[2.0.20](build 80511 expansion, win64)
base 2.0.20
elevated-rails 2.0.20
quality 2.0.20
space-age 2.0.20
wrong pipe, Pipeline contents water, but there must be Heavy oil.
Welcome to the forum, and thank you for the report.
I loaded the save, undid & redid some actions and I believe this is the one that started it all:
Vulcanus-WaterInPipe.jpg (90.41 KiB) Viewed 208 times
Water got into the pipe connected to oil refinery's heavy oil output and even though chemical plants were removed and placed again, this one pipe was never removed, always contained water and kept contaminating pipes meant for heavy oil.
The easiest fix is to click on the pipe, then "Flush Water from this pipeline".