Answer: 

As of AutoPIPE Vesel version 46, Distributed loads are applicable only to vessels and not to storage tanks. This limitation arises from the vessel type configuration—vessels are modeled as beams to facilitate the application of external loads, whereas tanks are not.

For tanks, only point loads are considered, and these are applied to the bottom, wall, and/or roof depending on their location.
We will update the help documentation to include these details for future reference.

Should you consider this feature a valuable addition to AutoPIPE, kindly examine the existing IDEAs available here and cast your vote for the one you support. If the IDEA has not yet been submitted, please feel free to post a new idea. These IDEAs and all comments are forwarded directly to the development team and the Program Manager for their evaluation and feedback.