FIELD OF THE INVENTION
The present invention relates to a method of controlling distortion in a welding
procedure of tension bars to each of two transition panels disposed back to back.
BACKGROUND OF THE INVENTION
Distortion is the perennial problem in any welding structure. The distortion
results in many undesirable phenomenon. It is established that the distortion
cannot be completely eliminated except being minimized. Especially, when
welding is carried out on one side of an object and if the welds are long, the
problem becomes more complex. Once distortion has occurred, it is the common
practice that distortion is corrected either mechanically or thermally. Alternative
method is to apply weld sequence to control distortion so that the correction is
minimum or avoided. In certain cases, weld sequence alone cannot give
desirable results. Hence weld sequence coupled with other techniques are to be
employed to control distortion.
US Patent Document US 7028882 describes a method for depositing an overlay
weld on a boiler tube panel comprising a plurality of tubes with adjacent tubes
joined together and then straightening the bow that occurs due to overlaying.
However, there is no device and process available to control distortion during the
welding following weld sequence and back to back positioning, so that no
correction of distortion becomes necessary after completion of the welding.
US Patent Document US 6861617 describes a method to minimize buckling
distortion caused by welding in thin plate by utilizing transient thermal
tensioning. Multiple heat sources of variable intensity may be utilized. However,
there is no device and process available to control distortion during the welding
following weld sequence and back to back positioning methods. Our invention is
control of distortion in panel structure comprising plurality of tubes and another
member called tension bars welded on it. Here, weld sequence and back to back
clamping techniques are employed. No multiple heat sources are used.
US Patent Document US 7006958 describes the modeling weld process and
determining the distortion produced. However the invention is developing a
model and there is no practical application described in the patent. Our invention
is related to experimental application of weld sequence to weld tension bars in a
back to back positioned transient panel.
US Patent Document US 5550347 relates to reducing welding deformation in the
case, where steel plates to be welded are butted and subjected to tack welding.
Then the tack welding portion is subjected to one side welding for joining the
plates. The invention does not relate to application of weld sequence. Our
invention differs in the sense that welding distortion is controlled in welding
tension bars to plurality of tubes. In this invention two panels are positioned
back to back and tension bars are welded on one side using weld sequence.
US Patent Document US 5014901 relates to a rotatable welding fixture for
supporting elongated structures such as tubes while performing metal welding
operations on the tube. A plurality of elongated structures such as tubes to be
metal clad welded is supportably attached to the outer longitudinal surface of the
fixture. The invention provides a method for metal clad welding the elongated
structures while being rigidly supported by a rotatable welding fixture. Whereas
our invention differs in the sense that it relates to control of distortion by back to
back positioning of transition panel consisting of plurality of tubes and following
a welding sequence by which plurality of tension bars are welded to the said
panel.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method of controlling
distortion in a welding procedure of tension bars to each of two transition panels
disposed back to back, which eliminates the prior art problems.
Another object of the invention is to propose a method of controlling distortion in
a welding procedure of tension bars to each of two transition panels disposed
back to back, in which the back to back transition panels are clamped.
A still another object of the invention is to propose a method of controlling
distortion in a welding procedure of tension bars to each of two transition panels
disposed back to back, in which the back to back transition panel are disposed in
vertical condition.
A further object of the invention is to propose a method of controlling distortion
in a welding procedure of tension bars to each of two transition panels disposed
back to back, in which a welding sequence is adapted during joining the tension
bars.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, two transition panels are positioned
in back to back condition such that the welding areas for welding the tension
bars do not face each other.
According to a second aspect of the invention, a plurality of clamps at various
locations is provided on either side of the panel for holding the back to back
positioned transition panels firmly.
According to a third aspect of the invention, a fabricated fixture is provided to
hold the back to back panel firmly in vertical position.
According to a fourth aspect of the invention, the tension bars are welded to the
back to back positioned transition panels according to a selected weld-sequence
by employing two welders to weld simultaneously on each panel; and removing
the clamps after completion of welding.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The proposed invention will be better understood by the following description
with reference to the accompanying drawings.
Figure 1 shows a longitudinal view of one transition panel with tension bars
on the panel.
Figure 2 shows the view of two transition panels in back to back position
and in clamped condition.
