A ruptured steam pipe was the catalyst for the collapse of a storage tank January 16 at the Vopak Botlek TTR terminal in the Netherlands, according to Vopak information. The company reported 421 people presented complaints at an emergency room after the incident.
The ruptured pipe produced pressure waves, that in conjunction with a failure of a wall weld, resulted in the release of 1,700 metric tons of orthocresol.
The chemical is used in cresol-formaldehyde resol and xpoy-cresol novalc resins, as well as a polymerization inhibitor. It also is used in some products for janitorial supplies, according to information from the American Plastics Council.
Vopak said the Netherlands incident occurred as product was unloaded from a ship into the steam-heated tank. The rupture at the tank's weld spread out and down at a fast rate, resulting in the product spilling out of the tank with such force that it was carried over the tank pit compound wall, Vopak said.
The tank then lost stability and collapsed, shearing the connection between the tank wall and the tank bottom in the process. When the tank collapsed, it severed the tank roof from the tank cylinder, and the tank roof drifted away from the tank and onto the released product.
Shipping on the waterway where the incident occurred, and train services between Rotterdam and the Hook of Holland, were temporarily suspended. Cleanup took five months.
The steam heating coil, with a total length of 119 meters, was supported just above the tank bottom. The coil was found to contain a 100 mm section of reduced thickness that was fitted during construction of the tank in 1968 or subsequently during a modification prior to 1980. Corrosion combined with tension induced by shrinkage and expansion caused the steam heating coil to rupture.
After the accident, Vopak introduced measures to avoid future incidents. They include:
• Where possible, steam-based heating will be replaced by heating using warm water.
•Where steam heating is employed, the working pressure of seven bars will be reduced.
• The possibility of developing inspection methods leading to improved quality of steam heating coils will be examined.
• Operations will be reviewed to further reduce any risks of dynamic pressure.