Patent GB-1155174-A (GB)
Title: Improvements relating to the Forming Of Pressure Vessels
IPC: B21D51/24
Filed: 1966-06-27
Abstract: 1,155,174. Making pressure vessels; welding. FOSTER WHEELER CORP. 27 June, 1966 [25 June, 1965], No. 28638/66. Headings B3A, B3Q, B3R and B3V. [Also in Division F3] A method of making a pressure vessel comprises explosively forming a first part, connecting this to a second part and explosively expanding the second part. In an example, parts of austenitic stainless-steel are connected by welding before expansion for making a rocket case. The ends of the case are made first by welding together at least one frusto-conical wall 13, Fig. 2, and a flat section 14 on each side of a cylindrical section 12 to form a hollow vessel. This is filled with liquid nitrogen and expanded by firing an explosive charge 17, the cylindrical section being held against expansion by rings 15 on each side of bars 19 welded to the vessel. The expansion operation also hardens the material by transforming the austenite to martensite, further improvement being possible by mantensitic strain hardening or low temperature ageing. Following this the vessel is cut into two halves and explosively expanded in a sizing die 21, Fig. 3, using a liquid such as water as a transmission medium. After removing the ring 15, an edge 48 of the vessel is machined and an opening 51, Fig. 4, cut in the end of one of the parts to form the top of a rocket casing. A lifting ring 55 permits installation of an expander ring 56 operated by an hydraulic cylinder 58 to align the edge 48 with an edge 50 on the second part 57 during circumferential welding by a machine 59. The second part and unexpanded neck on the first part are explosively expanded and sized in separate operations in a die 85, Fig. 6. The expanding charge 65 is mounted on a liner 64 and surrounded by a temporary shield 60 enclosing a space 69 into which liquid nitrogen is introduced to freeze water in a space 67 before the shield is removed. After inserting the workpiece in the die, liquid nitrogen is fed through a pipe 68 to the space between the workpiece and charge. Vapour flows upwards to a coverplate 74 and through a pipe 75 into a hollow constricting ring 77 from which it passes through holes 80 to the space surrounding the workpiece. The pipe 75 is disconnected from plate 74 before the charge is fired which is insufficient to impact the workpiece against the die. A balanced charge could be selected so as to limit expansion of the lower end of the second part 57 without the ring 77. The expanded sections are now raised from the die for positioning a sizing charge which expands the sections against the die using water as a transmission medium and, or before, an annular core of ice. A balanced sizing charge may be used without an external die. Further cylindrical sections may be added before the lower end of the case 18a<SP>1</SP>, Fig. 7 (not shown). In this operation, a top section 86 only of the die 85 is used which, during the welding stage, is spaced by bars (91) from the sizing die 21 carrying the lower section. The section 86 is now lowered to engage the die 21, Fig. 8, and an explosive charge is positioned on a body 104 of ice and having an ice-core 103, liquid nitrogen being used as the transmission medium. A further explosive core is used for sizing, using water as the transmission medium. Test cylinders were seam-welded, using an inert gas shielded tungsten arc process, the inside of the cylinders being purged by argon gas during welding of the outside seam, and the inner seam being welded with filler material cut from the parent metal. The strain hardening may be effected at ambient temperatures if the material is unstable at room temperature. The material may include the following, percentages by weight: c 0À05-0À11; Si 0À32- 0À77; S 0À007-0À023; mu 0À45-0À95; cr 15À5- 16-84; p 0À01-0À027; Ni 6À5-7À98.