METHOD FOR PRODUCING A PRESSURE VESSEL

Abstract

The present invention relates to a method of manufacturing a pressure vessel.

Claims

1. A method of manufacturing a pressure vessel having a base at one end of the pressure vessel, a wall section, and a neck section which is at the opposite end of the pressure vessel from the base and has an opening, wherein the method comprises the following steps: providing at least a first blank, where the first blank consists of a carbon steel; creating the wall section from the at least first blank by flow forming to give a pressure vessel preform; creating the neck section from the pressure vessel preform by swivel forming to give a pressure vessel; wherein the pressure vessel, after the swivel forming, is heated at least partly to a temperature Ac1 at which the microstructure of the carbon steel is transformed at least partly to austenite and then cooled down at least in sections by active cooling such that the microstructure is at least partly transformed to martensite and/or bainite, and hence a tensile strength R m of at least 1000 MPa is established at least in sections of the carbon steel of the pressure vessel.

2. The method as claimed in claim 1, wherein the creation of the pressure vessel preform is preceded by forming of a base in the at least first blank in a deep drawing step.

3. The method as claimed in claim 2, wherein active heating is conducted at least in some regions at least one of before and during the creation of the pressure vessel preform and/or of the neck section.

4. The method as claimed in claim 3, wherein the active heating is conducted at a temperature of at least 300? C.

5. The method as claimed in claim 3, wherein the carbon steel, as well as Fe and unavoidable impurities from the production, contains the following chemical elements in % by weight: TABLE-US-00006 C: 0.01 to 0.7%, Si: 0.01 to 3.0%, Mn: 0.01 to 3.0%, N: up to 0.1%, P: up to 0.1%, S: up to 0.1%;

6. The method as claimed in claim 5, wherein a second blank consisting of an austenitic steel is provided.

7. The method as claimed in claim 6, wherein the austenitic steel, as well as Fe and unavoidable impurities from the production, contains the following chemical elements in % by weight: TABLE-US-00007 Cr: 11.0 to 22.0%, Ni: 5.0 to 15.0%, C: up to 0.2%, Si: up to 1.5%, Mn: up to 3.0%, N: up to 0.2%, P: up to 0.1%, S: up to 0.1%.

8. The method as claimed in claim 6, wherein the austenitic steel, as well as Fe and unavoidable impurities from the production, contains the following chemical elements in % by weight: TABLE-US-00008 C: up to 0.6%, Si: up to 1.5%, Mn: 4.0 to 25.0%, N: up to 0.2%, P: up to 0.1%, S: up to 0.1%

9. The method as claimed in claim 8, wherein the second blank is provided simultaneously with the first blank and the creating of the wall section from the two blanks is performed by flow forming to give a pressure vessel preform, and then the neck section is created from the pressure vessel preform by swivel forming to give a pressure vessel.

10. The method as claimed in claim 8, wherein the second blank is provided separately, wherein the second blank is used to create a wall section by flow forming to give a pressure vessel preform, wherein the external diameter (Da) of the pressure vessel preform made from the second blank is equal to or less than the internal diameter (di) of the pressure vessel preform produced by flow forming from the first blank, wherein the pressure vessel preform made from the second blank is then introduced into the pressure vessel preform made from the first blank before the neck section is created from the pressure vessel preforms by swivel forming to give a pressure vessel.

11. The use of a pressure vessel produced as claimed in claim 10 for storage of pressurized fluids in mobile applications.

12. The method of claim 5 wherein the carbon steel, as well as Fe and unavoidable impurities from the production, contains the following chemical elements in % by weight: at least one or more than one element from the group of (Al, Cr, Cu, Mo, Ni, Nb, Ti, V, B, Sn, Ca, REM): TABLE-US-00009 Al: up to 1.0%, Cr: up to 1.0%, Cu: up to 1.0%, Mo: up to 1.0%, Ni: up to 1.0%, Nb: up to 0.2%, Ti: up to 0.2%, V: up to 0.2%, B: up to 0.01%, Sn: up to 0.1%, Ca: up to 0.1%, REM: up to 0.2%.

13. The method as claimed in claim 8, wherein the austenitic steel, as well as Fe and unavoidable impurities from the production, contains the following chemical elements in % by weight: at least one or more than one element from the group of (Al, Cr, Cu, Mo, Ni, Nb, Ti, V, B, Sn, Ca): TABLE-US-00010 Al: up to 3.0%, Cr: up to 4.0%, Cu: up to 1.0%, Mo: up to 1.0%, Ni: up to 2.0%, Nb: up to 0.5%, Ti: up to 0.5%, V: up to 0.5%, B: up to 0.01%, Sn: up to 0.1%, Ca: up to 0.1%.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0031] There follows a detailed elucidation of the invention with reference to drawings. Identical parts are given the same reference numerals. The individual figures show:

[0032] FIG. 1 a schematic perspective diagram showing provision of a blank,

[0033] FIG. 2 a schematic perspective diagram showing provision of a blank with a base,

[0034] FIG. 3 a schematic perspective diagram showing heating of the blank prior to the creation of the pressure vessel preform,

[0035] FIG. 4 a schematic perspective diagram showing creation of the pressure vessel preform at different times,

[0036] FIG. 5 a schematic perspective partial diagram showing creation of the pressure vessel preform at different times from two blanks,

[0037] FIG. 6 a schematic perspective diagram showing combination of two separately produced pressure vessel preforms and

[0038] FIG. 7 a schematic side view of a finished pressure vessel.

