S.C. Code Ann. § 15-3-520: Within twenty years.

Within twenty years:

(a) an action upon a bond or other contract in writing secured by a mortgage of real property;

(b) an action upon a sealed instrument, other than a sealed note and personal bond for the payment of money only whereon the period of limitation is the same as prescribed in Section 15-3-530, except that a sealed contract for sale or an offer to buy or sell goods whereon the period of limitation is the same as prescribed in Section 36-2-725.