Patent Application
20180312937
The present invention relates to a seamless line pipe used for transporting oil and gas in oil and gas fields. In particular, the present invention relates to a seamless line pipe suitable for use in an environment having carbon dioxide (CO2), hydrogen sulfide (H2S), and sulfate-reducing bacteria (SRB), which has excellent resistance against uniform corrosion, particularly excellent resistance against pitting corrosion, and a manufacturing method thereof.
With the deepening of oil and gas field exploitation and the increasingly harsh working conditions, the produced oil and gas are often accompanied by corrosive gases like CO2 and H2S. Gathering line pipes are mainly used to connect the pipelines between an oil and gas well and an integrated oil and gas processing apparatus, and to transport oil and gas that have not been subjected to pretreatment of dehydration, desalination, and desulfurization. Therefore, gathering line pipes serve under rather stringent conditions. In recent years, due to the frequent leakage accidents of pipelines caused by the CO2-H2S-SRB coexistence environment in domestic oil and gas fields, great economic losses and environmental pressure have been brought to the oil and gas fields. At present, anti-corrosion seamless pipelines that are resistant to only CO2/H2S corrosion cannot effectively solve the perforation problems caused by the CO2-H2S-SRB coexistence environment. Therefore, a seamless line pipe resistant to CO2-H2S-SRB corrosion is highly desired in the oil and gas field industry.
Japanese patent document entitled “A line pipe with excellent acid and corrosion resistance” with publication date of Oct. 15, 1996 and publication No. JP8269623 discloses a line pipe with a chemical element composition of: C≤1.06%, Si 0.01 to 0.50%, Mn 0.1 to 2.0%, P≤1.01%, S≤1.003%, Cr 0.25 to 1.0%, Al 0.01 to 0.10%, Ca≤1.006%, Pcm (%)≤0.18%. The line pipe belongs to low Cr anti-CO2/H2S corrosion line pipe, but its Cr content of only 0.25 to 1.0% has limited contribution to pitting corrosion resistance, not capable of resisting uniform corrosion and localized corrosion in a CO2-H2S-SRB coexistence environment.
Chinese patent document entitled “X70QS seamless line pipe with anti-HIC performance” with publication date of Jun. 20, 2012 and publication No. CN101921964B discloses a seamless line pipe with a chemical composition in mass percentage of C 0.06 to 0.14%, Si 0.20 to 0.45%, Mn 1.00 to 1.30%, P≤0.015%, S≤0.003%, Cr 0.05 to 0.30%, Mo 0.05 to 0.30%, Al 0.015 to 0.060%, N 0.003 to 0.010%, Nb 0.030-0.50%, V 0.05-0.09%, Ni, Cu as residual elements in the steel, with limited contents of Ni≤0.10%, Cu≤0.20%, and balance of Fe and impurities. The line pipe has high strength, excellent impact performance and good anti-HIC performance. However, it does not have excellent resistance against CO2-SRB corrosion.
Chinese patent document entitled “Anti-corrosion seamless gathering line pipe and manufacturing method thereof” with publication date of Mar. 30, 2016, and publication No. CN103147006B discloses a gathering line pipe with a chemical composition in mass percentage of C 0.04 to 0.10%, Si 0.1 to 0.35%, Mn 0.3 to 0.8%, Cr 0.55 to 1.25%, W 0.06 to 0.55%, Al 0.01 to 0.05%, Ca 0.0005 to 0.006%, Cu≤0.2%, Ni≤0.2%, V≤0.05%, Ti≤0.03%, Nb≤0.05%, and balance of Fe and other unavoidable impurities. The gathering line pipe has high strength, excellent welding performance, good impact properties and other comprehensive mechanical properties, together with excellent anti-CO2/H2S corrosion resistance. However, it does not have corrosion resistance against a CO2-H2S-SRB coexistence condition.
According to the study of the present invention, a seamless line pipe having high strength and excellent resistance against CO2-H2S-SRB corrosion can be obtained with appropriate configuration of alloy elements together with appropriate heat treatment conditions.
In view of the above technical problems, the object of the present invention is to provide a seamless line pipe with high strength and excellent resistance against CO2-H2S-SRB corrosion and a manufacturing method thereof.
After studying the relationship among the composition, structure and properties of the material, the inventor found that the performance of the passivation film on the steel surface during CO2-H2S-SRB corrosion is critical while the addition of Cr, Ni, and Cu may improve the performance of the passivation film. The present invention is based on the above findings and its main content is a line pipe comprising the following:
The seamless pipe comprises, by mass fraction, C: 0.03 to 0.10%, Si: 0.1 to 0.5%, Mn: 0.10% to 1.50%, P: 0.02% or less, S: 0.005% or less, Cr: 1.0 to 4.0%, Ni: 0.1 to 1.5%, Cu: 0.15 to 2.0%, Mo: 0.05 to 0.4%, Ti: 0.01 to 0.05%, Re: 0.05 to 0.1%, and balance of Fe.
After smelting, rolling into a billet, piercing and rolling into a pipe followed by quenching+tempering (tempering temperature of 500-700° C.), the line pipe is qualified by inspection and can then be used as a qualified line pipe.
Description is now provided for each item in details in the following:
1) Alloy Composition (Wherein all Contents in Percentage are Mass Fractions)
2) Manufacturing Process
The present invention has the following advantages over other line pipes:
In summary, the present invention can provide a seamless line pipe with excellent resistance against CO2-H2S-SRB corrosion and can be used in the field of oil and gas fluid transportation.
Hereinafter, the technical solutions in the examples of the present invention are clearly and fully described. Obviously, the examples described are only a part but not all of the examples of the present invention. Any other examples obtained by a person of ordinary skill in the art based on the examples of the present invention without making creative efforts shall fall within the scope of the present invention.
The compositions of the examples are shown in Table 1.
Line pipes with a size of 219*14.5 (i.e., diameter*wall thickness) were made of alloys having the compositions shown in Table 1 with the specific procedures as follows:
Alloys having the above compositions were casted into ingots which were then forged into φ300 mm circular billets;
The billets were heated to 1250° C. and kept for 3 hours, and then subjected to a general hot-rolled line pipe production process of piercing, hot rolling, and fixing in diameter to produce pierced pipes;
The resultant pierced pipes were heated to 920 to 1000° C. and kept for 40 minutes before they were quenched using different cooling techniques. Then, each of the steel species was subjected to tempering at 500 to 700° C. for 1 hour. The heat treatment process, performance and corrosion resistance of each line pipe are shown in Table 2.
The data in each category in Table 2 were measured as follows:
The data for yield strength was obtained by processing the prepared line pipe into an API arc sample, and calculating the average number after the API standard test;
The data for full-size Charpy V-shaped impact absorption energy was obtained by calculating the average number after the GB/T 229 standard test performed on a full-size V-shaped impact test specimen with a cross-sectional area of 10*10*55 taken from the prepared steel pipes;
The corrosion test was conducted in an CO2, H2S, SRB coexistence environment. The samples were immersed in the liquid in a vessel at a temperature of 38° C., with a partial pressure of CO2 of 0.1 MPa and a partial pressure of H2S of 0.1 MPa, for a test duration of 168 h. The weights of the samples before and after the test were compared, and the uniform corrosion rates were calculated. The pitting corrosion rates were obtained by analysis of the cross-section area of the pitting holes.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201710284976.X | Apr 2017 | CN | national |
