Need more info to help you.  Is this a small generator set with rubber mount? (Threaded pipe with flex hose to engine’s fuel filter).   It is best to follow the manufacture’s recommendations.  Get the generators installation manual and follow there recommendations.

Do not use any galvanized pipe.  Zinc will leach into the fuel and cause injector problems.

Also be sure to check out the fire protection codes

Patricia Lougheed

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The generator manufacturer advises using "black iron pipe" through out the diesel fuel system.  I have been informed to definitely keep away from galvanized and copper conduit.

What is "black iron pipe?" and what protection does it need if it is going to be buried in the ground?  Can "black iron pipe" be purchased with an anti-corrosion coating?

Thanks,

No such thing as "black iron pipe". There used to be wrought iron pipe, but it hasn't been manufacturered or available in several decades. They likely mean carbon steel pipe, like A53F (very often junk - I'd avoid it), A53B ERW, or A106B seamless.

Check the code requirements for fuels in your area. If you're going to bury a fuel line, I'd bet you have to meet the same standard as the gas station operators.

in addition to that line,it will be better to provide a level controller or indicator.

1) In the field, black iron pipe commonly refers to carbon steel pipe such as A53, A106, A120 etc. without a galvanized, painted, or tape coating.
2)  Typically it is socket welded sch 80 for 2 inch and smaller.  Hook ups to the generator should be an approved flexible hose, as opposed to hard piped.
3)  Buried fuel piping is typically installed in double containment piping.  The project I did used 1 inch carbon steel piping contained inside a 3 inch fiberglass containment piping system.  

Onan/Cummins (Emergency Generator) Application manual requires black steel pipe for diesel fuel lines - Do not use galvanized fuel lines, fittings or tanks. Condensation in the tank and lines combine with sulfur in the fuel to produce sulfuric acid. The sulfuric acid reacts with zinc in the galvanized coating and contaminates the fuel. Do not use copper tubing for diesel fuel lines. Diesel fuel polymerizes (thickens) in copper tubing during long periods of standby and will clog the fuel injectors. Use a flexible section of tubing (code approved) between the engine and fuel supply line to withstand generator set vibration. The manual shows figures (12 & 13) for day tank piping depending on if main supply tank is below or above the generator. So get the application manual.