Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium

Definitions

• the invention relates to low alloy steels with high yield strength which have excellent resistance to stress cracking by sulphides.
• the invention aims in particular to apply to tubular products for hydrocarbon wells containing hydrogen sulfide (H 2 S).
• the pressures of the hydrocarbon reservoirs can also be very high, of the order of several hundred bars, and the presence of H 2 S, even at relatively low levels of the order of 10 to 100 ppm, generates partial pressures of the order of 0.001 to 0.1 bar, sufficient when the pH is low to generate if the tube material is not suitable for SSC phenomena.
• the use of low-alloy steels combining a specified minimum yield strength of 862 MPa (125 ksi) or better of 965 MPa (140 ksi) with good SSC resistance would be particularly welcome in such columns. of tubes.
• the patent application EP1862561 proposes a low alloyed steel with a high yield strength (greater than or equal to 862 MPa) and excellent SSC resistance by disclosing a chemical composition advantageously associated with bainitic isothermal transformation heat treatment in the 400-600 temperature range ° C.
• the patent application EP 1 862 561 proposes to increase the C content (between 0.3 and 0.6%) associated with a sufficient addition in Mo and V (respectively greater than or equal to 0.5% and between 0.05 and 0.3%) to obtain a precipitation of carbides MC.
• the patent application EP1862561 proposes an isothermal bainitic transformation heat treatment in the temperature range 400-600 ° C which makes it possible to avoid on the one hand the flaws during the quenching with water of steels with high carbon contents and on the other hand Mixed structures martensite-bainite considered harmful for the SSC in case of softer quenching, for example with oil.
• the bainitic structure obtained (equivalent, according to the patent application EP1862561 the martensitic structure obtained by conventional thermal tempering + tempering treatments) then has a high yield strength (greater than or equal to 862 MPa or 125 ksi) associated with excellent resistance to SSC tested according to NACE TM0177 standards.
• a and D National Association of Corrosion Engineers.
• the remainder of the chemical composition of this steel consists of iron and the impurities or residues resulting from or required for the steel making and casting processes.
• This element is essential to the improvement of the hardenability of the steel and allows obtaining the desired high mechanical characteristics.
• the inventors have furthermore found that relatively high carbon contents provide better resistance to SSC, without such behavior being identified or its reason being known.
• the heat treatment in particular the martensitic quenching in a medium less severe than water, becomes difficult to manage on tubes of great length (10 to 15 meters) and, on the other hand, the amount of carbides formed during the income becomes excessive and can lead to a deterioration of the resistance to the SSC.
• a carbon content down the range indicated above to avoid quenching quenching: for example, a grade will be chosen. in carbon of between 0.32% and 0.38%.
• a quenching system is available with a quenching fluid whose quenching severity is less than that of water (eg, quenching or quenching) added with polymers), it will be advantageous to choose a carbon content upward of the range indicated above: for example a carbon content of between 0.38% and 0.46% will be chosen, and preferably a carbon content of carbon between 0.40 and 0.45%.
• SILICON 0.1% to 1%
• Silicon is a deoxidizing element of liquid steel. A content of at least 0.1% allows such an effect. Silicon also opposes the softening of income and thus contributes to improving the resistance to SSC. Beyond 0.5% it is often written that this element leads to the deterioration of the resistance to the SSC. However, the inventors have found that the Si content can reach 1% without having an adverse effect on the resistance to SSC. This is why its content is set between 0.1% and 1%. A range of between 0.5 and 1% could even be interesting in combination with the other elements of the composition according to the invention.
• PHOSPHORUS less than or equal to 0.03% (impurity)
• Phosphorus is an impurity that degrades resistance to SSC by segregating it at grain boundaries. This is why its content is limited to 0.03%.
• Sulfur is an impurity that forms inclusions that are detrimental to SSC resistance and that can also segregate at grain boundaries. The effect becomes sensitive beyond 0.005%. Therefore, its content is limited to 0.005% and preferably to an extremely low level such as 0.003%.
• Chromium is a useful element for improving the hardenability and mechanical properties of steel and increasing its resistance to SSC. This is why its minimum content is at least 0.3%. However, a level of 1% should not be exceeded to avoid degradation of the SSC resistance.
• MOLYBDENE 1% to 2%
• Molybdenum is a useful element for improving the hardenability of steel and also increases the steel's tempering temperature.
• the inventors have found a particularly favorable effect of Mo contents greater than or equal to 1%.
• the content of this element exceeds 2%, it tends to favor the formation of coarse compounds after increased income at the expense of resistance to SSC. This is why its content is set between 1% and 2%.
