Just prior to the rupture of a 55-feet-tall, 8.5-feet diameter monoethanolamine absorber column, a refinery operator noted a six-inch-long horizontal crack at a circumferential weld which was leaking propanes. As the operator attempted to close the inlet valve, the crack spread to about 24 inches. The area was being evacuated and the plant fire brigade was arriving when the column failed massively. Propane at 200 psig at 100°F propelled most of the 20-tonvessel 3,500 feet where it struck and toppled a 138,000-volt power transmission tower. The weld separation occurred along a lower girth weld joint made during a repair to the column 10 years earlier. The vessel was constructed of one-inch thick SA 516 Gr 70 steel plates rolled and welded with full penetration submerged arc joints, but without post-weld heat treatment. This explosion resulted in severe fires in the unsaturated gas plant, and the FCC and the alkylation units. After about 30 minutes, a BLEVE occurred in a large process vessel in the alkylation unit. One piece of this vessel travelled 500 feet, shearing off pipelines before striking a tank in the water treatment unit. Another fragment landed in a unifining unit over 600 feet away, causing a major fire where it landed. The first explosion, believed to be from an unconfined vapor cloud, broke windows up to six miles from the plant, caused extensive structural damage to refinery service buildings and disrupted all electric power at the refinery, rendering a 2,500 US gallons per minute electric fire pump inoperable. One explosion sheared off a hydrant barrel, resulting in a reduction of fire water pressure from the two 2,500 US gallons per minute diesel engine driven fire pumps, which were operating. The refinery’s blast resistant control center, approximately 400 feet northeast of the absorber, sustained little structural damage. An estimated 30 paid and volunteer public fire departments, together with equipment from refineries and chemical plants within a 20-mile radius, responded promptly. Many of the pumpers took suction from the adjoining canal and from a quarry. The pumpers and a 12,000 US gallons/min fireboat eventually provided water at pressures sufficient for fire fighting.

[ Property Damage $191 Million. Estimated Current Value $484 Million ]

Image credit: TWI