The tank, located in a cold area of the mill, had dripped water onto the floor which eventually froze to create a slip hazard. Maintenance personnel locked out the power to the electric pump, drained the tank, disconnected the piping, and removed the bolts holding the tank to a concrete pad.
When they tipped the tank onto its end, the pump appeared loose, so they checked its gasket and reseated it. Then they rebolted the tank to the pad, reconnected the piping, and opened the inlet and discharge valves each a quarter turn to allow condensate back into the tank.
The drip began again almost immediately. One worker knelt down to visually locate the leak. Moments later a burst of steam escaped and the bottom of the tank blew off. Steam and hot condensate gave the worker and four others second-degree burns.
The square, cast-iron condensate tank was not intended to be a pressure vessel. When the inlet valve was open, pressure built to an unsafe level and caused the rupture. Opening the valve on the discharge pipe did not help relieve the pressure because the pump that fed the discharge pipe was still off.
A warning label near the inlet fitting said as much and indicated the tank had to be vented at all times. But the label was covered with dirt, and workers said they were unaware of the need for a vent. Indeed, a vent at the top of the tank had been capped off.
A construction company had installed the tank, working from drawings that did not show a vent line or specify the need to vent the tank to the outdoors. The tank manufacturer said the vent line had been mistakenly omitted from the drawings.
The installers admitted they would not have drawn attention to the need for an external vent line if one wasn’t specified because that would have exceeded the scope of their work. They may have capped the vent, or a mill worker may have capped it later to prevent vent steam from escaping into the work area.
After the accident, the mill replaced the ruptured condensate tank with an ASME-approved pressure-vessel system with pressure gages, relief valves, and lockout-ready power sources. Management also reviewed lockout procedures throughout the plant because the inlet pipe delivering hot condensate to the tank should have been considered an energy source and properly locked out before the workers started their maintenance.
This month’s safety violation comes from the files of Lanny Berke, a registered professional engineer and Certified Safety Professional involved in forensic engineering since 1972.
Edited by Jessica Shapiro