Bohrlochkopfstruktur

The improved wellhead structure of the present invention includes a casing or tubing string (10) which is sealed to the housing (18) without the aid of elastomeric seals and an internal bushing (14) to assist in providing the tight gripping and sealing engagement between the string and the housing. The structure provides a substantial inner diameter which is unrestricted unless landing shoulder is included in the structure. Also, the internal bushing used with the cold forging of the string into the housing recess improves the gripping and sealing engagement therebetween. In one form the bushing (14) includes a series of external projections which alternate with the gripping and sealing projections within the housing recess and in another form includes a resilient annulus (42) between the interior of the bushing and the string to ensure the uniform application of pressure against the interior of the string. In still another form an internal landing shoulder is cold forged into tight engagement with the interior of the housing which allows full bore operations to be carried through the housing until the landing shoulder is to be installed. Also provided is a wellhead structure with a tieback structure in which the upper end of the casing is cold forged into the interior of a hanger while the casing is supported on slips.