Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
C790150
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Description
Improved Method of Forming a Socket_Weld
Technical Field
The invention relates to a method of forming a socket weld
connection between a tubular element such as a pipe, a nipple or a
nozzle and a second element such as another pipe, a drum, a header
or a tube sheet.
When welding a tubular element such as a pipe, nipple or
nozzle to a second element such as another tube, a boiler drum or a
header or a tube sheet of a heat exchanger, a socket weld is often
used where~n the end of the tubular element is inserted into a recess,
termed a socket, in the surface of the second element. To properly
align the tubular element prior to weld;ng, it is desirable to bring
the end of the tubular element in contact with the seat of the socket.
However, a structure of this type is considerably stressed when the
weld is made and tens;onsare produced in the weld seam which may cause
cracking of the seam when the weld contracts as it cools. For this
reason, contact of the end of the pipe with socket set ;s usually
avolded by back~ng-off the tubular element away from the socket set
such that a gap of approximately one and one-half millimeters is
maintained between the end of the tubular element and the socket seat.
By doing this, the end of the tubular element is free to move axially
downward as the weld contracts thereby relieving stresses in the weld
seam which could otherwise cause cracking of the seam. Unfortunately,
backing the tubular element away from the socket seat is a cumbersome
operation which can also result in inaccurate positioning of the
tubular element.
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Backqround Art
The prior art, U.S. Patent No. 3,003,601, provided for a
socket weld connection between a tubular element and a second element
wherein a portion of the end of the tubular element was maintained
in contact with the seat of a flat bottom socket in the surface of
the second element during the welding process without causing crack-
ing of the resultant weld seam. According to this prior art, the end
face of the tubular element must be machined to provide a relatively
thin rim extending from the end of the tubular element. The tubular
element is inserted into the socket such that the relatively thin rim
extending from the end of the tubular element contacts the flat seat
of the socket, a gap thereby being established between the end of the
tubular element and the socket seat into which the relatively thin
rim is free to deform upon shrinking of the weld.
Disclosure of Invention
According to the present invention there is provided an
improved method of forming a socket weld connection between a tubular
element and a vessel, of the type wherein a recess having a diameter
slight~y greater than the diameter of the tubular element is bored
into the surface of the vessel, the tubular element is inserted into
the recess so as to contact the seat thereof and welding heat is
applied externally around the circumference of the tubular element
at the intersection of the tubular element with the surface of the
vessel. The improvement compr;ses tapering the seat of the recess
from its outer circumference inward at a downward angle with respect
to the horizontal of at least 10 and not more than 15.
The improved method of the present invention possesses the
advantage that the end face of the tubular element need not be
machined to produce a relatively thin rim extending therefrom. Thus
a very time consuming step is eliminated in favor of the simple
operation of tapering the socket seat as the socket is bored into the
second element.
Another advantage of the present invention is that the flat
end face of the tubular element is permitted to contact the seat of
the recess thereby ensuring accurate positioning of the tubular
element within the recess, while at the same time providing a gap
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between the end face of the tubular element and the seat of the recess
so that the tubular element may deform upon shrinking of the structure
after the weld has been made without causing excessive stresses and
cracking within the weld connection. Contact between the end face of
the tubular element and the seat of the socket is limited to a line
contact along the outer circumference of the end of the tubular ele-
ment. This limited contact has been shown to be sufficient to ensure
accurate positioning of the tube, but not great enough to offer
sufficient resistance to deformation to induce excessive stresses
within the weld seam as the weld shr;nks upon cooling.
Brief Description of the Drawing
These and further features and advanta~es of the invention
become evident in the description of the following embodiment shown
in the drawing attached wherein:
Figure 1 is a sectional side elevation view of a tube socket
welded to another tube with a fillet weld in accordance with the
method of the present invention; and
Figure 2 is a sectional side elevation view of a tubular
element welded to a vessel with a single-J groove weld in accordance
with the method of the present invention.
Best Mode for Carryin~ Out the Invention
Referring to the drawings, a tubular element 10 is shown
welded to a second element 20, such as another tube as shown in
Figure 1 or a vessel such as a drum or header as shown in Figure 2.
A recess is bored into the surface of the second element, and the end
face 50 of the tubular element 10 is inserted therein. The recess
may comprise a number of known shapes such as the simple annular
socket 30 of Figure 1 or the more elaborate socket 32 of Figure 2
wherein a weld groove, such as a single-J pipe weld groove, is
embodied in the socket itself. It is desirable to insert the tubular
element 10 all the way into the recess 30, 32 until the end face 50
of tubular element 10 is in contact with the seat 40 of the socket so
that proper and accurate positioning of the tubular element can be
assured.
In accordan~e with the invention, the seat 40 of the socket
30, 32 is tapered from its outer circumference inward at a downward
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angle with respect to the horizontal of at least 10. Although any
taper of an angle greater than 10 ensures that sufficient space is
available for the end face of the tubular element to deform without
causing excessive stresses in the weld seam, it is preferred that the
angle of the taper be limited to not more than 15 in order to avoid
removing unnecessary large amounts of metal from the second element
which could locally adversely affect the structural integrity of the
second element.
In forming the weld, welding metal is deposited externally
around the circumference of the tubular element 10 at the intersec-
tion of the tubular element 10 with element 20 to form a weld seam 60
therebetween. As the weld seam 60 cools and contracts, the outer
circumferential portion of the end face 50 of the tubular element 70
is free to deform inward and downward into the gap between the end
face 50 of the tubular element 10 and the tapered seat 40 of the
socket. Because the tubular element 10 is free to deform, stresses
do not develop within the weld seam 60 upon contraction and the weld
seam 60 is not subject to cracking. The gap 45 between the end face
50 of the tubular element 10 and the tapered seat 40 of the socket is
essential for allowing the desired deformation necessary to produce
the socket weld connection of the present invention.
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