Surface Equipment

Three common types of surface equipment where corrosion can occur are storage tanks, wellheads and flow lines.

Storage Tanks

Storage tanks can be damaged by both external and internal corrosion. External corrosion is most often found at the bottom of the tank, or anywhere the tank comes into contact with water (such as when contacting wet soil). type of corrosion and link. Methods for controlling external corrosion on storage tanks include cathodic protection, coatings and foundations. Internal corrosion often occurs at the inside top of the tank or at the bottom of the tank. Condensation of oxygen(O₂) or hydrogen sulfide (H₂ S) gas often causes the top of the tank to corrode, while salt water or solids settling causes corrosion at the bottom of the tank. The schematic below shows some of the interfaces where corrosion can occur in a surface tank. Many tanks do not vent to the surface due to environmental concerns, which reduces or eliminates the oxygen.

Wellheads

Corrosion is a problem in wellhead and Christmas tree equipment, especially in high pressure, high velocity gas wells. The best practice in these cases is to use equipment constructed out of corrosive resistant materials. The API Specification 6A provides a guide for material requirements (see the references section).

Flow Lines

Flow lines at the surface can corrode due to the presence of water (settling due to gravity to the bottom of the pipe) and/or debris. The layout and sizes of the flow lines can be designed to minimize corrosion, and inhibitors or coatings are also used to mitigate corrosion in these lines. An example of how flow line layout can help prevent erosion corrosion is found in the erosion section.