(b) Where the hoop stress corresponding to the established maximum allowable operating pressure of a segment of pipeline is not commensurate with the present class location, and the segment is in satisfactory physical condition, the maximum allowable operating pressure of that segment of pipeline must be confirmed or revised.

1. (1) If the segment involved has been previously tested in place to at least 90 percent of its SMYS for a period of not less than eight hours, the maximum allowable operating pressure must be confirmed or reduced so that the corresponding hoop stress will not exceed 72 percent of SMYS in Class 2 locations, 60 percent of SMYS in Class 3 locations, or 50 percent of SMYS in Class 4 locations.
2. (2) If the segment involved has not been previously tested in place as described in paragraph (1) of this subdivision, the maximum allowable operating pressure must be reduced so that the corresponding hoop stress is not more than that allowed by this Part for new segments of pipelines in the existing class location.

3. (3) If the segment of pipeline involved has not been qualified for operation under paragraph (1) or (2) of this subdivision, it must be tested in accordance with the applicable requirements of this Part, and its maximum allowable operating pressure must then be established so as to be equal to or less than each of the following:

   1. (i) The maximum allowable operating pressure after the requalification test is 0.8 times the test pressure for Class 2 locations, 0.667 times the test pressure for Class 3 locations, and 0.555 times the test pressure for Class 4 locations.
   2. (ii) The maximum allowable operating pressure confirmed or revised in accordance with the section, may not exceed the maximum allowable operating pressure established before the confirmation or revision.
   3. (iii) The corresponding hoop stress may not exceed 72 percent of SMYS in Class 2 locations, 60 percent of SMYS in Class 3 locations, or 50 percent of SMYS in class 4 locations.