Study of the effect of test parameters on the assessment of steel resistance to carbon dioxide corrosion

Carbon dioxide (CO2) corrosion is one of the most dangerous types of destruction of metal products in the oil and gas industry. The field steel pipelines and tubing run the highest risk. Laboratory tests are carried out to assess the resistance of steels to carbon dioxide corrosion. However, unified requirements for certain test parameters are currently absent in the regulatory documentation. We present the results of studying the effect of the parameters of laboratory tests on the assessment of the resistance of steels to CO2 corrosion. It is shown that change in the parameters of CO2 concentration, chemical composition of the water/brine system, the buffer properties and pH, the roughness of the sample surface, etc., even in the framework of the same laboratory technique, can lead in different test results. The main contribution to the repeatability and reproducibility of test results is made by the concentration of CO2, pH of the water/brine system, and surface roughness of the samples. The results obtained can be used in developing recommendations for the choice of test parameters to ensure a satisfactory convergence of the results gained in different laboratories, as well as in elaborating of a unified method for assessing the resistance of steels to carbon dioxide corrosion.

Media corrosiveness and materials resistance at presence of aggressive carbon dioxide

At the present stage of gas field development, the products of many mining facilities have increased content of corrosive CO2 . The corrosive effect of CO2 on steel equipment and pipelines is determined by the conditions of its use. CO2 has a potentially wide range of usage at oil and gas facilities for solving technological problems (during production, transportation, storage, etc.). Simulation tests and analysis were carried out to assess the corrosion effect of CO2 on typical steels (carbon, low-alloy and alloyed) used at field facilities. Gas production facilities demonstrate several corrosion formation zones: lower part of the pipe (when moisture accumulates) and top of the pipe (in case of moisture condensation). The authors have analyzed the main factors influencing the intensity of carbon dioxide corrosion processes at hydrocarbon production with CO2 , its storage and use for various technological purposes. The main mechanism for development of carbon dioxide corrosion is presence/condensation of moisture, which triggers the corrosion process, including the formation of local defects (pits, etc.). X-ray diffraction was used for the analysis of corrosion products formed on the steel surface, which can have different protective characteristics depending on the phase state (amorphous or crystalline).

The Local Corrosion Rate Determination According to Weight Measurements Corrosion Coupons in Oilfield Conditions

Complications associated with a corrosive environment, according to Rosneft's data as of 01.01.2020, are among the prevailing at oil and gas production facilities and rank fourth among other factors complicating production - 12% the complicated mechanized wells. Failures due to corrosion are the second largest complicating factors. Based on the results of approbation, the article proposes a method for calculating the maximum rate of local carbon dioxide corrosion, applicable in oilfield conditions, including to complicated stocks of oil wells and pipelines of oil gathering systems. Based on the approbation results, a method for calculating the maximum rate of local carbon dioxide corrosion, applicable in oilfield conditions, including to complicated stocks of oil wells and oil gathering pipelines systems is proposed in the article. The proposed technique is realizable according to the results one of "traditional" methods the corrosion monitoring - weight (or gravimetric). The approbation results and application possibility the technique in the pilot tests process in assessing the protective ability of corrosion inhibitors and the selection the effective dosages in relation to local damages, which are the main cause the oilfield equipment failures according the factor "Corrosive aggressiveness" (one of the complicating factors in terms of gradation, adopted in the Rosneft Company regulations). On practical examples the oilfield equipment operation, the results of corrosion monitoring and the summary statistics the corrosive stock of wells (using the example of an oil Company), the current situation with respect to this type of complication and relevance the issue under consideration is shown.

