METHOD OF PRODUCTION OF HIGH-PRESSURE SEAMLESS CYLINDER FROM CORROSION-RESISTANT STEEL

Abstract

Blank of corrosion-resistant steel is coated with coating of water glass with thickness of 20 to 150 m, cured at 15 to 60 C., and heated in an induction furnace to the temperature of 1180 C. to 1260 C. The heated up blank is without cooling by water descaling transferred into an extrusion press and extruded here, while the coating is broken to pieces and largely removed. Drawing in a horizontal drawing press and necking are performed. After forming to the final shape of the cylinder, leftovers of coating are removed by pressure blasting. A corrosion-resistant thin-walled seamless high-pressure cylinder with volume of 5 to 260 litres is manufactured.

Claims

1. Method of production of high-pressure seamless cylinder from corrosion-resistant steel, in which the starting steel blank (1) is heated in an induction furnace and then inserted into an extrusion press where it is upset and backward extruded in two steps, from which during the first step, the blank (1) is inserted into a die (4) with a vertically moving piercing tool (7), and here it is moulded by means of extrusion until a thick-walled hollow semi-product (5) having an inner cavity, walls and bottom is moulded from it, after which this semi-product (5) is removed from the extrusion press, turned by 90, and seated in this position into a horizontal drawing press, where the second step of forming in terms of backward drawing takes place, when during this second step, the semi-product (5) is put on a drawing mandrel having the diameter corresponding to the required final inner diameter of the produced cylinder, and in this drawing press, the semi-product (5) is extruded through a stripper ring and roller cartridges fitted with reduction rollers by means of which it is rolled on the mandrel, while this rolling is performed so long until the semi-product (5) acquires the required outer and inner diameter, after which the final shape of the cylinder bottom is formed by insertion of the semi-product (5) bottom into a sizing die and subsequently, in the course of the backward movement of the drawing mandrel, the semi-product (5) is pulled off from the drawing mandrel with the help of stripping jaws, aftercooled, and subsequently necked, by which the shape of the manufactured cylinder is finished, characterized by that even before heating in the induction furnace, the blank (1) is coated on at least 85% of its surface with coating (2) from material based on water glass with thickness of 20 to 150, this coating (2) is cured by drying at the temperature of 15 to 60 C. and only after this curing, the blank (1) is subjected to heating in the induction furnace.

2. Method of production of high-pressure seamless cylinder from corrosion-resistant steel according to claim 1, characterized by that the material applied to the blank (1) for example by spraying or by brush consists of suspension containing 20 to 40% w. w. of sodium silicate or potassium silicate or mixture of these silicates, and 40 to 80% w. w. of water, while in the case of presence of admixtures such as bore-silicates and/or corrosion inhibitors, the admixtures are contained in the amount of maximum 20% w. w.

3. Method of production of high-pressure seamless cylinder from corrosion-resistant steel according to claim 1 characterized by that the blank (1) with the coating (2) from material based on water glass is heated in the induction furnace to the temperature of 1180 C. to 1260 C.

4. Method of production of high-pressure seamless cylinder from corrosion-resistant steel according to claim 1, characterized by that after the blank (1) with coating (2) is heated up in the induction furnace, the blank (1) with coating (2) is taken out of here and during persistence of its temperature of minimum 1110 C., it is inserted into the extrusion press without performing water jetting of scale between the removal from the induction furnace and insertion into the extrusion press.

5. Method of production of high-pressure seamless cylinder from corrosion-resistant steel according to claim 1, characterized by that during the first step of mechanical working, in the course of piercing, the coating (2) of material based on water glass is broken to pieces by pushing of the piercing tool (7) to the blank (1) and the coating (2) cracks off during extrusion in the extrusion press until at least its predominant part is removed,

6. Method of production of high-pressure seamless cylinder from corrosion-resistant steel according to claim 5, characterized by that after the final shape of the cylinder is formed from the semi-product (5), the leftovers of coating (2) based on water glass are removed from the surface of the semi-product (5) by pressure blasting of its outer as well as inner surface.

