GB2164358A - Method for the surface hardening of drill rod couplings - Google Patents

Abstract

A method for surface-hardening a facial band (F) of the female coupling (6) of a steel drill rod, said band lying between the threaded zone (7) of the coupling and the tapered zone (5) which joins the coupling to the cylindrical rod body (1) comprises cleaning said band by brushing and/or sandblasting, inductively preheating the band and finally raising a surface film layer of said band to austenitizing temperature by means of a laser beam. <IMAGE>

Description

SPECIFICATION Improved method for the surface hardening or drill rod couplings, and the rods thus obtained This invention relates to an improved method which enables the couplings of drill rods to be effectively surface- hardened without producing abrasive roughness.

The invention also relates to the drill rod thus obtained. In drilling wells, it is known to use drill bits disposed at the lower end of a series of drill rods which are joined together in series to form a given length.

Each of said rods consequently consists of a cylindrical steel body provided at its respective ends with a male coupling comprising an external thread and a female coupling comprising a corresponding internal thread.

As the outer surfaces of the rod couplings necessarily project from the rod body to which they are joined by tapers, these surfaces are the first to come into contact with the inner surface of the well and are thus subject to rubbing against the earth, or against the casing where this is present in the well.

Prolonged rotation of the drill inside the well therefore produces continuous wear of the rod coupling by abrasion, this intolerably reducing the life of the rod, which because of its high cost considerably affects the overall economy of the drilling operation.

In the present state of the art, the aforesaid drawback is generally obviated by surface-hardening the rod female coupling, this being the more critical in terms of loss of thickness by abrasion.

More specifically, only a facial band of said coupling lying between the zone comprising the thread and the tapered zone, and being of about 60-80 mm in width, is hardened because the threaded zone cannot be touched as a certain softness has to be maintained in order to allow reliable gripping by the operating keys, and the tapered zone does not require hardening.

The hardening method currently used consists of applying a hardener such as tungsten carbide reduced to minute particles of irregular or spherical shape to the facial band in question by fusion. In this respect, by virtue of the fusion the excipient material with which the tungsten is mixed analganates with the molten steel of the coupling surface, and the hardening material thus remains incorporated in the outer surface of the coupling face.

This known method is not however without serious drawbacks, in that even though the hardening elements are minute in size, the surface obtained in this manner is indeed of greater hardness but is also strongly abrasive, and damages the casing of the drilled well against which it acts.

As only a minimum part of the drilled well is normally free of casing, and thus most of the well is effectively cased and therefore subjected to the damaging action of the hardened coupling, it is apparent that this latter drawback is even more serious than the previously stated drawback in that whereas formerly there was excessive wear of the rods which, after a very short life, were no longer usable without damaging the well, the coupling are now properly safeguarded giving a relatively long rod life, but the well casing is irreparably damaged, and as this is a permanent element of the well it cannot tolerate any breakage or wear of any kind.

The object of the present invention is to obviate the aforesaid drawbacks by providing a method for surface- hardening said facial band of the female coupling of drill rods, which creates no abrasive roughness and is therefore not damaging to the drilled well casing. This is attained substantially by using coherent radiation emitted by CO2 generators, also known as the laser create a flow of energy over said band of the coupling to be hardened, such as to heat it not to the melting temperature, but to heat only a surface film layer, of thickness of the order of 1 mm, of said band to austenitizing temperature.In this respect, because of the limited quantity of heat required for this purpose this heat is transferred by conduction to the underlying colder layers so rapidly that the thus treated surface layer of the band passes from austenitic structure to martensitic structure and thus becomes very hard (hardened steel).

The advantages of such a type of hardening are immediately apparent, in terms of the result obtained, the practicality of implementing it, and its cost. In this respect, exceptional hardness is obtained precisely at the specific required points because the laser beam consists of electromagnetic radiation which is easily controllable and directable in accordance with optical laws. On the other hand, there is no need for costly hardening material such as tungsten carbide, no7vfor the complicated equipment which would be necessary for grinding, melting and applying said materials, as the treatment is now effected by simple relative motion between the coupling and the focused beam, as the laser beam does not operate under vacuum and does not generate combustion products or gases as happens when applying tungsten carbide.

It has also been found that for the treatment to be most effective, that facial band of the rod female coupling which is to be surface-hardened must be cleaned by brushing or sandblasting before treatment, in order to facilitate absorption of the laser beam energy, and should also be inductively preheated to prevent the formation of cracks, from which fractures can be triggered, in the transition zone between the treated surface layer and the interior of the coupling face, which is essentially of uncharged structure.

Thus, the method for surface-hardening a facial band of the female coupling of steel drill rods, where said band lies between the zone comprising the internal thread of the coupling and the tapered zone which joins the coupling to the cylindrical rod body, is characterised according to the present invention by comprising the following stages: cleaning said band by brushing and/or sandblasting, inductively pre-heating said band, and finally raising a surface film layer of said band having a thick ness of the order of 1 mm to the austenitizing temperature by means of an incident energy flow generated by coherent radiation emitted by a CO2 laser generator.

Finally, as said thus hardened facial band of the drill rod female coupling is not only very hard but is also very fragile, in order to reduce the danger of crack formation to a minimum and thus make the coupling more resistant to the various operational stresses, according to a preferred embodiment of the present invention the hardening of said band according to the said method is not implemented over the entire band, but over parallel alternate strips so as to compensate the very low elasticity of the hardened zones or strips by the unchanged elasticity of the unhardened intermediate strips.

The invention is described in detail hereinafter with reference to the accompanying drawing which illustrates a preferred embodiment thereof by way of non-limiting example in that technical or constructional modifications can be made thereto without leaving the scope of the present invention.

On said drawing the Figure shows a partly sectional view of a drill rod constructed in accordance with the invention.

In the Figure, the reference numeral 1 indicates the cylindrical steel body of a drill rod, the lower end of which is joined by way of the tapered zone 2 to a male coupling 3 provided with an external thread 4, and the upper end of which is joined by way of the tapered zone 5 to a female coupling 6 provided with an internal thread 7.

The facial band F of said female coupling 6 lying between the zone comprising the internal thread 7 and the tapered joining zone 5 is hardened along the alternate parallel strips 81 (three strips in the Figure) by means of a laser beam which raises the temperature of a film layer of said strips 81 having a thickness of the order of 1 mm to austenizing temperature.

Prior to the laser action, said strips 81 are cleaned by brushing and/or sandb[asting and are then inductively preheated, the laser treatment of the strips being implemented with relative motion between the coupling and laser beam obtained by known means which enable the coupling to be suitably rotated and translated along its axis while keeping the laser beam at rest, or which keep the coupling at rest and cause the laser beam to make corresponding movements by suitable rotary and translational movements of its reflecting surface.

Claims (5)

1. A method for surface-hardening a facial band of a female coupling of a steel drill rod, said band lying between a zone comprising an internal thread of the coupling and a tapered zone which joins the coupling to a cylindrical body of the drill rod, the method comprising the steps of cleaning said face by brushing and/or sandblasting, inductively preheating said band, and raising a surface film layer of said band to the autanitizing temperature by means of an incident energy flow generated by coherent radiation emitted by a CO2 laser generator.

2. A method according to claim 1, wherein said band has a thickness of the order of imam.

3. A steel drill rod comprising a cylindrical body provided at its ends with, respectively, a male coupling provided with an external thread and a female coupling provided with a corresponding internal thread, said coupling being joined to said body by way of tapered joining zones, wherein the facial band of said female coupling lying between the zone comprising said internal thread of the female coupling and said tapered joining zone comprises alternate parallel strips hardened by a method according to claim 1 or 2.

4. A method for the surface hardening of a drill rod coupling substantially as described herein.

5. A drill rod substantially as described and illustrated herein.