49 CFR §195.424

1. (a)No operator may move any line pipe, unless the pressure in the line section involved is reduced to not more than 50 percent of the maximum operating pressure.
2. (b)No operator may move any pipeline containing highly volatile liquids where materials in the line section involved are joined by welding unless—
   1. (1)Movement when the pipeline does not contain highly volatile liquids is impractical;
   2. (2)The procedures of the operator under § 195.402 contain precautions to protect the public against the hazard in moving pipelines containing highly volatile liquids, including the use of warnings, where necessary, to evacuate the area close to the pipeline; and
   3. (3)The pressure in that line section is reduced to the lower of the following:
      1. (i)Fifty percent or less of the maximum operating pressure; or
      2. (ii)The lowest practical level that will maintain the highly volatile liquid in a liquid state with continuous flow, but not less than 50 p.s.i. (345 kPa) gage above the vapor pressure of the commodity.
3. (c)No operator may move any pipeline containing highly volatile liquids where materials in the line section involved are not joined by welding unless—
   1. (1)The operator complies with paragraphs (b) (1) and (2) of this section; and
   2. (2)That line section is isolated to prevent the flow of highly volatile liquid.