Case Study - 4: Pitting of an Oil Pipeline

Major species: Hydrocarbon stream

Minor stream:  Moisture and air

Corrosion deposits and irregular shaped pits

Dirt, dust and debris gets deposited on the external surface of pipe and leads to the formation of differential aeration cells, leading to localized corrosion. These deposits may also induce pitting under deposits. As long as passivity is maintained, localized corrosion does not occur. The passive surface is broken down by the aggressive ions like chloride, found in the debris and deposits leads to pitting.

1. Use 300 series Stainless Steels or austenitic alloys such as 904L
2. Plan maintenance programs to minimize deposit formation
3. Maintain a clean environment around the pipe.