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Патент USA US2405859

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' Aug. 13, _1.946.A
H. E. sQMEs>
« 2,405,859
¿Filed Deo. 20. 1941
Patented Aug. 13, 194s
Howard E. Somes, Detroit, Mich., assignor, by
mesne assignments, to Edward G. Budd Manu
facturing Company, Philadelphia, Pa., a, cor
poration of Pennsylvania
Application December 20, 1941, Serial N0. 423,739
2 Claims. (Cl. 166-4)
This invention relates to tubular articles and
In the drawing which illustrates a suitable em
more particularly to an axial assemblage of tu
bular articles such for example, as oil well cas
bodiment of the invention:
tion of a casing section undergoing a heat treat
An axial assemblage of tubular articles is fre
quently subjected to unusual stress conditions,
ing operation; and
one of the most common examples of which is an
Figure 1 shows a fragmentary sectional -por
Figure 2 is a fragmentary elevational view of
an oil well casing string.
I attain the objects of the present invention
oil well casing. An oil well casing, commonly
by employing certain heat treating operations to
known as a string, is comprised of a plurality of
steel tubes axially connected together and ex 10 provide the casing sections with an internal an»
nular zone or layer extending from end to end
tending many thousands of feet into the earth,
it being not uncommon to set oil well casings to
and to create within the inner and outer zones
certain predetermined residual stress conditions
v depths of between 9,000 and 12,000 feet. In a
few instances, casings have been set to a depth
which combine with the hardened zone to in
of 18,000 feet. The casing string is suspended at
crease the strength of the casing sections, the
sections to be used for the upper portion of `the
its top and frequently is sealed at its lower end
casing string being provided with stress condi
with concrete or other suitable material, and is
supported at such lower end. Due to the great
tions different from the stress conditions existing
in the casing sections employed for the lowe11 por
weight of the string, at least the upper sections
tion of the casing string.
thereof are subjected to severe tensile stresses
The casing sections are ñrst subjected to a
acting in an axial direction especially during in
heat treating operation similar to that described
stallation when the string is being supported from
the top. At the bottom of the string, many of
in my Patent No. 2,281,331, April 28, 1942, where
in there is disclosed a method and apparatus for
the lower casing sections are subjected to axial
compressive stresses which arise out 0f the fact 25 progressively hardening:A an internal layer of a
that the elongation and more particularly the
tubular member by- generating heat in the in
ternal layer through magnetically induced heat
weight of the upper sections imposes an axial
ing currents.
compression load on such lower sections especially
In accordance with the method disclosed in my
after installation. In addition, the hydro-static
pressure existing externally of the lower casing 30 copending application aforesaid, an electro-mag
netic induction heating head “H” and a quench
sections exerts severe external pressures radially
head “Q” are arranged in coaxial relation with
against the Walls thereof which set up compres
the casing section to undergo the heat treating
sive stresses in the casing wall tending to col
operation and in such manner that relative axial
lapse the same.
Oil well casings are being set deeper and 35 movement can be effected between the casing sec
tion Il on the one hand and the heatingv and
deeper and this means that the tensile stresses in
quenching heads on the other hand while prefer
the upper sections and the compressive stresses
ably effecting relative rotation. The coil I2 of
in the lower sections are becoming greater and
the heating head is connected to a high frequency
greater, it being well known that the hydrostatic
pressures increase as the depth of the casing set 40 source of alternating current and is provided with
a laminated iron core i3 threading its center in
ting increases.
order to assist in the concentration of heating
From the foregoing it is clear that whereas ten
energy at a high rate inthe internal layer or
sile strength is of greater importance at the top
of the string, compressive strength is of greater
Zone which is to be hardened. The quench head
and major importance at the bottom of the 45 Q is preferably provided wtih an annular oriñce
Q-lß arranged as closely as possible to the trail
string. The aim, therefore, of the present in
ing end of the coil l2 to discharge an annular
vention is to provide an oil well casing string or
stream of quenching medium against the heated
similar structure of improved construction where
internal surface.
