Explain this discrepancy of values used for HDPE in AutoPIPE compared to the Handbook of PE Pipe 2nd Edition?
The CAE development team did not make up these tables, Please see AutoPIPE's help for HDPE Reference Information, as one can see the tables were taken directly from the code books and relevant paragraphs. This would a question for the Code committee on why they choose these values over that in the handbook.
HDPE CC N-755-1 Piping Code Calculation Issues in AutoPIPE
Bentley AutoPIPE