There is an Australian standard “AS1020 (1984) – Control of undesirable Static Electricity” In it, there is a table for flammable hydrocarbons as follows:
Pipe Size (mm) Max Velocity (m/s)
10 8
25 4.9
50 3.5
100 2.5
200 1.8
400 1.3
600+ 1.0
This is based on pure hydrocarbons, and there is a correction, which can be applied for fluids of different conductivity. Methanol has a higher polarity than hydrocarbons and hence is more conductive. The resistivity of diesel is 1013 ohm-m vs 108 for methanol. In addition to this, normal piping design guidelines should however be followed, such as appropriate earthing, and ensuring exit velocities into tanks of 1 m/s.