Three common types of surface equipment where corrosion can occur are storage
tanks, wellheads and flow lines.
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.
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
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
For lines buried below the surface, differential aeration is also a source of corrosion
potential. Refer to the oxygen section for more information.