Note: Descriptions are shown in the official language in which they were submitted.
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This application is a division of copending application Serial No.
294455~ filed January 6th 1978.
This invention relates to a method for the fabrication of internally
weld-cladded toroidal bodies such as pipe elbows.
As is known, large pipe elbows generally consist of rela~ively
thick ferritic base structures for reasons of strength and economy and are
provided on the inside with austenitic weld-cladding for protection against
corrosion. In order to produce such elbows, flat sheets are generally hot-
pressed in a die to form torus-sector half-shells. These half-shells are
then heat treated and machined at the edges. Next, the half-shells are
cladded internally and subsequently welded together in two longitudinal
seams. The welding operation is usually accomplished from the outside in the
~ollowing manner. ~i~st, the austenitic cladding layers which protrude at
the seam location in the outermost material layer,i.e.~ in the innermost layer
of the half-shells, beyond the base material are welded tight by means of the
TIG (tungsten inert gas) method. Next, the entire thickness of several milli-
meters of the cladding layer is filled by means of an austenitic welding
material (Arosto 347).
In order to prevent carburization of the austenitic layer during a
subsequent welding together of the ferritic base struckures, it has been
necessary to lay down a so-called Kardo seam as an insulating layer. Such a
seam consists of very low carbon material, the composition of which, for
example, reads in percent by weight: C-0.01; Mo-0.05; Si-0.05; Cu-0.0~5;
P-0.01, S-0.08 and the remainder iron ~Fe). This Kardo seam protrudes ~`utward-
ly beyond the cladding lay0r by a few millimeters, for example, three milli-
meters and thus extends substantially into the base structure at the seam
location of the hal~-shells to be welded. This Kardo seam has thereafter
been followed by at least one manual seam of ferritic welding ma~erial.
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Thereafter> the seam location is filled up, preferably by a submerged arc
welding technique.
However, the Kardo seam which protrudes into the ferritic base
material represents a discontinuity in the strength of the pipe elbow and
must be taken into consideration in designing the wall thickness.
Further, in the known processes for joining the half-shells, the
cross section is generally distorted so heavily that the structure must also
be straightened out aterwards. However, during this straightening process,
elongations and stresses are introduced. This can lead, in a subsequent
annealing operation, to structure chan~es wherein detrimental brittle frac-
ture properties can occur due to the formation of a coarse grain.
AccordinglyJ it is an object of the invention to improve the con-
struction of large toroidal bodies.
It is another object of the invention to improve the britt~e Fract-
ure behavior of a large pipe elbow formed of half-shells which are welded
together.
It is another object of the invention to avoid the need for a Kardo
seam in welding two half-shells together to form a toroidal body.
Briefly, the invention provides a method for internally weld-
cladding toroidal bodies such as pipe elbows.
The method comprises the steps of forming a pair of torus-sector
half-shells, machining the edges of each half-shell, subsequently welding
the half-shells together into a toroidal body and straightening and heat
treating the toroidal body. Thereafter, the invention employs the steps of
applying a weld-clad along tangential generatrix lines on the inside of the
toroidal body and subsequently stress-ànnealing the weld-cladded toroidal
body.
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The method thus welds the half-shells pr;or to being weld-cladded.
As a result, the Kardo seam described above can be omitted so that the ~is-
continuities of strength mentioned above no longer occur. In addition, any
coarse grain which may have formed when the welded-together toroidal body is
straightened out can be made a fine grain again in the subsequent stress-
annealing step. This has not been possible with the previously known!f~bri-
cation methods as described abovè since the already clad torus bodies must
not be exposed to a high heat treatment temperature because this would lead
to detrimental carburization of the austenitic cladding layer.
The heat treatment which may be used includes an annealing of the
toroidal body at temperatures of 900C to 950C and a subsequent quenching
in water, oil or air. In addition, the step of stress-annealing may include
heating of the toroidal body to a temperature of about 600C and a subsequent
cooling in air.
For the sake of clarity, the method and apparatus of the afore-
mentioned application No. 294445 are described below, along with the iven-
tion claimed herein.
These and other objects and advantages of t~e invention wil] be-
come more apparent from the following detailed description and accompanying
drawings in which:
FIGURE 1 illustrates an elevational view of an apparatus for use
in prac~ising the invention; and
FIGURE 2 illustrates a view taken on line II-II of FIGURE 1.
