Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

PART TWO: FUEL SYSTEMS

TABLE 5-2. FUEL TANK MATERIALS AND THICKNESSES

Capacity Capacity Thickness Thickness

Material Specification Gallons Liters Millimeters Inches Gauge

Nickel-Copper ASTM-B127 1–30 1–112 0.78 0.0310 22 U.S. std.

(Monel) Class A 30–80 112–300 0.94 0.0370 20 U.S. std.

80–200 300–750 1.27 0.0500 18 U.S. std.

200–400 750–1,500 1.57 0.0620 16 U.S. std.

Copper-Nickel ASTM-B122 1–80 1–300 1.14 0.0450 17 AWG

200–400 750–1,500 1.83 0.0720 13 AWG

Copper ASTM-B152 1–80 1–300 1.45 0.0570 15 AWG

Type E.T.P. 80–150 300–560 2.03 0.0800 12 AWG

Copper-Silicon ASTM-B97 1–80 1–300 1.27 0.0500 16 AWG

Type AB&G 80–200 300–750 1.62 0.0640 14 AWG

200–400 750–1,500

Sheet Steel ASTM-A653/ 1–80 1–300 1.89 0.0747 14 MSG*

A653M-07

Stainless Steel 80–200 300–750 2.66 0.1046 12 MSG*

Aluminized Steel ASTM-463 1–80 1–300 1.89 0.0747 14 MSG*

80–200 300–750 2.66 0.1046 12 MSG*

Aluminum Alloy: 5052, 1–80 1–300 2.29 0.0900

5053, or 5086 50–80 190–300 2.54 0.1000

80–150 300–560 3.17 0.1250

150–300 560–1,100 4.83 0.1900

300–500 1,100–1,900 6.35 0.2500

*MSG= Manufacturer’s standard gauge for sheet steels.

NOTE: The thicknesses above occasionally need to be increased to achieve proper structural

strength.

Stainless Steel Tanks

Stainless steel has been used successfully for fuel tanks, but it was not recommended by ABYC

for many years. Dr. Harry Lipsitt, a professor of materials science, explains that it’s because of

corrosion at the welds, or “weld decay.” Most common marine-grade stainless steels, 304 or

18-8 (containing 0.08 percent carbon), contain both chromium and carbon. When the metal is

heated to over 1,000°F (538°C) for welding, the carbon is driven away and regions of

chromium carbide form, with chromium-depleted areas immediately adjacent. These two

“alloys” form a galvanic couple and can cause serious corrosion quickly.

The problem can be controlled by using a stainless steel with a strong carbide-forming

material: titanium. This is available as type 321 stainless. Another alternative is to use a low-

carbon alloy, with less than 0.03 percent carbon content. Type 316L or 317L meets this require-

ment. ABYC has recently accepted 316L and 317L tanks (for diesel) if welding is done accord-

ing to very rigid specifications (see ABYC H-33).