Potted citrus can do very well here in 7B, so I'd imagine they'd do just as well or better for you in 8A. I grow limes myself, which are a little easier than oranges, but I know several people who grow Valencia in pots and they do fine. There's an art to keeping them alive year after year, though, and I haven't gotten to that point yet...only in my second year. I'm sure someone else will chime in with some advice on that. But go for it!...citrus in NC is too tempting to not try it!

Have you considered planting cold-hardy citrus in the ground instead? I'm near Wilmington & McKenzie Farms in South Carolina has quite a few varieties that thrive here.

Here is a link that might be useful: McKenzie Farms

I'm in zone 7b (Raleigh NC) and I grow many citrus (some in pots and some in the ground). Oranges have been the hardest to get a decent crop from. Easy to grow, easy to overwinter indoors, great early spring bloom but most of the fruit fall off before summer heat sets in. Blood oranges have been slightly better than Navel oranges. All the tangerines have been better than any of the oranges. Lemons next and then limes. Calamondins and kumquats perform better than any of the others with Calamondins always in bloom and always in fruit throughout the year - but they are insanely sour and most folks don't like the flavor.