Site Organization
Click here for an outline of
the pages of this site.
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 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 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 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
- Dealloying
- 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.
