$B2$ and $C2$ stress indices are needed for evaluation of nuclear piping components. These indices are used in calculation of stress terms corresponding to moment loading. The formulas $(B2=1.3/h2/3$ and $C2=1.95/h2/3)$ given in the ASME Boiler and Pressure Vessel Code for calculating these stress indices for elbows and bends are independent of bend angle. Author’s earlier work indicated that the values obtained by these formulas are conservative for bend angle ⩽90 deg. The objective of the present study was to investigate the values of $B2$ and $C2$ stress indices for elbows with bend angles larger than 90 deg and to evaluate the limit of the applicability of the ASME Code formulas in terms of the bend angle. For this purpose, elbows with bend angles ranging from 90 to 180 deg have been investigated in detail. Elbow sizes studied ranged from 2.5 to 20 NPS. Finite element models have been used for detailed analysis. To cover the worst case of stresses in the elbows, several hundred load cases were analyzed by varying the direction of the moment loading. It was found that the three independent loading cases corresponding to three orthogonal axes do not bound the worst-case stress in the elbows. The results of the analysis show that the calculated value of $B2$ stress index increases with bend angle; but its value, even for 180-deg bend angle, remains below the ASME Code value with a margin of at least 15%. Considering all analyzed elbows and bend angles from 90 to 180 deg, the calculated maximum value of $C2$ stress index is found to be within 2 percent of the ASME Code value. The maximum increase in the value of $B2$ stress index is 12.5 percent as the bend angle is increased from 90 to 180 deg. The corresponding increase in the $C2$ stress index is less than 8%. Based on these results and authors’ earlier work, a modification to ASME Code formulas is proposed for calculation of more realistic values of the stress indices for bends up to 180 deg.

1.
ASME Boiler and Pressure Vessel Code, Section III, Div. 1, 1998 Edition.
2.
ASME Boiler and Pressure Vessel Code Case N-319-2, 1990, “Alternate Procedure for Evaluation of Stresses in Butt Welding Elbows in Class 1 Piping, Section III, Division 1.”
3.
Kumar
,
R.
, and
Saleem
,
M. A.
,
2001
, “
Bend Angle Effect on B2 and C2 Stress Indices for Pining Elbows
,”
ASME J. Pressure Vessel Technol.
,
123
,
May
, pp.
226
231
; also, presented at the ASME/PVP Conference, Seattle, WA, July 23–27, 2000.
4.
Liu, T., Kumar, R., Saleem M. A., and Usmani, S. A., 1998, “Stress Indices for Feeder Pipe Bends Based on Finite Element Analysis,” ASME PVP-Vol. 388.
5.
ANSYS, Version 5.3, “Finite Element Program,” Swanson Systems Inc., Houston, PA.
6.
Yu, L., and Matzen, V. C., 1998, “B2 Stress Index for Elbow Analysis,” Proc., 7th Int. Symp. on Current Issues Related to Nuclear Power Plant Structure, Equipment and Pip. Held at North Carolina State University, Raleigh, NC.
7.
Williams, D. K., and Lewis, G. D., 1984, “Development of Primary and Secondary Moment Loading Stress Indices for Trunnion Elbows,” ASME PVP-Vol. 98.