Estimation of corrosion aggression of aquatic media and corrosion resistance of steels of equipment of oil and gas condensate deposits

Corrosion destruction of the metal of the field equipment and gas pipelines of the oil and gas condensate field (OGCF) was revealed, the cause of which is carbon dioxide corrosion. In order to determine the corrosiveness of the OGCF equipment media, laboratory tests were carried out with periodic moisture condensation in an atmosphere of carbon dioxide, autoclave tests in the liquid phase at elevated temperatures and partial pressure of CO2, and laboratory tests in the gas-vapor phase in the presence of CO2. Tests were carried out on steel 20, the selected solutions were tested on pipe segments of 09G2S steels (well connections and loops) and J55LT (tubing) of 2 types (old, after operation in a well, and new, not operated). Studies have shown that steels used at OGCF (steel 20, J55LT and 09G2S) are not resistant to carbon dioxide corrosion. All items of equipment made of these steels will be potentially weakly resistant to corrosion in the oil and gas condensate field. It is proposed to conduct tests of corrosion inhibitors from various manufacturers in laboratory and field conditions. Recommendations are given for the corrosion inhibitor selected according to the test results. Keywords: local corrosion; aggressiveness of the environment; metal resistance; well piping; plume; tubing; laboratory tests; autoclave tests.

Analysis of regulatory requirements for the assessment of carbon dioxide corrosion at gas production facilities

Aim.In many fields, the produced gas contains corrosive CO2, which, in combination with moisture and other factors, stimulates the intensive development of corrosion processes, including local ones, which requires careful attention to the assessment of the corrosiveness of operating fluids in order to select effective anti-corrosion protection. Ensuring reliable and safe operation of equipment and pipelines prevents not only man-made risks, but also no less important environmental risks, which are especially dangerous for marine underwater facilities for Arctic coastal facilities.Methods.The analysis of normative and technical documentation in the field of assessment of corrosion risks, aggressive factors of internal corrosion and operating conditions of gas and gas condensate fields has been carried out.Results.One of the criteria for assessing the corrosion hazard is the corrosion rate of steel under operating conditions. However, the normative documents predominantly regulate the general corrosion rate, which evaluates the uniform thinning of the metal. But the rate of local corrosion is in no way taken into account, which is most relevant precisely for the conditions of carbon dioxide corrosion of steel. Another tool for identifying risks can be a corrosion allowance to the pipe wall thickness, which should be selected at the design stage and which is provided to compensate for corrosion losses during the operation of gas pipelines. It is shown that the minimum corrosion allowance (3 mm) specified in the main regulatory documents is insufficient, especially for offshore facilities.Conclusion.The experience of operating gas production facilities confirms that the rate of local corrosion can reach several mm/year. To limit this, effective anti-corrosion measures should be chosen, for example, the use of corrosion inhibitors, and a reasonable level of corrosion allowance should be provided that would take into account the corresponding level of corrosion risks at the gas production facility.

Local corrosion: calculation in oil field conditions (according to weight measurements)

Complications associated with a corrosive environment, according to Rosneft’s data at 01.01.2020, are among the prevailing at oil and gas production facilities and rank fourth among other factors complicating production – 12% the complicated mechanized wells. Failures due to corrosion are the second largest complicating factors. Based on the results of approbation, the article proposes a method for calculating the maximum rate of local carbon dioxide corrosion, applicable in oilfield conditions, including to complicated stocks of oil wells and pipelines of oil gathering systems. Based on the approbation results, a method for calculating the maximum rate of local carbon dioxide corrosion, applicable in oilfield conditions, including to complicated stocks of oil wells and oil-gathering pipelines systems is proposed in the article. The proposed technique is realizable according to the results one of «traditional» methods the corrosion monitoring - weight (or gravimetric). The approbation results and application possibility of the technique in the pilot tests process in assessing the protective ability of corrosion inhibitors and the selection of the effective dosages in relation to local damages, which are the main cause the oilfield equipment failures according the factor «Corrosive aggressiveness» (one of the complicating factors in terms of gradation, adopted in the Rosneft Company regulations). On practical examples the oilfield equipment operation, the results of corrosion monitoring and the summary statistics the corrosive stock of wells (using the example of an oil Company), the current situation with respect to this type of complication and relevance the issue under consideration is shown.

