Up to 18% of US ethylene producing capacity had been reduced or shut since Monday by Hurricane Issacs passage through Louisiana, according to a Platts estimate based on information from the companies.

Eleven olefin plants located in Louisiana with a combined production of more than 6.4 million mt/year of ethylene and derivative products were on alert since late Wednesday when Isaac was downgraded to a tropical storm moving away from Louisiana.

Williams shut its 612,000 mt/year steam cracker in Giesmer, Louisiana, on Monday as the storm approached, the company said. The unit will remain offline throughout the remainder of the week, as the company conducts maintenance unrelated to the storm, a company source said Thursday. Also, Dow Chemical went through a planned shutdown of its 598,000 mt/year steam cracker in Saint Charles, Louisiana, Monday.

In addition to the closed facilities, Exxon Mobils Baton Rouge plant and the two Dow facilities in Plaquemine Parish were running at reduced rates, sources said. Shell, which operates two crackers with a combined capacity 1.36 million mt/year) at its Norco petrochemical complex in St. Charles Parish, reported facilities at Norco, Convent and Geismar as well as Mobile, Alabama, were running at reduced rates in a posting on the companys website.

The hampered production was reflected in the ethylene spot market. September product traded Tuesday at 61.25 cents/lb for undisclosed amounts, and another 5 million lbs deal traded at 60 cents/lb, trading sources said. Week-to-week, the spot price for ethylene climbed 3.75 cents/lb ($82/mt), with Thursdays assessment at 61-61.5 cents/lb MtB Wms.