used on plate over^3 / 16 inch [4.7 mm] thick,
because the thick plates won’t take the
bend), it is not acceptable under the CFR for
commercial vessels. The reason for this is
unclear. It may stem from the incorrect prac-
tice of fabricating with lapped externalcor-
ners that could trap water (particularly on
the top of the tank) leading to corrosion.
Regardless, this is the regulation, and lapped-
corner construction cannot be used on Coast
Guard–inspected passenger vessels.Tank Labels
Locating a tank’s manufacturer shouldn’t be
difficult. The CFR and ABYC require that all
tanks be labeled (Figure 5-15) with the- manufacturer’s name and address
- date of manufacture
Chapter 5: Fuel Tanks and Fittings
Figure 5-14.
Radius corner
tank construction