EP2050922B1

EP2050922B1 - Thread for roto-percussion drill pipe

Info

Publication number: EP2050922B1
Application number: EP08166631.5A
Authority: EP
Inventors: Jamie Thompson
Original assignee: Roggan Investments Ltd
Current assignee: Roggan Investments Ltd
Priority date: 2007-10-16
Filing date: 2008-10-15
Publication date: 2023-01-11
Anticipated expiration: 2028-10-15
Also published as: ITMI20071992A1; ES2937164T3; EP2050922A2; EP2050922A3

Description

The present invention relates to a roto-percussion pipe.
In the known art, roto-percussion pipes are formed with a tubular portion, at the end of which a male thread and a female thread are present. By connecting together a plurality of pipes using these threads, drill strings of any desired length can be obtained.
In practice, the first end of a first pipe is fixed to a drilling head. The second end of the first pipe is coupled to a roto-percussion drill bit which drills the ground. When nearly all of the first pipe has advanced into the ground, the drill bit is disconnected from the second end, and the first end of a second pipe is screwed into this second end. The second end of the second pipe is connected to the drill bit and drilling continues. When nearly all of the second pipe has advanced, the aforedescribed process is repeated with a third pipe and so on, until the required drilling length has been reached. Known pipes present standard two-start threads. This causes considerable problems in that often, during a pipe adding operation, the thread seizes, making the drill string unusable.
Document DE 19803304 A1 discloses a roto-percussion pipe according to the preamble of claim 1, wherein the pipe comprises a tubular portion having at its ends a female coupling, carrying a female thread, and a male coupling, carrying a male thread, and wherein these threads are three-starts threads.
The object of the present invention is to provide a roto-percussion pipe which overcomes the drawback of the known art by minimizing the danger of seizure during the connection of a new pipe or the disconnection of a pipe from the drill bit.
This object is attained by a roto-percussion pipe in accordance with the technical teachings of the accompanying claims.
Further characteristics and advantages of the invention will be apparent from the description of a preferred but non-exclusive embodiment of the roto-percussion pipe illustrated by way of non-limiting example in the accompanying drawings, in which:

Figure 1 is a side view of the pipe of the present invention;
Figure 2 is a section through a female coupling of the pipe of Figure 1, the coupling being shown separated from the pipe;
Figure 3 is an enlarged section through a male thread provided on a male coupling of the pipe of Figure 1;
Figure 4 is an enlarged section through a detail showing a first weld seam joining together the couplings and the tubular portion of the pipe of Figure 1;
Figure 5 is an enlarged section through a detail showing a second weld seam joining together the couplings and the tubular portion of the pipe of Figure 1;
Figure 6 is a partial section through the pipe of Figure 1 during assembly, before the welds between the tubular portion and the couplings have been made; and
Figure 7 is a partial section through the pipe of Figure 1, showing a stage in the welding carried out on an automatic machine.

With reference to said figures, these show a roto-percussion pipe indicated overall by the reference numeral 1.
The pipe 1 presents a tubular portion 2 constructed of N80 special steel, which is of substantially tubular shape, internally hollow and of circular plan. To one end of the tubular portion 2 a female coupling 3 is welded having a female thread best visible in Figure 2. The thread in question has a 30 mm pitch and presents three starts. In the entry portion 3A of the thread the commencement of the thread spiral has been removed to form a bevel which facilitates the connection between the male part and a further pipe.
To one end of the tubular portion a male coupling 4 is welded presenting a male thread best visible in Figure 3. The thread in question has a 30 mm pitch and presents three starts, and is suitable for connection to the female thread 3. It advantageously has a fillet radius R of 4 mm (see Figure 3). In the entry portion 4A of the thread the commencement of the thread spiral has been removed to form a bevel which facilitates the connection with the female thread.
Both the couplings are made of 42 Cr Mo 4 steel, before being welded to the tubular portion they being subjected to surface hardening treatment, preferably nitriding. The portion at which the weld is to be made is then removed mechanically to provide the welding machine with a non-treated surface presenting mechanical characteristics suitable for the subsequent welding.
Centering profiles are created on the end portions 20 of the tubular portion and on the joining surfaces 30, 40 to facilitate coaxial mounting of the tubular portions and couplings.
During assembly the tubular portion 2 is positioned between the male coupling 2 and female coupling 3, and a tie bar 10 is inserted through the pipe interior. Two plates are rested against the couplings, and the tie bar is tightened using adjustment handles. Manual spot welds (3-4) are then made between the couplings and the tubular portion 2, to maintain the pipe assembled before its final automatic welding.
The tie bar is then loosened and the pipe is passed to the wire welding machine 15 (Figure 7). The pipe is gripped within the welder headpiece 14 and two automatic weld passes are carried out by the head 18 positioned to straddle the tubular portion 2 and the female coupling 3. The first pass forms a first weld seam (Figure 4), with the second pass completely filling the welding region (Figure 5). The automatic welding is carried out on a wire welding machine in a protected atmosphere using an AISI 312 stainless steel welding wire.
The welding head 18 is then moved to straddle the male coupling 4 and the tubular portion 2, another weld then being made.
Advantageously the presence of a 3-start thread enables a pipe inserted into one already used for drilling to be maintained coaxial, so preventing seizure. In addition, the nitriding treatment considerably lengthens the life of the pipes in question.

Claims

A roto-percussion pipe (1), comprising a tubular portion (2) having at its ends a female coupling (3) carrying a female thread and a male coupling (4) carrying a male thread, said male coupling (4) and female coupling (3) enabling the pipe (1) to be connected to other pipes identical therewith to form a roto-percussion drill string of the required length, said threads having at least three starts, the pipe (1) being characterised in that said tubular portion (2) and said couplings (3; 4) are formed as separate pieces, said couplings (3; 4) being welded to said tubular portion (2), wherein said couplings (3; 4) are hardened on their surfaces, a surface hardening treatment being carried out on said couplings (3; 4) before being welded to said tubular portion (2), the hardened portion of the surface of the couplings' portions at which the weld is to be made being removed mechanically subsequent to said treatment to provide the welding machine with a non-treated surface presenting mechanical characteristics suitable for the subsequent welding, wherein said tubular portion (2) is provided with end portions (20), centering profiles are created on the end portions (20) of the tubular portion (2) and on joining surfaces (30, 40) of said couplings (3, 4) to facilitate coaxial mounting of said tubular portion (2) and said couplings (3; 4), wherein said tubular portion (2) is made of N80 special steel that is different from 42 Cr Mo 4 steel with which said couplings (3; 4) are made of, and wherein a weld seam made of an AISI 312 stainless steel welding wire is formed between said tubular portion (2) and said couplings (3; 4).
A pipe (1) as claimed in claim 1, characterised in that said surface hardening treatment is nitriding.
A pipe (1) as claimed in claim 1, characterised in that the commencement of the thread spiral is removed to facilitate engagement.
A pipe (1) as claimed in claim 1, characterised in that said couplings (3; 4) present engagement bevels to facilitate mutual centering.
A pipe (1) as claimed in claim 1, characterised in that said thread has a 30 mm pitch.
A pipe (1) as claimed in claim 1, characterised in that the thread presents a fillet radius R of 4 mm.