The discussion in this chapter concerns itself with any pipeline used for the transportation of materials. Materials involved can include, but are not necessarily limited to, fuel gas, petroleum and petroleum products, water, chemical solutions, effluents from manufacturing plants, and solids being transported in slurry form. Our consideration of corrosion will concern itself with external pipeline corrosion which may occur underground, in a submerged condition, or exposed to the atmosphere. Internal corrosion will be considered for those pipelines carrying material which can be expected to cause internal corrosion under specific conditions. Discussion of corrosion will concern itself with metallic pipelines as opposed to nonmetal pipelines (used in some instances) which are subject to deterioration with time rather than corrosion with time, which is taken as a function of metals only.