Welcome to the WAIDS Corrosion Pages
The theory pages have basic information and theory on
the main types of corrosion and why the occur. Subheadings include uniform, galvanic,
crevice and pitting, hydrogen damage, environmentally induced, and erosion corrosion.
General information about corrosion can be found below.
The equipment pages have information on the specific
types of corrosion in oilfield equipment. Included are pages for artificial lift
wells, casing and tubing, surface equipment and enhanced oil recovery operations.
The gases pages discuss specific gases in the oil field
that can cause corrosion, including O2, H2S, CO2,
as well as microbially influenced corrosion. Each section has expanded theory on
the different corrosion types, occurrences, pictures of corrosion, and prevention
and/or mitigation techniques.
The prevention page has information on cathodic protection,
coatings, and chemical corrosion inhibitors, with their different types and uses.
This site was developed by Dr. Ibrahim Gundiler, with the assistance of Dr. Sue
Schrader, Naomi Davidson and Nilay Engin. The project is supported by US DOE contract
DE-FC26-02NT15134, under the direction of Martha Cather.
What is corrosion?
Corrosion is defined as the destruction of a metal by a chemical or electrochemical
reaction. Corrosion occurs when a metal in contact with water forms a corrosion
cell. The corrosion cell has four components, the aqueous phase (water) which acts
as an electrolyte (through which ions migrate), an anode on the metal surface (where
the metal is oxidized and goes into solution as metal ions), a cathode (where excess
electrons are consumed) and a metallic path connecting the cathode to the anode.
The corrosion cell
Why does corrosion occur, and how can it be stopped?
When found in nature, most engineering metals are generally in their oxidized state.
During the smelting and refining processes, they are reduced to an inherently unstable
metallic state. Metals corrode to return to their natural form, achieving a lower
energy state. Alloys, which contain other elements, may increase the metal's stability
and make it more corrosion resistant.
In order to control corrosion, the current loop must be broken by stopping the electron
flow using various means. Some ways to control corrosion include electrical means
(cathodic protection), the addition of corrosion inhibitor chemicals, and the application
of non-metallic barriers (coatings). Sometimes the metal generates its own barrier
from corrosion products (e.g. metal oxide); the metal is then in the "passive condition".
One of the most important methods of corrosion prevention is to find an economic
alloy/environment combination where the alloy is in the passive condition and corrodes
at a much slower rate. In production wells, a corrosion rate below 1 mpy (mils per
year, 1 mil = 1/1000 in) is acceptable, while in water systems, a rate of 2 mpy
is a good target.
Important factors that influence oil field corrosion
Factors that influence oilfield corrosion rates include the presence of gasses,
especially CO2, O2, and H2S. These gasses make
the water an aggressive electrolyte. Other influences are flow velocity, metal composition,
temperature, water quality issues(including the pH and presence of microbes, bicarbonates,
chlorides and organic acids), temperature, and pressure.
Environments in the oil field where corrosion occurs
Some corrosive environments include produced waters with corrosive gases such as
CO2, O2, and H2S. Other environments include workover
fluids, acids such as HCl, and the presence of microbes that cause microbially influenced
corrosion. Click on the gases button, then on the various
environment buttons to see pictures of corrosion samples from each environment.
Types of corrosion
The main types of corrosion are
- Uniform corrosion
- Galvanic corrosion
- Intergranular corrosion
- Crevice and pitting corrosion
- Environmentally induced cracking
- Hydrogen damage
- Erosion corrosion
- Stray current corrosion
Click on the theory button to learn about types of corrosion.