49 CFR 193.2629
External corrosion control: buried or submerged components.
(a)Each buried or submerged component that is subject to external corrosive attack must be protected from external corrosion by—#
(1)Material that has been designed and selected to resist the corrosive environment involved; or#
(2)The following means:#
(i)An external protective coating designed and installed to prevent corrosion attack and to meet the requirements of § 192.461 of this chapter; and#
(ii)A cathodic protection system designed to protect components in their entirety in accordance with the requirements of § 192.463 of this chapter and placed in operation before October 23, 1981, or within 1 year after the component is constructed or installed, whichever is later.#
(b)Where cathodic protection is applied, components that are electrically interconnected must be protected as a unit.#