(a) Except as provided in subdivision (c) of this section, no person may operate a segment of steel or plastic pipeline at a pressure that exceeds the lowest of the following:

1. (1) the design pressure of the weakest element in the segment, determined in accordance with this Part;

2. (2) the pressure obtained by dividing the pressure to which the segment was tested after construction as follows:

   1. (i) for plastic pipe in all locations, the test pressure is divided by a factor of 1.5;

   2. (ii) for steel pipe operated at 100 psig (689 kPa) or more, the test pressure is divided by a factor determined in accordance with the following table:

      Factors
      Class Location	Installed before (Nov. 12, 1970)	Installed after (Nov. 11, 1970)	Converted under § 255.14
      1	1.1	1.1		1.25
      2	1.25	1.25		1.25
      3	1.4	1.5		1.5
      4	1.4	1.5		1.5

3. (3) the highest actual operating pressure to which the segment was subjected during the five years preceding July 1, 1970, unless the segment was tested in accordance with section 255.505 or 255.507 of this Part during the five-year period or the segment was upgraded in accordance with section 255.555 or 255.557 of this Part. The MAOP must not exceed the MAOP on August 30, 2011 if the MAOP is determined using this method.
4. (4) for furnace butt welded steel pipe, a pressure equal to 60 percent of the mill test pressure to which the pipe was subjected;
5. (5) for steel pipe other than furnace butt welded pipe, a pressure equal to 85 percent of the highest test pressure to which the pipe has been subjected, whether by mill test or by post installation test; or
6. (6) the pressure determined by the operator to be the maximum safe pressure after considering the history of the segment, particularly known corrosion and the actual operating pressure.