in the casing sections forming the upper part
The construction of the heating and quenching
of the string and those forming the lower part r
heads H and Q, respectively, may be substantially
of the string, respectively, with respect to a
the same as that disclosed in said copending ap
standard oil well casing of the same dimensions
plication and of course may be of any other suit
and composition, have increased resistance to
able design and construction, such as shown in
axial tensile failure and increased resistance to
Figure 1, and capable of producing the same
collapse from the exertion of axial and radial
compressive forces.
rapid heating and quenching results.
With the above and other objects in view, the
present invention consists of certain features to
be hereinafter described with reference to the
The heat is generated annularly at a desired
shallow depth in the internal zone within a period
of a very few seconds and this heated 'zone is
accompanying drawing, and then claimed.
immediately quenched before any of the heat
generated in the same can drift to the metal of
the outer zone in. any consequential amount, thus
providing an inner hardened layer I4 of metal
and an outer unhardened or less hard annular
layer I5 of metal.
By reason of the rapid generation of heat in
the inner layer I4 and the rapid quenching of
the same, a state of trapped stresses is set up>
in which the inner hardened layer I4» is placed
under residual compression and the outer less
hard layer I5 is placed under residual tension,
that is, when the tubular structure is under an
unloaded condition. The outer layer may be
placed under a state of residual tension in an
amount approximately that of its yield strength. ,
It is well known, of course, that the tensile
strength of a layer of metal is increased by hard
ening the same and that this increase in strength
increases with the hardness.
For the lower sections B of the casing string
illustrated in Figure 2 wherein compressive
strength is of major importance the casing sec
tions treated in the manner just described are
employed, these sections being provided with an
outer unhardened layer I5 under residual ten
sion and an internal layer i4 under residual
compression and hardened to such hardness as
to increase its ultimate strength to a strength
manifoldly greater than that of the unhardened
layer I5» which, for example, may be three times
thatof the unhardened layer. For example, the
ultimate strength of a metal hardened to 60
section is placed under axial compressive load
ing the external unhardened layer I5 being under
considerable tension in opposition to the com
pression stress of the internal layer I4 assists the
section in resisting axial compressive loading by
the amount of the residual tension stress, since
the axial loading must ñrst neutralize this re
sidual tension stress.
It is obvious that in such heat treated cas
ing sections B in which the internal layer is hard
ened the yield point or yield stress to which it
may be carried exceeds the yield strength of the
unhardened material and therefore, the internal
layer may, when the casing section is subjected
to an axial compressive loading, be stressed to a
much higher point than the outer layer and still
remain within the yield point of the material.
For the casing sections A in the upper portion
of the casing string A--B wherein tensile strength
is of greater importance, the present invention
contemplates the embodiment of casing sections
having the internal annular layer I4 hardened
substantially the same as in the lower sections B
but in which the internal layer is placed under
a. state of residual tension and
l5 is placed under a state of
sion, that is, when the casing
unloaded condition.
In such a structure, it will
the external layer
residual compres
sections are in an
thus appear that
with the metal of the internal hardened layer
I4 having a tensile strength far in excess of the
strength of the external unhardened layer I5 and
at the same time being under tension while the
on the Rockwell C scale may be as high as 311,000
outer layer is under compression, an axial ten~
pounds perv square inch whereas the same metal
sion load exerted on the casing section will ñrst
prior to hardening might have had an ultimate
neutralize the compressive stress in the outer
strength of 93,000 pounds per square inch as
layer and at the same time increase the tension
suming it had an original hardness of Rockwell
stress of the internal hardened layer I 4. The
C 10; This strength of 93,000 pounds per square
metal of this internal layer due to its hardness
inch is considerably above the yield strength
which would probably be in the order of 60,000 40 however, is of manifoldly greater strength than
pounds per square inch.