Referring to FIGURE 1, ~he apparatus for internally welding a
toroidal body such as a pipe elbow 11 has a pair of pillow blocks 2, 3 in
which a tilting means 4 is rotatably mounted via bearings 1. As shown, this
tilting means 4 has a pair of side plates 5, 5', in which journals 6, 6' are
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mounted and journalled in the bearings 1. In addTtion, the. tilting means
has a yoke 7 which extends between the side plates 5-, 5'. The center of the
yoke 7 is provided with an eye 8 (FIGURF. 2) on an axis parallel to the prin-
cipal direction of the side plates 5, 5'.
In addition, ~he apparatus has a turntable 10 which is rotatably
mounted via a pivot shaft 9 in the eye 8 of the yoke 7. Further, the pivo~
shaft 9 is stepped at the free end and provided with a thread 12 (FIGuRE~?)
which projects beyond the yoke 7. In order to rokate the turntable 10
relative to the yoke 7, a worm gear 1~ is mounted on the reduced end of the
pivot shaft 9 iTI abutment with a shoulder ~not shown) of the shaft 9 and is
secured against rotation by a key (not shown) and against displacement by a
nut 13 threaded onto the thrcad 12. The worm gear 14 whlch is thus rotatable
about the axis of the shaft 9 meshes with a worm 26 of a reduction motor 28
mounted on the yoke 7 in suitable manner. This motor 28 is program-contro-
lled in a manner (not shown), for example, by a computer.
The height of the pillow blocks 2~ 3 and ~he tilting means 4 are
such that the turntable 10, including the super structures secured thereon
and on the side plate 5', as described below, can be turned through an
angle of 360 about the horizontal axis oF the journals 6, 6'. This hori-
zontal axis also passes perpendicularly through the pivot axis of the turn-
~table 10 so that during the tilting of the turntable 10, the axis of the
pi~ot shaft 9 executes one revolution in a vertical plane 22.
As shown in FIGURE 1, the turntable 10, has a central cutout 20
and a plurality (e.g. 10) of radial mounting slots 21 for clamping of a
toroidal body 11 to be weld-cladded thereon.
; As shown, contrary to the journal 6, the journal 6l extends beyond
the bearing of the pillow block 2. This extension carries a worm gear 25
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which is secured to the journal 6'~ for example by means of a key. In order
to rotate the tilting means 4 about the horizontal axis, the worm gear 25
engages a worm 27 of a reduction motor 29. Thls reduction motor 29 is pro-
gram-controlled in a manner simllar to the reduction motor 28.
A curved outrigger 35 is detachably secured to the tilting means
4 about a center of curvature located on the pivot axis of the pivot shaft
~. In addition, a means is provided for ad~usting the outrigger 35 relative
to the pivot axis and to the plane of the turntable 10. This means includes
a plate 30 provided with a slot 31 through which a screw 24 passes into the
side plate 5' to hold the plate 30 on the side plate 5' and a slotted arm
34 of the outrigger 35. The slotted arm 34 is fastened on the plate 30 by
means of a screw 32 which threads into a region of the plate 30 outside of
the slot 31. In addition, a spacer 33 is provided between the plate 30 and
the arm 34. As shown, the outrigger 35 is curved over most oE its length
and has a radius of curvature corresponding to the radius of curvature of
the toroidal body 11. For bodies 11 of different radii of curvature,
differently curved outriggers 35 are provided. Accordingly, the mounting
of the outriggers 35 to the tilting means 4 is made detachably to permit
ready replacement.
A weld-cladding means 37 is detachably mounted on the outrigger
35 for rotation in a vertical plane relative to the outrigger 35. As
shown, the weld-cladding means 37 is disposed at the free end of the ou~-
rigger 35 so as to be disposed in common with the pivot axis of the turn-
table 10 in the vertical plane 22. The mounting is such that the weld-
cladding means 37 is rotatable relative to the turntable 10 and the tilting
means 4. The weld-cladding means 37 receives welding material in ribbon
form from a roll 40 which is rotatably mounted on the outrigger 35.
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~lternatively, in order to guide the ribbon in a simpler manner, the roll 40
may be disposed on an axis parallel to the pivot shaft 9 rather than in per-
pendicular relation as shown so that the surface of the ribbon is perpen-
dicular to the turntable 10.
The spacer 33 between the plate 30 and arm 34 may consist of an
elctrically non-conductive material and the screw 32 can be surrounded by or
underlayed with an insulator so as to provide a means for electrically in-
sulating the outrigger 35 from the tilting means 4 and the turntable 10.
