30 large refineries with a very rough replacement cost of say $200bn. Refineries are physically large, especially in Russia, with units widely separated. It is probably difficult to damage more than 10% of the capital stock. The major impact is going to be the disruption of supply of oil products
Components are sanctioned. Evading sanctions adds considerable extra time and cost.
China doesn't follow sanctions.
Russian refineries were built with western parts
That's irrelevant. China knows how to build refineries (2nd world wide) and also how to copy 'western parts'. But then, China could profit, just like India, from russia's pressure to export crude oil. It could bolster their refinery industry which is in decline b/c of electrification of transport.
Then they'd have to redesign from scratch, which takes time and costs extra.
sure. But then, they did not fall from heaven before.