the metal of the external unhardened layer. Con
sequently, the metal of the hardened internal
Assuming for example, that the yield strength
layer and the metal of the external layer combine
of the unhardened layer of the casing section is
and assist each other in resisting axial tensile
two-thirds of the ultimate strength and that the
loading and thus the axial tensile strength of
outer layer is under a residual tension substan
tially equal to its yield strength, it will thus ap
the casing section is increased, the initial assist
ance of the external layer being the amount of
pear that an external radial load such as arises
its residual or> trapped compression stress.
from the hydro-static pressures existing exter
In order to bring about the stress reversal in
nally of the lower sections of the casing strength
changing the residual stress of the external layer
must ñrst neutralize the tension stress in outer
I5 from a tension to a compression stress con
layer I5, this, in the present case, being an
dition and of the internal layer I4 from a corn
amount equal to two-thirds of the ultimate
pression-to a tension stress condition, the internal
strength of the outer layer. It thus will be seen
layer I4 is expanded, but not beyond its elastic
that the outer layer is still capable of withstand
limit, an amount suiiicient to expand or stretch
ing a compressive load equal substantially to its
the metal of the external layer beyond its yield
ultimate strength, and therefore, that since the
point whereby to upset the same. Upon con
strength of the hardened layer is in the order
traction of the internal layer the external layer is
of three times that of the unhardened layer, the
placed under compression and the internal layer,
two layers combine and assist each other in re
due to the resistance of the external layer to com
sisting the compressive loading, at least‘to the
pression, isv placed under tension.
extent of the strength of the outer unhardened
It must> be borne in-mind, however, that the
layer, Actually, however, the casing will with
total strength 0f the hardened layer must be
stand an external loading greater than the sum
greater than the total strength of the unhardened
of two-thirds the ultimate strength (the residual
layer so that the upsetting of the external layer
tension stress) of the outer layer I5V and the
is accomplished before the internal layer reaches
strength of such loading because of the increased
its elastic limit.
strength of the internal layer I4. It thus is seen
The reversed stress may be brought about me
that the resistance of the» casing section to col
chanically or by longitudinally stressing the same
lapse is materially increased.
through the application of opposed tension-exert
It will, of course, be obvious that the axial com
ing forces at its ends, or by closely confining the
pressive strength of such casing section will be
peripheral surface thereof throughout its length
materially increased by the treatment described.
and subjecting the same to high internal hy
The residual tension stress of the external layer
draulic pressure. The stress reversal also may
exerts itself not only circumferentially but also
be brought'about in accordance with the disclo
axially of the section and consequently, when the
sure of my Patent No. 2,315,558, granted April 6,
1943, wherein I proposed to thermally expand the
internal layer I4, through the use of the electro
magnetic induction heating head l-l shown in»
strength, and the lower sections, wherein axial
and radial compressive stress is of major im
portance, have increased axial and circumferen
tial compressive strength, as compared to sec
tions of the same size and composition. Other
advantages, oi course, are manifold, particularly
the temperature of the internal hardened layer
in the reduction in weight and saving in cost.
to the .desired temperature, for example, such as
The number of sections at the upper and lower
400 degrees Fahrenheit. In applying the heat to
portions of the casing to be treated in accordance
this internal layer almost instantaneo-usly and
before any consequential heat may escapethere
with the disclosures herein may, of course, vary
depending upon the depth of the well, which as
from to the external layer l5, the internal layer
is well understood is usually determinable in ad
which was initially under compression is forced
vance to drilling the well. The intermediate sec
to expand because of the increase in compression
due to thermal expansion resulting from the heat
tions may be untreated. However, in any event,
generated therein and the consequential tempera 15 the portions of all the sections may be hardened
under the threaded end zones to increase the
ture rise in the internal layer. The additional
strength of the joints to compensate for loss in
compressive stress developed in the internal hard
Figure 1, by substantially instantaneously raising
ened layer through the rapid heating thereof will
strength resulting from the cutting of the threads.
