Tower internals manways

Contract maintenance workers often will not replace the tray manways unless the tray manway is adjacent to a tower external manway. They reason that once the tray manways that are visible from the tower manway are closed, there is no way for someone to inspect the other trays. This problem is not just common— it is imiversal. The maintenance force at the Good Hope Refinery pulled this nasty trick on me at the coker fractionator. Equipped with my crescent wrench, I opened the tray internal manway below the side tower manway. 1 discovered that the 12 trays below this point had their manways stacked in their downcomers. In 1990,1 worked on a project to improve fractionation at the Chevron Refinery crude distillation unit in El Segundo, California. When the tower was opened to implement my design, the tray manways were found lying on the tray decks below the diesel draw tray. The lesson is, inspect each tray and then witness the closure of each tray manway, separately. 

The situation on a trayed tower is far more controllable. Even after the tray assembly is complete, the process engineer, using only a crescent wrench, can open a few tray deck manways and doublecheck the tower internals. But to pull 6 ft of packing out of a tower is a major undertaking. Also, trays can be stepped on without damage. Beam supports and 40-lb air guns can be dragged across a sieve tray... 

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