7. Method of production of high-pressure seamless cylinder from corrosion-resistant steel according to claim 1, characterized by that the blank (1) is made of corrosion-resistant steel while the resulting cylinder is made as a seamless cylinder in the volume range from 5 litres up to 260 litres, as a single necked or double-necked cylinder for any volume within the said range.

8. Method of production of high-pressure seamless cylinder from corrosion-resistant steel according to claim 7, characterized by that in the second step of forming, the semi-product (5) wall is pressed to the thickness of 2 to 21.5 mm.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0017] The invention is illustrated using drawings, where

[0018] FIG. 1 shows the blank with applied coating of water glass in cross-section,

[0019] FIG. 2 shows the phase of curing of the coating on the blank,

[0020] FIG. 3 shows the phase of relocation of the blank from the induction furnace directly into the extrusion press, and

[0021] FIG. 4 A, B shows process of pressing of the blank in the extrusion press, from which A shows the phase of extrusion of the future cylinder cavity in the blank and B shows the subsequent phase of breaking and falling off of the coating from the semi-product during pressing.

BEST MODE FOR CARRYING OUT THE INVENTION

[0022] Example of embodiment of the invention is visually demonstrated with the help of FIGS. 1 to 4 and the hereinafter-described method of production of corrosion-resistant high-pressure seamless cylinder for storage, transport, and use of natural gas.

[0023] Parts of the size needed for the manufacture of cylinders of the produced volume are first cut from billets of corrosion-resistant steel having square or circular section. Each individual part, i.e. the starting steel blank 1, is on at least 85% of its surface coated with coating 2 from material based on water glass. The thickness of applied layer is 20 to 150 m. Suspension usually called water glass is used as the material based on water glass. For the purposes of the invention, the suspension based on water glass stands for suspension containing 20 to 40% w. w. of sodium silicate or potassium silicate or their mixture and 80 to 40% w. w. of water. Admixtures of borosilicates and corrosion inhibitors such as hexamine, fenylethylamine, phosphates, etc. and/or possible other admixtures can be contained provided they do not exceed the amount of 20% w. w. in the suspension.

[0024] Examples of material composition of the suspension are given below.

TABLE-US-00001 Suspension I weight % in Material the suspension Silicates (sodium or potassium silicate or their mixture) 20 Water 80 Admixtures 0

TABLE-US-00002 Suspension II weight % in Material the suspension Silicates (sodium or potassium silicate or their mixture) 40 Water 60 Admixtures 0

TABLE-US-00003 Suspension III weight % in Material the suspension Silicates (sodium or potassium silicate or their mixture) 30 Water 60 Admixtures (borosilicates and corrosion inhibitors 10 in quantities 1:1)

TABLE-US-00004 Suspension IV weight % in Material the suspension Silicates (sodium or potassium silicate or their mixture) 40 Water 40 Admixtures (borosilicates and unidentified admixtures) 20

[0025] This coating 2 can be applied by brushing or spraying. After the application, the coating is let to dry at the temperature of 15 to 60 C. until curing. Sufficient curing will not take place in the case of curing below the temperature of 15 C., so that unwanted cracking and falling-off of the coating 2 layer would take place during subsequent heating in the induction furnace. In the case of curing above 60 C., unwanted cracking of the coating 2 will take place as soon as during drying. During curing within the said range, creation of homogenous layer acting as a protective jacket on the surface of the blank 1 takes place. For the drying process or after it, the blank 1 is placed into the induction furnace, where it is heated up by gradual heating to the temperature of 1180 C. to 1260 C. During heating, neither high-temperature oxidation of the surface of blanks 1 contained in the induction furnace nor forge welding of more pieces of blanks 1, imminent in the case of heating without the coating 2, takes place. The heated up blank 1 with the coating 2 is removed from the induction furnace by robotic feeder 3 and immediately after removal from the induction furnace it is inserted into a die 4 of extrusion press without significant cooling down, with continuation of its temperature of at least 1110 C.

