Internal corrosion defect types

While Type B sleeves have to be fillet welded to the pipeline (Figure 4.11), they can be used where composite repairs cannot, such as for repair of defects that are 80% deep or greater, circumferentially oriented defects, leaking defects or for defects that will eventually leak (e.g., internal corrosion), and cracks. The raw materials required to make Type B sleeves are significantly less expensive than composite materials, and the stiffness and long-term performance of Type B sleeves are equivalent to that of line pipe steel. 

A similar danger of corrosion lies in cell formation in steel-concrete foundations (see Section 4.3). Such steel-concrete cells are today the most frequent cause of the increasing amount of premature damage at defects in the coating of new steel pipelines. The incidence of this type of cell formation is increased by the connection of potential-equalizing conductors in internal gas pipelines and domestic water pipelines [25], as well as by the increased use of reinforcing steel in concrete foundations for grounding electrical installations [26]. 

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