What Went Wrong 2
Isolation Not Removed
While a plant was on line, an operator noticed a slip-plate on a tank vent. The slip plate had been fitted to isolate the tank from the blowdown system while the tank was under maintenance. When the maintenance was complete, the slip-plate was overlooked. Fortunately, the tank, an old one, was stronger than it needed to be for the duty. or it would have burst.
If a vessel has to be isolated from the vent or blowdown line, do not slip-plate it off, but whenever possible, disconnect it and leave the vessel vented to atmosphere (as shown in Figure 1-4).
If the vent line forms part of a blowdown system, it will have to be blanked to prevent air being sucked in. Make sure the blank is put on the flare side of the disconnection. not on the tank side (Figure 1-4).
Note that if the tank is to be entered. the joint nearest the tank should be broken. If a vent line has to be slip- plated because the line is too rigid to be moved, then the vents should be slip-plated last and de-slip-plated first. If all slip-plates inserted are listed on a register, they are less likely to be overlooked.