I agree with JTMcC, but wish to add that (at least here north of 49) fill and cap procedures are usually location dependant. Outside the fence, downhill and xx10 is normal but inside the fence most work is uphill with xx18.
Outside the fence speed is king, and downhill allows the use of higher current and larger rods for high deposition rates. In addition, the pipe is normally buried which gives it added support and much more constant operating temperature. The consequence of failure can be lower.
Inside the fence the pipe is usually above ground and subject to much more variation in operating (and ambient)temperature and pressures. IIRC the codes are also different, and the consequence of failure can be higher.
For non code work such as water system piping, procedures are often not specified and the weldor can use their own discretion and experience. Small dia. propane and natural gas systems were commonly done with OA, but most are now plastic.
JMHE &.02