High pressure inside pipe will try to elongate pipe resulting in axial stresses. In case you are having elbow at pipe ends, pressure will stiffen the pipe bends resisting bend ovalization. This happens due to the pressure difference between pipe and atmosphere, typically known as Bourdon effect.
Pressure can affect the large diameter pipes having high D/t ratio. This is addressed in B31.3 Appendix D (Table D300 Note 7)
You can also refer peng paper on pressure elongation. Also, use search option.