In this case, welding current can be fed via the o~ltrigger 35 to the weld-
cladding means 37. This can be accomplished in any suitable manner and isnot further described.
The weld-cladding means 37 can be controlled in synchroTIism with
the reduction motor 29 in such a manner that the principal axis o~ the weld-
cladding means 37 always remains vertical in space. ~lowever, it is also
possible to reset the vertical ~osition of the cladding means 37 in the
vertical plane 22 prior to each operation thereof. This is always p~eceded
by an incremental movement or step of the turntable 10 in the tilting
direction.
As shown in ~IGURE 1, the toroldal body forms a 90 angle and is
clamped to the turntable 10 by means of three clamps ~2 in such a manner
that the axis of curvature of the body 11 is coaxial with the pivot shaft 9.
By shifting the plate 30 and the arm 34 in the ranges permitted by the slots,
the outrigger 35 can be set so that the pivot point of the weld-cladding
means 37 coincides with the longitudinal axis, i.e., the center of the cir-
cle generating the toroidal surface of the shaped body 11. Thus~ when the
table 10 rotates, the pivot point of the weld-cladding means 37 is always
located on the core axis 23 of the body 11 as the body 11 rotates about the
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axis of the pivot shaft 9.
In order to fabricate a toroidal body such as a pipe elbow 11, the
following steps are carried out. First, two torus-sector half-shells are
fabricated ~rom suitably cut sheets in a known manner by die forging. These
half-shells are then machined at the longitudinal edges, i.e., prepared for
a subsequent welding operation, for instance, by deburring and cleaning the
edges so as to provide the edges with a surface suitable for welding. The
surfaces are then welded together to form a toroidal body of the two half-
shells. In order to remove any deformation that may have occurred during
welding, the toroidal body 11 is then straightened out and subsequently heat
treated for tempering or removal o stresses due to the straightening opera-
tion, This heat treatment co~sists of amlealing of the toroidal body at
temperatures of 900C to 950C and a subsequent quenching in water, oil or
air.
Thereafter, the toroidal body is aligned on the turntc~le 10 with
the axis of the curvature of the body 11 parallel to the axis of the pivot 9.
The body 11 is then fastened by means of the clamps 42. Unless the outrigger
35 and the weld-cladding means 37 are already mounted and set up with the
welding means 37 in the vertical plane 22, as would be the case in the fabri-
Z0 cation of a number of elbows with the same shapes and dimensions, the out-
rigger 35 is selected according to the curvature of the toroidal body 11 and
is mounted and adjusted on the side plate 5' by means of the plates 30, 31.
The adjustment is such that the welding means 37 is located with its center
of rotation in the vertical plane 22, and more specifically, in the center
of the circle generating the toroida] body 11. During this adjustment, the
welding means 37 canad~antageously be removed from the outrigger 35 i~ the
center of rotation of the welding means 37 is marked at the outrigger 35.
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The body 11, outrigger 35, and welding means 37 are then mutually aligned
so that the pivot point of the weld-cladding means 37 is located on the core
axis 23 of the toroidal body 11 when the turntable 10 rotates about the axis
of the shaft 9. llowever, it is also possible to arrange the weld-cladding
means 37 eccentrically of the axis of the shaft g. This requires the pivot
point to be reset after each incremental tilting of the turntable 10 in the
tilting direction.
The cladding layer is then applied in incremental steps. To this
end, the turntable 10 is rotated about the axis of the shaft 9 by an angle
which corresponds at least to the angle defined by the toroidal body 11.
This constitutes a working forward stroke during which material is applied.
The turntable is then rotated in the opposite direction. This constitutes an
idle reverse stroke during which ma~erial is not applied. Between each two
working strokes, the inc]ination of the turntable 10 is changed in the tilt-
ing direction in accordance with the wid~h of the cladding. This is carried
out by an incremental tilting of the table 10 about the axis of the journals
6, 6' via the reduction motor 29 and gears 27, 25. During this time, the
position of the weld-cladding means 37 is automatically changed relative to
the outrigger 35 in the opposite direction or must be readjusted by hand so
that the cladding means 37 retains a vertical position for each working stroke.
If required, a welding powder funnel which is provided at the welding means
37 can be refilled between the two working strokes. Alternatively~ an auto-
matic feed for the powder may be provided.
After applying the weld-clad along the tangential genera~rix lines
on the inside of the toroidal body, the body 11 is stress-annealed. This
step can be accomplished by heating the finished pipe elbow or toroidal body
11 to about 600C and subsequently cooling the elbow in air.
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