GB2314519A

GB2314519A - Welding heavy duty drill pipes

Info

Publication number: GB2314519A
Application number: GB9713007A
Authority: GB
Inventors: Ulrich Katolla
Original assignee: KLEMM BOHRTECH; Ing G Klemm Bohrtechnik GmbH
Current assignee: KLEMM BOHRTECH; Ing G Klemm Bohrtechnik GmbH
Priority date: 1996-06-25
Filing date: 1997-06-19
Publication date: 1998-01-07
Also published as: GB9713007D0; IT1291386B1; ITMI971049A1; ITMI971049A0; DE19625301A1

Abstract

In welding a threaded sleeve (13) to a pipe (10). They each have their ends provided with chamfers (11, 14) forming a welding groove (15). Below the welding groove (15) there extends a lip (16). During welding, the groove (15) is filled with welding deposit (18), the material of the lip (16) being fused and forming a homogenous root of the seam together with the welding deposit.

Description

2314519 A method for producing beayy dull drill lpipes This invention

refers to a method of producing heavy duty drill pipes, in particular for rotary percussion drilling, wherein a thread is welded to a steel pipe.

Heavy duty drill pipes for ground and rock drilling have threads at both ends thereof to allow a plurality of pipes to be assembled to a train of drill pipes. Usually, the drill pipes are provided with inner threads at their ends. A so-called "double nipple" is used to connect two pipes, having an outer thread at each of its opposite ends, on which threads the inner thread of an adjacent pipe is screwed. Such double nipples are made of high-strength tempering steel (42 CrMo 4) and are subjected to a thermal surface treatment. Their production is rather costly. Also the drill pipes with double nipple connections are expensive, since they have to be made from high-quality steel (36 Mn 4).

Drill pipes for rotary impact drilling are subject to various stresses caused, on the one hand, by the rotation and, on the other hand, by being struck axially with heavy hydraulic hammers. Here, micro-fissures in the pipes often lead to pipe ruptures. It has been attempted to manufacture drill pipes with an end thread by welding a prefabricated threaded sleeve to a smooth pipe using friction welding. Generally, this requires preheating of the parts to be welded and a slow controlled cooling following the welding. However, it has been found that the drill pipes made by friction welding do not provide for a better durability. In particular, an axial offset of the threaded sleeve with respect to the pipe can occur and micro-fissures may be caused in the region of the connection. Further consideration should be given to the fact that the pipe and the threaded sleeve must be made of high-strength steel that is at the limit of weldability, a homogenous weld connection being hard to obtain with the friction welding method.

It is an object of the present invention to provide a method for producing heavy duty drill pipes that is highly economical to implement and yields high quality drill pipes.

2 The object is solved, according to the invention, with the features of claim 1.

In the method of the present invention, a threaded sleeve is welded to a pipe preferably made of a low-cost steel (ST 52.0). To this end, the pipe and the threaded sleeve are provided with chamfers and one of these members is further provided with an axially protruding lip below the chamfer, while the other member is provided with a recess receiving the lip. The pipe and the threaded sleeve are abutted such that the lip fills the recess and the chamfers form a V-shaped welding groove. Thereafter, an all-around welding along the welding groove is performed by inert gas arc welding, the welding groove being filled with a welding deposit. In doing so, the relatively thin lip us fused and melts together with the welding deposit to form a homogenous root of the seam. The seam has no joints or micro-fissures. The lip engaging the recess allows for an exact centering of the parts to join so that a perfect axial orientation is guaranteed. After the weld seam has been made, the drill pipe is finished. Due the welding deposit used in welding, no subsequent treatment of the welding is required.

The present method yields drill pipes that can take high dynamic loads, impact loads and tensile and bending stresses. The present method is particularly applicable to drill pipes for rotary impact drilling, and especially for pipes used in superposed drilling. The usual failures, such as ruptured roots in the weld, no longer occur.

Preferably, the lip is formed with a wall thickness of less than 1 mm, in particular 0.5 mm.

The following is a detailed description of one embodiment of the present invention made with reference to the accompanying drawings.

In the Figures 3 Fig. 1 is a longitudinal section of the abutment region of the pipe and the threaded sleeve before welding, Fig. 2 is an enlarged view of the detail II in Fig. 1, and Fig. 3 is a sectional view of the finished weld seam.

