Abstract: A plant for exploiting geothermal energy by circulating water through a geological formation (1) at a substantial depth below the earth surface (2), comprises at least one supply hole (3) leading from the surface (2) down to said formation (1) and at least one return hole (4) for transporting heated water from the formation to the surface. The supply and return holes (3, 4) are interconnected by a plurality of heat absorbing holes (5) which are spaced more than 50 m apart. The heat absorbing holes (5) have a total length of many kilometers but a relatively small diameter in the order of 10 cm. A method for designing the plant involving determining the dimensions of the heat transfer holes (5) is also disclosed.

Abstract: A method for heating pipes with closely spaced end portions that are to be joined by forge welding or the like. Two diametrically opposed contacts are attached to each end portion for supplying high frequency alternating current for resistance heating of the material in the respective end portions. The contacts for one of the pipes being located in close proximity to and substantially in the same axial plane as the contacts for the other pipe. The contacts for one of the pipes are arranged to form an angle (.alpha.) with juxtaposed contacts of the other pipe so that the projections of the juxtaposed contacts onto the axial plane intersect.

Abstract: A method for forge welding or the like of a first and a second metal part, wherein at least one joint is established between opposed bounding surfaces on the two parts to be joined, and wherein preferably a reducing gas is passed through the joint or joints before the parts are pressed together. In order to make the weld less sensitive to remaining oxides, the bounding surfaces are provided with generally matching corrugations of somewhat different height.

Abstract: Arrangement in connection with induction butt-welding of the aubstantially pipe- or bolt-shaped elements of metal, which are provided close to each other along substantially the same center axis, and which at their welding edges define a narrow gap or joint which are kept approximately constant during the heating phase. For the purpose of achieving an electromagnetic field which can be guided into the area of the joint for rendering a concentrated heating area at the welding edges, a combination of a coil provided around the narrow gap and adapted for being subjected to a voltage in the frequency range of approximately 50-5000 Hz, and a cover of ferro-magnetic material provided around the coil and serving to guide the electromagnetic field to the area of the welding joint.

Abstract: In a method for heating metal elements (1,2) which are to be joined, for example by forge welding, there is used a high frequency resistance heating. The elements are provided with surfaces to be welded and are positioned so that said surfaces constituted a narrow gap (3). The current is conducted from a high frequency current source (11) through a contact (9) into one of the elements (1), wherefrom the current follows the material close to the gap surface (4) and to the opposite side of the element, where the current flows via further contacts (8,9) and a conductor (10) to the other element (2). From here the current follows the other gap surface (5) to another contact (7) and the current source (11). The current will follow a path close to the gap surfaces since these surfaces will give the path of smallest total impedance, the current thereby establishing a narrow and efficient heating zone in the vicinity of said gap surfaces.

Abstract: A method for joining thin-walled tubular parts (1, 2) of metal by forge/diffusion welding comprising establishing a joint (3) between opposed bounding surfaces (4, 5), the joint having increasing height from one side (7) to the other. During heating of the parts the joint (3) is supplied with an inert or reducing flushing gas, for instance hydrogen, until the oxides are removed from the joint surfaces (4, 5). By subsequently pressing the parts together, complete forge/diffusion welding is obtained. It is also suggested to reduce the cross-section of the parts excentrically in the joint area and press the parts out to their initial cross-section during the forge/diffusion welding. A packer (8) is used to close the joint (3) on the side where the distance between the parts (1, 2) is the greatest. Means (10, 11) are shown for performing the welding under water.

Abstract: A method for joining parts of metal by diffusion welding comprises initially the establishing of a joint between the opposed bounding surfaces, the joint having generally increasing height from the periphery towards the middle. The joint is provided with a connection to an external source for flushing gas and a vacuum source. During the preliminary heating and pressing together of the parts the joint is supplied with an inert for reducing flushing gas, e.g., hydrogen, until the joint by diffusion welding is closed along its periphery. Thereafter, a vacuum may be pumped in the joint, where upon further heating, quick compression and a certain holding time provide complete diffusion welding of the parts. It is also suggested to reduce the cross-section of the parts in the joint area and press these out to their original cross-section during the diffusion welding.

Abstract: A power plant for exploitation of the temperature difference between different water layers in a pelagic area (2), comprising a closed system which is filled with ethane which is both in the liquid and vapor phases. The system comprises two heat exchanging apparatuses (13, 9) which are in fluid communication with each other, of which the first (13) supplies heat to the ethane by means of heat exchange with water from a relatively warmer water layer, while the other (9) removes heat from the ethane by means of heat exchange with water from a colder water layer, whereby a difference in pressure is created in the system which is utilized to take energy out of the system. In order to make the system large enough and the ethane pressure high enough to give a reasonable power yield, the heat exchanging apparatuses are placed in respective chambers (5, 4) which are comprised by cavities in solid or consolidated rock (1).

Abstract: The present invention relates to a joint for trusses, preferably trusses where the force transmitting members mainly consist of tubes having relatively large diameters.