Why is it not possible to use elbows with HDPE pipe as with steel pipe?
(Note from AutoPIPE Help: "For HDPE pipes, only Close and Wide are accepted options.")
At this time, AutoPIPE has only provided HDPE for B31.1 and ASME NC/ND and that uses the CC-N755-1 provisions. CC-N755-1 only permits miter bends for HDPE and provides B1 & B2 indices for miter and close bends only.
Otherwise, you would need to have stress indices for your HDPE bends that could be manually entered.
Model Non-metallic properties