• the preferred range is between 1.2% and 1.8%, and most preferably between 1.3% and 1.7%.
• TUNGSTEN 0.3% to 1%
• tungsten is an element that improves the hardenability and strength of steel. This is an important element of the invention which allows not only to tolerate a significant content of Mo without causing the precipitation of large carbides M 23 C 6 and ksi carbides during a high income but on the contrary to promote a fine precipitation and homogeneous micro-carbides MC by limiting their magnification thanks to its low diffusion coefficient. By its effect, tungsten thus makes it possible to increase the molybdenum content to raise the tempering temperature and thus to lower the density of dislocations and to improve the resistance to SSC. A content of at least 0.3% is fixed for this purpose. Beyond 1% its effect does not evolve anymore. This is why the Mo content is set between 0.3% and 1%. The preferred lower and upper limits are 0.4% and 0.7%, respectively.
• VANADIUM 0.03% to 0.25%
• vanadium is a useful element for improving SSC resistance by forming fine micro-carbons TM that can be used to raise the tempering temperature of steel. It must be present at least 0.03% to express its effect. However too abundant precipitation of these carbides tends to weaken the steel. This is why its content is limited to 0.25%.
• the inventors have found a joint influence of the elements Nb and V. When the content of Nb is relatively low (0.01% to 0.03%), the preferred range of V content is between 0.1 and 0.25 % and more preferably between 0.1 and 0.2%.
• Niobium is an additive element that forms carbonitrides with carbon and nitrogen, the anchoring effect of which contributes effectively to grain refinement during austenitization.
• carbonitrides are partially dissolved and niobium has a hardening (or retarding effect on softening) by precipitation of lower-yielding carbonitrides than vanadium.
• the undissolved carbonitrides anchor the austenitic grain boundaries effectively during the austenitization and thus make it possible to obtain a very fine austenitic grain before quenching, which has a very favorable effect on the elastic limit and on the resistance to the SSC.
• this refining effect of the austenitic grain is increased by a double quenching operation.
• this element must be present at least 0.01%.
• Nb carbonitrides are too abundant and relatively coarse, which is not favorable for the resistance to SSC.
• the preferred range of Nb content is between 0.01% and 0.03%.
• VANADIUM + 2xNIOBIUM optionally between 0.10 and 0.35%
• the inventors have found a joint influence of the elements V and Nb on the income delay and therefore on the resistance to the SSC. More Niobium can be added when the V content is relatively low (around 0.04%) and vice versa (rocking effect between these elements).
• the inventors have optionally introduced a limitation on the sum V + 2.Nb which can be between 0.10% and 0.35% and preferably between 0.12 and 0.30%. %.
• ALUMINUM 0.01% to 0.1%
• Aluminum is a powerful deoxidizer of steel and its presence also favors the desulfurization of steel. It is added at a content of at least 0.01% for this. However, at more than 0.1%, on the one hand, the deoxidation and desulphurization of steel is no longer significantly improved and, on the other hand, it tends to form coarse and harmful Al nitrides. This is why the upper limit of Al content is set at 0.1%. The preferred lower and upper limits are 0.01% and 0.05%, respectively.
• Ti content greater than 0.01% promotes the precipitation of TiN titanium nitrides in the liquid phase of the steel and can lead to the formation of large TiN precipitates which are detrimental to SSC resistance.
• Ti contents less than or equal to 0.01% may be impurities resulting from the preparation of the liquid steel and not result from a voluntary addition. Such low levels do not have any detrimental effect on the resistance to SSC for low nitrogen contents (less than or equal to 0.01%) according to the inventors.
• the maximum content of impurity Ti is limited to 0.005%.
• a nitrogen content greater than 0.01% is likely to decrease the SSC resistance of the steel. Its content is therefore preferably kept below 0.01%.
• Boron micro-alloyed steels typically contain titanium to fix nitrogen as TiN compounds and leave boron available.
• the inventors have found on the occasion of the present invention that, for very high yield strength steels to resist SSC, a boron addition was not necessary in the steel according to the invention, or even could to be harmful. Boron is therefore in the form of an impurity in the steel according to the invention.
• Table 1 provides the chemical composition on product (rolled plate) of the three castings tested (all% are expressed by weight).