[0026] When compared with the process used until now, the step of descaling by water jetting of scale, which is always performed during the existing process between the removal from the induction furnace and insertion into the extrusion press, is skipped. Skipping of the up to now necessary step of water jetting of scale is very significant, because this is preventing cooling down by more than 80 C., thus eliminating formation of temperature gradient and temperature fluctuations that are typical during the clearing of high-temperature-heating generated scale by means of high-pressure water jet descaling. In addition, the possibility of precise control of the blank 1 temperature is achieved by skipping the descaling.

[0027] In the extrusion press, the blank 1 and later the semi-product 5 created from it is upset and backward extruded in two steps. From this, during the first step, the blank 1 is placed at the bottom 6 of the extrusion press die 4 and here it is pressed by vertically moving ram ended with a piercing mandrel constituting the piercing tool 7. The blank 1 is moulded here by means of extrusion until a thick-walled hollow semi-product 5 having an inner cavity, walls, and bottom is moulded from it, as shown on FIGS. 4 A, B. During this first step of mechanical working, in the course of piercing, the coating 2 of material based on water glass is broken to pieces by pushing of the piercing tool 7 to the blank 1 and the semi-product 5 made of it, the coating 2 cracks off, and approximately all this coating 2 is removed during extrusion in the extrusion press. During extrusion, the water glass admixtures will make their way from the coating 2 into the surface layer of the semi-product 5 to the depth of maximum 10 m, these leftovers are removed later by blasting. The aforementioned extrusion takes place during continuation of the semi-product 5 temperature at 1100 to 1200 C. Homogenous moulding of the first semi-product 5 does not take place and transversal cracks appear on the semi-product 5 body at a lower temperature. On the contrary, when exceeding the temperature above 1200 C., oxidation of primary austenitic grains occurs and so called burning out of the material takes place and hence its irreversible degradation. Without using the coating 2, the semi-product 5 could not be extruded and drawn to the required shape, or the corrosion-resistant steel could not be used as the material and/or the result could not lead to the production of the thin-walled seamless high-pressure cylinder of required mechanical and pressure strength.

[0028] After completion of processing in the extrusion press, the semi-product 5 is removed from the extrusion press, turned by 90, and seated in this position into a horizontal drawing press, where the second step of forming in terms of backward drawing takes place. During this second step, the semi-product 5 is put on a drawing mandrel having the diameter corresponding to the desired final inner diameter of the produced cylinder, and in this drawing press, the semi-product 5 is extruded through a stripper ring and roller cartridges fitted with reduction rollers by means of which it is rolled on the mandrel. Rolling is performed so long until the semi-product 5 acquires the required outer and inner diameter. Then the final shape of the cylinder bottom is formed by insertion of the semi-product 5 bottom into a sizing die and subsequently, in the course of the backward movement of the drawing mandrel, the semi-product 5 is pulled off from the drawing mandrel with the help of stripping jaws, aftercooled, and subsequently necked by already known method by means of rotary forming or die forging process. The shape of the manufactured cylinder is finished in this way.

[0029] Leftovers of the water glass based coating 2 are removed from the surface of the semi-product 5 by pressure blasting of its outer as well as inner surface with abrasive for example of steel-shot and cast-iron grit.

[0030] Corrosion-resistant seamless pressure cylinders in the volume range from 5 litres up to 260 litres can be manufactured using the method according to the invention for any volume within the said range as single necked or double-necked cylinders. In the second step of forming, the invention allows pressing the semi-product 5 wall even to the thickness of a thin-walled cylinder without loss of qualitative properties of the manufactured cylinder. The semi-product 5 wall is pressed even to the thickness of 2 to 21.5 mm. In so doing, the cylinder wall thickness is selected in concrete terms within the above said range depending on the required cylinder volume, pressure for which the cylinder is designated, and requirements for qualitative properties and mechanical strength of the cylinder.

[0031] Figures FIG. 1 to 4 illustrate only the steps related directly to the new steps of the process of production of the cylinder according to the invention. The other steps and processes that are already known in this field and are described in the Background Art paragraph do not need to be illuminated using figures.