Cylindrical shell for use in gas cylinder fabrication

#The present invention relates to a method of producing a cylindrical shell used for fabricating a gas cylinder to contain a gas. More particularly, the present invention relates to such a method in which a billet of circular, transverse cross-section is used to form the cylindrical shell by billet piercing. Even more particularly, the present invention relates to such a method in which the billet is formed of a first section of steel and a second section of liner material so that the cylindrical shell has an outer cylindrical form made of steel and an inner liner insert formed of the liner insert material.

#Gas cylinders are widely used in various industries for storing gases. The storage of ultra-high purity gases used within the semiconductor industry is particularly problematical due their corrosive nature. Such corrosion can produce particulate contamination that in turn can produce unacceptable manufacturing defects. For instance, corrosive etching gases such as hydrogen chloride can corrode steel cylinders to produce particulate contaminants. If the resultant particulate material is drawn into a stage of the semiconductor manufacturing process, the product of such stage might be ruined.

#Thus, gas cylinders have been specifically designed to maintain the purity of the gas by being fabricated of nickel. As may be appreciated, nickel gas cylinders are prohibitively expensive. Additionally, pure nickel cylinders generally cannot be used where the intended service pressure exceeds 35.15 kg./cm.sup.2. As a result, gas cylinders for high purity gas storage applications are formed with an outer layer of steel for structural integrity and an inner nickel plating for corrosion resistance.

#While the specification concludes with claims distinctively pointing out the subject matter that applicants regard as their invention, it is believed that the invention will be better understood when taken in connection with the accompanying drawings in which:

#FIG. 1 is a cross-sectional view of a billet used in carrying out a method in accordance with the present invention;

#FIG. 2 is a cross-sectional view of the billet shown in FIG. 1 after completion a cupping operation;

#With reference to FIG. 1, a billet 1 for carrying out a method in accordance with the present invention is illustrated. Billet 1 has a circular, transfer-cross-section and is formed of first and second sections 10 and 20. Section 10 is fabricated from 4130 steel and has an end portion 14 provided with a recess 16 defined within end portion 14. Second section 12 is formed of a liner insert material which is shaped to nest within recess 16 of end portion 14. In gas cylinder used to retain specialty gases, the liner insert material is a corrosive resistant nickel or nickel alloy. Liner insert materials of Hastalloy C-22, tantalum, titanium, gold, or platinum are possible. As illustrated, recess 16 has a conical side wall and thus, second section 12 is a frustum of a cone to nest within recess 16. Other shapes are possible, such as hemispherical shapes.

#A series of billet dimensions were modeled using finite element techniques. FIGS. 2 through 4 represent the results of modeling a billet 1 with a height of about 22.86 cm and a diameter of about 20.32 cm. Second layer 12 was modeled as nickel with a thickness of about 5.08 cm, a top surface diameter of about 17.78 cm and a bottom surface diameter of about 15.24 cm.

#With specific reference to FIG. 2, billet 1 has been pierced by a mandrel to produce a cup-like form 3. Cup-like form 3 has an inner layer of nickel 18 derived from liner insert material 12 and an outer portion 20 that is derived from first section 10 of steel.