Corrosion and Cathodic Protection Condition for Buried Steel Pipelines Heated by Internal Fluids

It has been widely recognized that buried steel pipelines can be protected effectively by the combined use of protective coatings and cathodic protection.Particular considerations are prerequisite to apply the protective coatings and cathodic protection for buried steel pipelines heated by internal fluid, such as, pipelines of district heating and cooling system, pipelines of gas and petroleum plant, and pipelines transferring crude oil.This paper describes the laboratory studies on the cathodic protection potential and protective current density for buried steel pipelines heated by internal fluids. The studies were performed with soils submerged by water in the temperature range from 40°C to 90°C.At 40°C of the steel surface, a criterion of cathodic protection potentials more negative than -0.85V (Cu/CuSO4) was proposed.In the temperature range from 60°C to 90°C of the steel surface, a criterion of cathodic protection potentials more negative than -0.95V (Cu/CuSO4) was proposed.In the temperature range from 40°C to 60°C, the laboratory study was not performed. However, in this temperature range, a criterion of cathodic protection potentials more negative than -0.95V (Cu/CuSO4) shall be adopted from the safety point of view.