Fig. 1 illustrates the end portion of a pipe 10 of generally cylindrical shape. At the end face of the pipe 10, a chamfer 11 with a chamfer angle of 3 0' is provided. This chamfer does not extend to the inner surface of the pipe. It ends at an annular recess 12 formed on the inner side of the pipe.

Abutted against the pipe 10 is a threaded sleeve 13 having a thread (not illustrated) in the form of an outer and/or an inner thread. The tubular threaded sleeve 13 is prefabricated and also formed with a chamfer 14 of 30' at its end facing the pipe 10. Together, the two chamfers 11, 14 form a V-shaped welding groove 15 with an opening angle of 60'.

The root area of the chamfer 14 is prolonged by an annular lip 16 projecting axially from the threaded sleeve 13, the lip fitting into the recess 12 of the pipe 10 and filling the same. Thus, the apex of the welding groove 15 is radially spaced from the inner surface of the pipe.

In the abutment region of the pipe and the threaded sleeve, there is a flare 17 of the inner wall.

In the embodiment illustrated, the wall thickness a of the threaded sleeve and the pipe is 10 mm, the axial length b of the lip 16 is 1 mm and the thickness c of the lip 16 is 0. 5 nun.

4 The lip 16 of the threaded sleeve 13 is inserted into the pipe 10, the lip serving for centering and axial orientation.

Thereafter, welding is performed along the welding groove 15 using a welding wire, the welding groove 15 filling with welding deposit 18. This is illustrated in Fig. 3. The welding is done by inert gas arc welding using a welding wire which provides the welding deposit 18. Here, a pulsed welding current is employed. During welding, the lip 16 fuses so that the weld seam 19 forms a bell-shaped root 21 of a homogenous mass at the inner wall of the pipe. The width of the weld seam 19 widens from a constriction 22 both radially inward and radially outward, as evident from Figure 3. In the root area of the chamfers 11, 14, as well as at the lip 16, the materials of the pipe and the threaded sleeve melt together with the welding deposit to form a homogenous weld seam 19.

Preferably, the pipe 10 is made of ST 50.0. For example, the threaded sleeve 13 is made of tempering steel 42 CrMo 4.

In the welding operation, a welding wire of, e.g., 1.2 mm in diameter is used, having the following composition:

c 0,05% Ni 20% Cr 10% Mo 3% Nb 3% Stabilizers 5% Fe rest., The elements mentioned above may deviate by up to 10% from the values given above.

To obtain a deep root penetration and for thermal insulation, the welding deposit is welded using inert gas, composed of the following elements:

C02 8% 02 0,5% He 26,5% Ar rest.

The individual elements may also differ from the above values by up to 10%.

Using the above described welding technique, root ruptures at the weld are avoided, which ruptures quickly become the origin of a beginning destruction of the weld seam when high bending stresses are applied.

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Claims

1. A method for producing heavy duty drill pipes, in particular for rotary percussion drilling, wherein a threaded sleeve (13) is welded to a steel pipe (10), characterized in that said pipe (10) and said threaded sleeve (13) are provided with chamfers (11, 14) and are abutted against each other, the chamfers together forming a V-shaped welding groove (15), that said pipe (10) or said threaded sleeve (13) is formed with an axially projecting lip (16) bridging the bottom of said welding groove (15), and the other member being formed with a recess (12) fittingly receiving said lip (16), and that said welding groove (15) is filled with a welding deposit (18) by inert gas arc welding, the lip (16) being fused in the process.

2. The method of claim 1, characterized in that said lip (16) is formed with a wall thickness of less than 1 nim, preferably 0.5 nun, and a length of about 1 mm.

3. The method of claim 1 or 2, characterized in that said lip (16) is formed inunediately adjacent the inner surface (20) of said pipe (10) or said threaded sleeve (13).

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4.The method of one of claims 1 - 3, characterized in that a welding deposit (18) with the following composition is used, the respective percentages being allowed to differ by up to 1M c 0,05% Ni 20% Cr 10% Mo 3% Nb 3% Stabilizers 5% Fe rest.

5. The method of one of claims 1 - 4, characterized in that an inert gas with the following composition is used, the respective percentages being allowed to differ by up to 1M C02 8% 02 0,5% He 26,5% Ar rest.

6.A method for producing heavy duty drill pipes substantially as described herein with reference to the drawings.