Materials selection for carbon dioxide corrosion
Thread Content
For operating conditions with a carbon dioxide content of 6% and a working pressure of 6.8 MPa, can carbon steel or low-alloy steel be used? Should one still choose stainless steel?
Carbon dioxide itself is not corrosive; corrosion occurs only when acids are formed. And what is 94% of that? What is the operating temperature?
Q245R or Q345R, internal anti-corrosion + sacrificial anode (if there is a liquid phase)
Carbon steel can be used, but strict control is required over the material properties: 1. Carbon equivalent, as well as limits on sulfur, phosphorus, and manganese; 2. The heat treatment state of the material; 3. Material testing; 4. Overall heat treatment of the equipment and low-temperature impact testing of the material; 5. Inspection, grinding, and pre-stretching of welded joints; 6. Control of the temperature during pressure testing; 7. Operating instructions for starting up and shutting down the equipment; 8. Rust removal, grinding, and painting of the equipment
If stainless steel is used, the following points should be noted: 1. Use in the solution-treated state; 2. Acid washing and passivation treatment; 3. Degreasing treatment; 4. Control of chloride ions; 5. Surface inspection of forgings and fittings
The medium is natural gas, containing 6% carbon dioxide, with a temperature of around 40 degrees
Low-alloy steel is sufficient for natural gas; if the natural gas contains hydrogen sulfide, the tendency to stress corrosion must be taken into account. Carbon dioxide is no problem.
When carbon dioxide is present, stress corrosion must be taken into consideration; it has a synergistic effect with hydrogen sulfide
There is no corrosion without liquid water; otherwise, stainless steel should be chosen. Carbon dioxide causes stress corrosion – I heard about this for the first time...
Anything that contains water will definitely corrode. To avoid carbon dioxide corrosion, it is necessary to confirm whether the gas source has been dehydrated (that is, dried using a dryer). It is best to have the user provide a report on the moisture content of the medium. If dehydration is not sufficient, it is personally recommended to use 300 series stainless steel. Additionally: CO2 itself does not have a tendency for stress corrosion; it is carbonates that cause stress corrosion. H2S also requires a humid environment to cause stress corrosion.