The production of hardened zones underlying the
be suirlcient to stress the cold external hardened
layer beyond its elastic limit so that it will take 20 threads 2s is preferably accomplished in the
a permanent set.
same manner as that outlined in connection with
the portions forming the lower casing sections,
In practice, tubular members treated in the
wherein high collapse strength is desired.
manner set forth will be found to have had their
axial internal diameter enlarged slightly through
Although the invention has been illustrated
and described in general in connection with a
this treatment, and too because the external layer
has been given a permanent setting and stressed
speciiic embodiment, it is to be understood that
beyond its yield point allowing the internal layer
the same is not limited thereto but may be prac
formerly under compression to expand, the heat,
ticed in various forms and ways. As many
changes in the procedure and in the structure
however, being such that the inner layer is not
expanded beyond its yield point. No quenching 30 evolved therefrom may be made without depart
need be resorted to for the structural change in
ing from the spirit of the invention, as will be
the section takes place immediately upon the de
apparent to those skilled in the art, reference
velopment of heat and the increasing of com
will be had to the appended claims for a definition
pressive stresses in the internal layer sufliciently
of the limits of the invention.
What is claimed is:
to force the outer layer to yield. The structure
can thereafter be permitted to cool in air or if
1. An elongated tubular metallic structure of
the character subject in use throughout portions
desired, for rapidity, it may be cooled by place
of its length t0 predominating axial compressive
ment in a cooling bath, or by quenching it exter
nally or internally.
stresses and throughout other portions of its
The heating of the internal layer to a temper 40 length to predominating axial tension stresses,
ature of, for example, 400 degrees F. may not
having the wall of each of said portions comprised
effect any material change in its hardness and
of integral inner and outer layers of metal, said
yet the treatment described will materially in
crease the internal load strength of the casing
section. In some instances, however, it may be
desirable to carry the temperature created in the
internal layer to a point such as to produce a
certain amount of drawing of the original hard
ness of this layer, in which case the internal layer
may be initially hardened to a much higher de
gree than that iinally desired so that the draw
ing action will produce an amount of reduction
in the hardness of the internal layer such as will
inner layers having a yield strength materially
greater than that of the outer layers, said inner
and outer layers of said ñrst-mentioned portions
which are subject to predominating axial com
pressive stresses being under residual compres
sion and tension stresses, respectively, and said
inner and outer layers of said other portions
which are subject to the predominating axial
tension stresses being under residual tension and
compression stresses, respectively.
2. A multi-section oil well casing structure of
produce the hardness desired.
the character wherein incident to weight and ex
While a temperature of 400 degrees Fahrenheit 55 ternal hydrostatic pressure the lower sections
has been suggested, the internal layer obviously
thereof are subject to circumferential collapsing
may be heated to any temperature below the crit
stresses and other compressive stresses and inci
ical hardening temperature, the temperature
dent to the weight of the structure other sec
chosen of course being that which is necessary to
tions thereoí _are subject to axial tension stresses,
produce the desired or necessary upset in the 60 the wall of each section being comprised cf inner
outer layer.
and outer annular layers of metal substantially
The casing sections, as is well known, are
coextensive with the length thereof, said inner
threaded at their ends, as at 20, for attachment
layer being of materially greater hardness than
to adjacent sections through suitable couplings
the outer layer, each of said lower sections having
its inner layer initially under residual compres
It will thus be seen that I have provided an
sion stress and its outer layer initially under re
improved casing string for use in oil wells, or
sidual tension stress, and each of said other sec
under conditions wherein similar conditions exist,
tions having its inner layer initially under resid
by the use of casing sections in which the upper
ual tension stress and its outer layer initially un
portion of the string, wherein tensile strength is 70 der residual compression stress.
of greater importance, have increased tensile
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