S.C. Code Regs. § § 117-311.1
Some railroads maintain storehouses, in South Carolina for the temporary storage of materials and supplies. Some of these materials and supplies are for use in South Carolina and some are for use in other states. Frequently, when materials are shipped to such storehouses, the railroad does not know what materials are for use in South Carolina, and what are for use in other states. Because of the impracticability of determining what proportion of such materials and supplies is subject to the tax at the time of their purchase, and because of the inequity of imposing the tax on the total purchase of such materials and supplies, the railroad may apply for a certificate under the provisions of Section 12-36-2510, which allows such railroad to purchase materials and supplies at wholesale, and to remit the use tax on the materials and supplies withdrawn for use or consumption within this state.
S.C. Code Regs. § 117-311.1