End piece of drill pipe, drill pipe assembly and method

Abstract

An end piece, a drill pipe assembly and method is provided. The drill pipe assembly is for rotary drilling and DTH drilling and includes a drill pipe provided with end pieces at its opposite ends. For the mounting of the end pieces a shrink fit and welding is implemented. For improving the shrink fit, the contact surfaces between the components are tapered.

1 . An end piece of a drill pipe for a rotary or DTH drilling rig, the end piece comprising:
 an elongated tubular piece: having an outer surface and an inner surface;   a first end provided with a first coupling means including threaded surfaces arranged for thread mounting with other drill components; and   an opposite second end provided with second coupling means arranged for coupling the end piece to the drill pipe by means of a shrink fit, wherein the second coupling means include a radial outwardly facing first contact surface extending a first axial distance from the second end towards the first end, and wherein the first contact surface has a tapered configuration.   
     
     
         2 . The end piece as claimed in  claim 1 , wherein an angle of the tapered first contact surface is 0.2-12°. 
     
     
         3 . The end piece as claimed in  claim 2 , wherein the angle of the tapered first contact surface is 1-6°. 
     
     
         4 . The end piece as claimed in  claim 1 , wherein a length of the first axial distance is 75-160 mm. 
     
     
         5 . The end piece as claimed in  claim 1 , wherein a length of the first axial distance of the tapered first contact surface is defined by a stop surface being orientated perpendicularly in relation to a longitudinal axis of the end piece. 
     
     
         6 . The end piece as claimed in  claim 1 , wherein at the second end of the end piece there is also a radial inner surface extending an axial distance from the second end towards the first end and having a tapered configuration. 
     
     
         7 . The end piece as claimed in  claim 1 , wherein an outer surface of the end piece is provided with at least one discard indicator being a recess having a predetermined depth. 
     
     
         8 . A drill pipe assembly for rotary or DTH drilling comprising:
 a drill pipe having opposed ends and an inside socket portion at each end of the drill pipe, the inside socket portions having a contact surface; and   an end piece according to  claim 1  mounted fixedly to each opposed end of the drill pipe, wherein the end pieces each include a male portion with a second coupling means outwardly facing first contact surface and being arranged to be inserted into inside socket portions at the ends of the drill pipe, wherein the end pieces are connected to the ends of the dill pipe by means of shrink fits based on a differences between the respective male socket portions and inside socket portions, and wherein mating radial first contact surface of the male portions and the contact surface of the socket portions have tapered configurations.   
     
     
         9 . The drill pipe assembly as claimed in  claim 8 , wherein a magnitude of the shrink fit is 0.1-0.8 mm. 
     
     
         10 . The drill pipe assembly as claimed in  claim 8 , wherein a magnitude of the shrink fit is 0.2-0.6 mm. 
     
     
         11 . The drill pipe assembly as claimed in  claim 8 , further comprising weld joints between the end pieces and the drill tube arranged for providing additional fastening. 
     
     
         12 . A method of forming a drill pipe assembly to be used in a rock drilling rig, wherein the method comprises:
 mounting end pieces to opposite ends of a tubular drill pipe;   providing first ends of the end pieces with first coupling means comprising thread surfaces for thread mounting;   providing opposite second ends of the end pieces with truncated cones wherein radial outer surfaces of the truncated cones form first contact surfaces;   forming socket parts to both ends of the drill pipe for receiving the truncated cones and being provided with second contact surfaces;   heating the ends of the drill pipe at the socket parts to expand diameters of the second contact surfaces by means of thermal expansion;   pushing the truncated cones inside the thermally expanded socket parts;   allowing the heated socket parts to cool and shrink whereby shrink fits are formed between the first and second contact surfaces;   securing the mountings between the drill pipe and the end pieces by welding; and   providing the mating first and second connecting surfaces with tapered shapes.