Petrochemical plants could be damaged (wind and floodwaters) but most will get back on line relatively quickly. Exxon and the Ship Channel industries are all near or above 20' elevation, so even with a 30' storm surge they wouldn't get the full 'punch' that would do huge structural damage, just short-term flooding. Some areas of the Bayport complex get as low as 13', but Hwy 146 and the marshland will blunt some of the force. The Texas City refinery is very low and would likely see the heaviest damage. The Chocolate Bayou plants are only at 10-16', but have some (but not a lot of) marshland protection. Freeport plants could be a problem, they look to be protected by levees with locks to allow a quick drainoff, but the walls appear to be below 14-17'.
Residences, Galveston, and the Bolivar Peninsula is a complete other story.
You appear to know more then I about the elevation of refineries, and you are correct, flooding would just cause short term disruption, the major threat is to homes and business along the coast. Kinda like Katrina did to Ms/Al coast only lots more people here. Big worry for refineries is all the ships along the ship channel breaking loose, I think all that can get out to sea will do so to avoid that. Still to early to predict land fall. Often early predictions are way off.
Time to keep the gas tank full again I see. I made it through Katrina by buying gas before she hit New Orleans. Just filled up again today at $2.64/gallon.