Code L10DH:

L = Type of tank:

Tank for substances in the liquid state (liquids or solids handed over for carriage in the molten state).
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10 = Calculation pressure:

Minimum calculation pressure: 10 bar (see 6.8.2.1.14)
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D = Openings (see 6.8.2.2.2):

Tank with top-filling and discharge openings with no openings below the surface of the liquid.
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H = Safety valves/devices:

Hermetically closed tank (see 1.2.1).