At the present time, rules for design of piping for nuclear power plant elevated temperature service are contained in Code Case 1592-8. A Task Group under the Code Working Group on Pipe Design has prepared a revised portion on piping for a future revision of Code Case 1592. This revised portion contains explicit equations for calculating stresses; those stresses are limited by the general stress limits of the Code Case. The stress equations involve the use of stress indices which, except for the B/sub 2/' indices, are given in the present Code, NB-3600. This report started as an effort to develop appropriate B/sub 2/' indices for inclusion on the Code Case. However, the report shows that the B/sub 1/ and B/sub 2/ indices are based on limit load concepts hence there is no need for the B/sub 2/' indices. The general concepts and motivation behind the stress index approach is described. The background of the B/sub 1/ and B/sub 2/ indices is given for the several types of piping products covered by the indices. This report is concerned with stress indices in equations as used for checking the equivalent of ''Primary Stress Intensity Limits.'' It does not address the use …