• Table 1 landmark VS Yes mn P S Cr MB W V AT 0.43 0.79 0 0,010 0,003 0.50 1.46 0.64 0.20 B 0.34 0.36 0.39 0,011 0,003 0.49 1.29 0.52 0.10 VS* 0.33 0.37 0.38 0,011 0,003 0.98 1.50 0,008 * 0.05 landmark Nb V + 2Nb al NOT Ti B AT 0,019 0.24 0.03 0.0045 0,002 0.0005 B 0,021 0.14 0.02 0.0023 0,002 0.0005 VS* 0.081 0.21 0.02 0.0031 0,009 0.0012 * * comparative example
• Castings A and B have a high V content and a low Nb content and casting C an opposite balance for these elements.
• Casting B is a variant of casting A with a lower C and Si content.
• Casting C does not contain W but contains an addition of Ti and boron.
• the casting A was subjected to dilatometric tests for determining the transformation points at the Ac1 and Ac3 heating, the martensitic transformation Ms and Mf temperatures and the martensitic quenching critical speed.
• Ac1 765 ° C.
• Ac3 880 ° C.
• MS 330 ° C.
• Mw 200 ° C.
• the point Ac1 is high and makes it possible to make an income at high temperature.
• the structure obtained with a cooling rate of 20 ° C / s is entirely martensitic and has 15% of bainite for a cooling rate of 7 ° C / s.
• the critical speed of martensitic quenching is thus close to 10 ° C./s.
• Table 2 shows the values of yield strength Rp0.2 and mechanical strength at break Rm obtained on the plates of the various castings after heat treatment of double quenching and tempering.
• Two tempering operations were carried out at temperatures in the region of 950 ° C. in order to better refine the size of the austenitic grains and a tempering between the two quenching operations in order to avoid generating quenching taps between these operations.
• the final income was made between 680 ° C and 730 ° C according to marks A to C to obtain a yield strength value greater than or equal to 965 MPa (140 ksi).
• Rm mechanical strength
• ratio Rp0.2 / Rm close to 0.95 which is favorable to the resistance to the SSC. It is likely desirable that Rm be less than or equal to 1150 MPa and preferably 1120 or even 1100 MPa to promote resistance to SSC.
• Table 4 presents the average values of three Rockwell hardness fingerprints (HRc) made on the samples treated according to Table 2 at three different locations: near each of the surfaces and at mid-thickness of the dishes.
• HRc Rockwell hardness fingerprints
• the maximum values of the table are close to 35 HRc and a maximum value of 36 HRc may appear desirable to promote the SSC.
• Table 5 shows the average values of Charpy V resiliency test results at low temperature (-20 ° C and -40 ° C) on specimens taken longitudinally from the plates of casting A treated according to Table 2.
• Table 5 landmark KV (J) at -40 ° C KV (J) at -20 ° C AT 30 39
• the values obtained are all greater than 27 J (energy value corresponding to the criterion of the API 5CT specification) at -40 ° C.
• Table 6 presents the results of the tests to evaluate the resistance to SSC according to method A of the NACE TM0177 specification.
• test specimens are cylindrical tensile specimens taken from the tubes in the longitudinal direction at mid-thickness of the plates treated according to Table 2 and machined according to the NACE TM0177 Method A specification.
• the test bath used is of type EFC 16 (European Corrosion Federation).
• the aqueous solution is composed of 5% sodium chloride (NaCl) and 0.4% sodium acetate (CH3COONa) with continuous bubbling of the gas mixture 3% H 2 S / 97% CO2 at 24 ° C ( ⁇ 3 ° C) and adjusted to pH 3.5 with hydrochloric acid (HCl).
• the loading stress is set at 85% of the specified minimum yield strength (SMYS), ie 85% of 965 MPa or 820 MPa. Three test pieces are tested under the same test conditions in view of the relative dispersion of this type of test.
• STYS specified minimum yield strength
• the resistance to the SSC is considered good (symbol O) in the absence of rupture of at least two test pieces after 720h and bad (symbol X) if there is a break before the 720h in the calibrated part of at minus two test pieces out of the three tested.
• the tests on marker A have been doubled.
• the steel according to the invention is particularly intended to apply to products intended for the exploration and production of hydrocarbon deposits such as, for example, casing tubes, production tubes (tubing ), tubes for underwater risers, drill pipes, heavy drill rods, drill collars or accessories for the previous products.
• products intended for the exploration and production of hydrocarbon deposits such as, for example, casing tubes, production tubes (tubing ), tubes for underwater risers, drill pipes, heavy drill rods, drill collars or accessories for the previous products.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Articles (AREA)
• Heat Treatment Of Steel (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Continuous Casting (AREA)

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• 2010
  • 2010-06-04 FR FR1054418A patent/FR2960883B1/fr not_active Expired - Fee Related
• 2011
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