PE pipe maintains a of 155–165 over 50+ years — much better than steel or concrete.
While you may find "previews" or older snippets for free, the official second edition (2020) is a paid resource. Below is a guide on where to find the official manual, how to access it through legitimate channels, and what to expect in the latest version. Official Paid Access (PDF & Hardcopy)
While the search term "AWWA M55 PDF free download" is popular, it comes with significant downsides: