Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~2~ i;4
CASE ~081
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 ~oined together in
series to form a given length.
Each of said rods consequently consists of a cylindrical steel body
; lo 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 pro~ect 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 couplings by abrasion1 this intolerably
reducing the life of the rod, which because of its high cost conside-
rably 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
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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 amalgamates 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 draubacks, in that
ever. though the hardening elements are ~inute in size, the surface
- obtained in this manner is indeed of greater hardness but is also
stron~ly 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 couplings 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 ob~ect of the present invention is to obviate the aforesaid
drawbacks by providing a method for surface-hardening said facial
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band of the female coupling of drill rods, which creates no abrasive
roughness and is therefore not damaging to the drilled well casing.
Th$s ls attained substantially by using coherent radiation emitted
by CO2 generators, also known as the laser beam, to 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
; 10 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,
asd 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 materials such as tungsten
carbide, nor for the complicated equipment which would be necessary
for grinding, melting and &pplying 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-
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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,
~hich is essentially of unchanged 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 thickness of the order of 1 mm to the austenitizin~
; 15 temperature by means of an incident energy flow generated by coherent
; radiation emitted by a C02 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 paralle] 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
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thereof by way of non-limiting example in that technical or construc-
tional 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 ~ indicates the cylindrical steel
body of a drill rod, the lower end of wh~ch is ~oined 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 alterr,ate parallel strips 8i (three strips in the
figure) by means of a laser beam which raises the temperature of a
film layer of said strips 8i having a thickness of the order of 1 mm
to austenizing temperature.
Prior to the laser action, said strips 8i are cleaned by brushing and
or sandblasting and are then inductively preheated, the laser
treatment of the strips being implemented with relati~e motion between
; 20 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 surfaces.
