Exploration of the causes of corrosion

Pipeline corrosion can be caused by the following factors: 1. High levels of corrosive gases such as H2S and CO2, which combine with water to form acidic media, leading to acid corrosion. 2. The presence of O2 can cause oxidative corrosion. 3. Microbial action can lead to microbial corrosion. 4. The presence of harmful ions such as chloride and sulfate can exacerbate corrosion problems. 5. Under high pressure, the flow velocity inside the pipeline increases, which may lead to erosion corrosion. 6. Although the operating temperature is at room temperature, changes in temperature differences can also promote corrosion. .

The gas contains no hydrogen sulfide, and the pattern of corrosion caused by CO2 corrosion appears different

In the absence of hydrogen sulfide, the possibility of sulfide stress corrosion and hydrogen sulfide corrosion can be ruled out. However, CO2 corrosion can still occur, and it may manifest as uniform or localized corrosion. CO2 reacts with water to form carbonic acid, which lowers the pH value and accelerates the corrosion of metal materials. Furthermore, the severe corrosion at the bottom of the pipeline may be related to water accumulation; the dissolution of CO2 in the aqueous phase leads to the formation of a locally acidic environment, thereby causing localized corrosion. If sediment forms, it may also lead to increased corrosion in the lower areas. Furthermore, due to the high-pressure conditions, the corrosivity of CO2 increases under high pressure. Taking these factors into account, a detailed chemical composition analysis and microstructural analysis of the corroded areas are necessary in order to determine the exact corrosion mechanism. .

Check it out: Summary of corrosion risks and protective measures in gas pipelines; it seems to be related to C02 corrosion

During oil and gas extraction, cases of corrosion of the downhole tubing string, or even severe damage to it, caused by CO2 present in oil and gas, occur frequently. In aqueous media, CO2 can cause rapid general corrosion as well as severe local corrosion in steel. Typical characteristics of CO2-induced corrosion include localized pitting, ring-shaped corrosion, and tabletop-like corrosion.

Corrosion caused by sulfides and hydrogen sulfide can be ruled out. If it is corrosion due to carbon dioxide, then what is the main product of this corrosion? One can try to use XRD to determine what the phase composition is; it’s difficult to judge based solely on the morphology, as the medium isn’t a single substance – tabletop-like corrosion can occur when many materials are mixed together, and the presence of various undesirable elements may also play a role. Pitting is not the only one either……

Pay special attention to the phases of ferric carbonate and ferrous carbonate; if they are present, it could be carbon dioxide corrosion. Take a look at this article – there seems to be a lot of useful information in it. It is recommended to read it several times; if three times isn’t enough, try five times: https://gas.in-en.com/html/gas-3401619.shtml

It can basically be determined as CO2 corrosion. 1. The morphology of the corrosion matches the characteristics of carbonic acid corrosion； 2. The corrosion occurs in the bent section, where increased flow velocity and turbulence accelerate carbonation corrosion ； 3. Although the mole fraction of CO2 is low, the high total pressure results in a CO2 partial pressure of around 0.06 MPa, posing a risk of carbonation corrosion ； 4. Corrosion occurs at the bottom of the pipeline, which is likely the area where water deposits accumulate; this area is more prone to corrosion.

The possibility that carbon dioxide corrosion is the dominant factor is relatively low, for two reasons: 1. Most of the pipes currently in use are under conditions similar to those involving moisture and a comparable CO2 partial pressure; they are also made of the same material, yet corrosion only occurred in this specific area. 2. We subsequently conducted tests using materials such as L360QS, L245NS, and 316L – the sulfur-resistant materials L360QS/L245NS did not provide any significant improvement in terms of resistance to corrosion, while only 316L was able to resist it.