BEST MODE FOR CARRYING OUT THE INVENTION

[0039] FIG. 1 shows a schematic perspective diagram showing provision of a first blank (1). The thickness of the blank (1) may, for example, be between 6 and 16 mm. Depending on the size of the pressure vessel (10) to be finished, the diameter of the blank may vary between 150 and 800 mm. The blank (1) consists of a carbon steel which is hardenable and/or heat-treatable. Examples include steels of C22 or C45 quality, but also manganese-boron steels, for example 22MnB5, 37MnB4.

[0040] FIG. 2 shows a schematic perspective diagram showing provision of a first blank (1) with a base (2). The step in FIG. 2 is optional if the finished pressure vessel (10) is not to have a planar base (2). For instance, prior to the creation of the pressure vessel preform (cf. FIG. 4), a base (2) may be formed into the blank (1) in a deep drawing step, said base (2) pointing outward in the finished pressure vessel (10) (cf. FIG. 7), or, alternatively and not shown here, if the construction space does not permit this, pointing inward in the finished pressure vessel. The deep drawing step for optional forming of the base (2) can be effected in the cold state of the blank (1), or else alternatively in the hot state, at least in the hot state in the region of the base (2) to be created, of the blank (1).

[0041] After the optional deep drawing step for creation of the base (2), FIG. 3 shows a schematic perspective diagram showing heating of the first blank (1) prior to the creation of the pressure vessel preform. The active heating can be effected here at least in some regions, such that at least the regions that still have to be shaped are heated. FIG. 3 shows the example of an inductor that heats only the region of the wall section (3) to be completed. In an alternative which is not shown here, the blank (1) may also be heated in full, in the furnace, by means of inductors or by means of burners.

[0042] FIG. 4 shows a schematic perspective diagram showing creation of the pressure vessel preform at different times. The optional deep drawing has the advantage that the correspondingly manufactured base (2) that has especially been created in the middle of the blank (1) can serve as fixing on the mandrel. The heating, or heating of subregions, need not necessarily be effected outside the apparatus for flow forming, but can also be effected within the apparatus before and/or during the creation of the pressure vessel preform. The heating is effected at a temperature of at least 300? C., where the blank (1) is heated at least in subregions, preferably to a temperature between 400 and 800? C. A pressure disk/roll, as shown schematically in FIG. 4, acts on the blank (1) fixed on the mandrel, and the flow forming creates a pressure vessel preform open to one side. After the flow forming, the base (2) and at least the main part of the wall section (3) have been completed.

[0043] If a second layer, especially an inner layer, is advisable, for example in the case of use of the pressure vessel (10) with hydrogen, a second blank (1.1) of an austenitic steel, especially a medium-Mn or high-Mn steel or preferably a CrNi steel, may be provided separately, in which case the second blank (1.1) is used to create a wall section (3.1), preferably by flow forming, to give a pressure vessel preform. The steps may be conducted analogously to the production of the pressure vessel preform from the first blank (1), in accordance with the steps as shown in FIGS. 1 to 4. It is optionally possible to shape a base (2.1) into the second blank (1.1) (cf. FIG. 2), and the creation of the pressure vessel preform may also be preceded by heating of the second blank (1.1) (cf. FIG. 3). In the flow forming of the individual pressure vessel preforms, it should be ensured that the external diameter (Da) of the pressure vessel preform made from the second blank (1.1) is equal to or less than the internal diameter (di) of the pressure vessel preform created by flow forming from the first blank (1), such that the pressure vessel preform made from the second blank (1.1) can be introduced into the pressure vessel preform made from the first blank (1) (see FIG. 6) before the neck section (4) is created from the pressure vessel preforms by swivel forming to give a pressure vessel (10).

[0044] Alternatively, the second blank (1.1) may be provided simultaneously with the first blank (1), and the creating of the wall section (3) from the two blanks (1, 1.1) can be conducted by flow forming to give a pressure vessel preform. FIG. 5 shows a schematic perspective part-diagram showing creation of the pressure vessel preform at different times from the two blanks (1, 1.1). The two blanks (1, 1.1) are arranged such that, in the finished state, the austenitic steel forms the inner layer and the carbon steel the outer layer of the pressure vessel (10).

[0045] In a step which is not shown, the neck section (4) is formed from the pressure vessel preform by swivel forming to give a pressure vessel (10). For example, this section can be performed in a swivel forming apparatus. Preferably, before and/or during the swivel forming, at least the neck section (4) to be manufactured is heated, preferably to a temperature between 700 and 1100? C., with introduction of an opening (5) in the course of or subsequent to the swivel forming (cf. FIG. 7).

[0046] After the swivel forming, the pressure vessel (10) is at least partly heated to a temperature of Ac1, at which the microstructure of the carbon steel is at least partly converted to austenite, and then is cooled down at least in sections by active cooling in such a way that the microstructure is converted at least partly to martensite and/or bainite, and hence, at least in sections, a tensile strength R.sub.m of at least 1000 MPa is established in the carbon steel of the pressure vessel (10). The pressure vessel (10) is preferably heated completely at least to a temperature of Ac3 and completely cooled actively such that the homogeneous microstructure composed of essentially martensite having a tensile strength of at least 100 MPa, especially of at least 1100 MPa, preferably of at least 1200 MPa, more preferably of at least 1300 MPa, especially preferably of at least 1400 MPa, further preferably of at least 1900 MPa, is established throughout the carbon steel of the pressure vessel (10).

[0047] A final heat treatment may be conducted to increase ductility in the carbon steel of the pressure vessel (10).

[0048] The pressure vessel (10) may thus consist of a single-layer carbon steel or, if hydrogen is to be used as gas, of two individual layers composed of an outer layer of carbon steel and an inner layer of austenitic steel, preferably CrNi steel.