See my post in the waste heat steam generator thread. It’s in the process of being a bad day as we have yet to figure out what we are doing wrong.
The other bad day I had was when the sulfur pit overflowed on start up after a TA because both sulfur pumps were found locked up with corrosion products/sulfurcrete.
Smaller bad days were due to lean amine leaks caused by extreme localized corrosion of the heat affected zone of butt welds in hot lean amine piping. 360 degree corrosion of the HAZ was found, almost like it was machined.
Also have had unplanned shutdowns due to knocking the trays out of one side of the amine regenerator tower. Tracer scan on one side looked liked the tower was fine. Opened up the tower and could look from the top to bottom on the other side of the tower. Lesson- scan both sides of the tower when you have split trays.
Lean/Rich Amine exchanger fouling also caused an unplanned shutdown (in January in Minnesota, naturally). Fouling composition was mostly iron, sulfur, silica, and alumina/aluminum. Still not sure where it all came from.
Life is good. There’s no end of lessons to learn in the yellow cokers!