Hazard Assessment of the Internal Carbon Dioxide Corrosion of the Field Pipelines at the Gas and Gas Condensate Fields

At many gas and gas condensate fields in operation, carbon dioxide (СО2) is present in the scope of the produced products, which, in combination with the natural and technological factors, stimulates intensive development of the internal corrosion processes in the pipelines and equipment. The relevance of the development of native regulatory documentation aimed at the assessment of the corrosion effects and development of the practical recommendations for protection against carbon dioxide corrosion in the last decade is due to the development of new gas fields in Russia with a high CO2 content (including on the Russian offshore), where there is a risk of local corrosion development with a high flow rate. The presence of CO2 in the produced gas in combination with the moisture and other factors stimulates the intensive development of corrosion processes and requires careful attention to the assessment of the corrosion aggressiveness of operating environments for selecting an efficient anti-corrosion protection. This is required to ensure reliable and safe operation of the equipment and pipelines made of carbon steel. Pipe low-alloy steel of 09G2S (09Mn2Si) grade, which is the most widely used at the domestic gas facilities, is not resistant to carbon dioxide corrosion. The experience of operating foreign deposits under conditions of carbon dioxide corrosion confirms the need and efficiency of considering this corrosion aspect at the facilities design stage. Incorrect assessment and underestimation of CO2 hazard in the produced hydrocarbons in relation to steel equipment and pipelines can lead to unaccounted corrosion risks (up to the facility shutdown), significant costs for the elimination of corrosion consequences (repairs, etc.), and the need to select and justify urgent corrective measures. Accounting the Russian and international experience allows to make a reasonable choice of rational technical solutions for efficient and safe operation of the deposits in conditions of carbon dioxide corrosion.

Universalism of inhibitors against hydrogen sulfide and carbon dioxide corrosion of carbon steel

The universality of inhibitors is understood as their ability to inhibit several types of corrosion attack: hydrogen sulfide and carbon dioxide corrosion, hydrogen diffusion into metal, development of sulfate-reducing and other types of bacteria, negative impact on the mechanical properties of metals. Indicators of universalism of new inhibitor have been studied. Producer of the inhibiting compositions is Limited Liability Company «INCORGAZ» (S-Petersburg, Russia). The efficacy of the inhibitor in the concentration of 25 - 200 mg/L has been studied with respect to carbon steel in a highly mineralized chloride medium (pH= 6) and NACE medium (5 g/L NaCl, 0.25 g/L CH3COOH, pH =3.5) containing H2S (50-400 mg/L) and CO2 (1at) separately and together. The bactericidal properties of the inhibitor were studied with respect to sulfate-reducing bacteria in the Postgate medium. The investigations were carried out by the methods of linear polarization resistance, electrochemical impedance spectroscopy, gravimetry, potentiodynamic polarization. The protective effectiveness of the inhibitor reaches 80% in the presence of CO2 and 90% in hydrogen sulphide environments. The inhibitor repeatedly reduces the number of sulfate-reducing bacteria and the production of biogenic hydrogen sulfide and inhibits the diffusion of hydrogen into steel.

Laboratory simulation of carbon dioxide corrosion, influence of alloying elements and hydrochloric acid on the structure and protective properties of corrosion products

The paper considers the modeling of CO2-corrosion on chromium-containing steels 1-5%. Study of the protective properties of a layer of corrosion products on steels with a chromium content of 1-5% and the effect of periodic hydrochloric acid treatments.

Increased operational reliability tubing from steel 25CrMnNb grade

The conventional tubing supplied to oilfields with low aggressive environments: with pCO2 up to 0.3 atm and pH2S up to 0.005 atm often shows signs of pitting carbon dioxide corrosion after operation. To solve the problem, a new sparingly alloyed steel of 25KhGB was developed for K steel grade tubing with increased set of performance characteristics obtained after thermomechanical treatment.