Figure 3 shows the back to back positioned panels in the fixture in vertical
position.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
A transition panel (Figure 1) forms a part of the water wall panel primarily used
in supercritical boilers This panel is a tubular panel (1), and consist of a plurality
of inter-connected tubes. On this panel, tension bars (2) are placed at discrete
locations between two adjacent tubes and on one side. The tension bars are
welded with both the adjacent tubes. A set of tension bars is placed side by side
in one location. Plurality of sets of such tension bars are placed all through the
entire length of the transition panel which is about 10 metres long. Considering
the length of the panel and also the location of the welds that are present on
only one side, the structure is liable to distort heavily on one direction.
This invention provides a method to avoid distortion during welding of tension
bars to the transition panels. The invention provides a method to keep two
transition panels in back to back condition (Figure 2) such a way that the tension
bars are not facing each other. Then the two panels which are in back to back
condition are clamped rigidly using "V" clamps (3), to avoid any movement
during welding. Each tension bar is welded to two adjacent tubes within which it
is placed. The back to back panels are then positioned in a fabricated fixture
such a way that they are held in vertical position (Figure 3). The fixture is
fabricated out of plurality of channels placed adjacently with a gap between
them so as to accommodate the back to back panel in vertical position. In this
position 50% of number of welds connecting the tension bar to the adjacent
tubes of the tension bars on each panel are welded in down hand position. For
this purpose, two welders are employed to weld the two panels simultaneously.
The invention further provides a procedure for welding of the tension bars that
are present back to back. The selection of weld sequence is from the centre
tube of the panel and subsequent welds are carried out on the tubes on either
side of the centre tube alternately. For example, the first weld is carried out on
the tube that lies in the centre in the width of the transition panel. The second
weld is carried out on the adjacent tube above the centre tube. The third weld is
carried out on the adjacent tube below centre tube. The weld sequence is
followed in this manner by selecting the tubes alternatively on either sides of the
centre tube. The direction of welding for all the welds is from centre of the tube
to the end. After completing this 50% welds on each panel in down hand
position, the panel is turned topsy-turvy. In this position, the remaining 50% of
the welds are carried out in down hand position in the same manner as done
earlier. After welding of the tension bars in the back to back positioned panels
the two panels are set free by removing all the "V" clamps.
The proposed invention as narrated herein above should not be read and
construed in a restrictive manner, as some modifications, adaptations and
alterations are possible within the scope and limit of the invention as defined in
the encompassed appended claims.
WE CLAIM:
1. A method of controlling distortion in a welding procedure of tension bars
to each two transition panels disposed back to back, the transition panels
forming a part of the water wall panel of supercritical boilers, and constituting a
tubular panel having a plurality of inter-connected tubes, wherein a plurality sets
of tension bars are rigidly disposed between adjacent tubes, the method
comprising the steps of:
disposing at least two transition panels in back to back position such that
areas to be welded are oppositely-faced;
clamping the back-to-back positioned transition panels by "V" clamps;
locating the clamped panels in a fixing device in a first vertical position;
down-hand welding of 50% of the welds connecting tension bars to the
adjacent tubes on each transition panel simultaneously by separate
welders, wherein the weld-sequence employed constitutes weld-start at
the centre tube of the transition panel and weld-continuation on the tubes
falling both sides of the center tube of the panel in alternate fashion;
positioning the sub-assembly of the transition panels and tension bars in a
vertically-opposed position in relation to said first vertical position;
welding in an identical weld-sequence balance 50% of the welds
connecting tension bars to the adjacent tubes in down-hand position; and
de-clamping the assembly of the back-to-back positioned transition
panels.
2. A method of controlling distortion in a welding procedure of tension bars
to each of two transition panels disposed back-to-back substantially as
herein described and as illustrated in the accompanying drawings.

ABSTRACT

A method of controlling distortion in a welding procedure of tension bars to each
of the two transition panels disposed back to back, the transition panels forming
a part of the water wall panel of supercritical boilers, and constituting a tubular
panel having a plurality of inter-connected tubes, wherein a plurality sets of
tension bars are rigidly disposed between adjacent tubes, the method comprising
the steps of disposing at least two transition panels in back to back position such
that areas to be welded are oppositely-faced; clamping the back-to-back
positioned transition panels by "V" clamps; locating the clamped panels in a
fixing device in a first vertical position; down-hand welding of 50% of the welds
connecting the tension bars to the adjacent tubes on each transition panel
simultaneously by separate welders, wherein the weld-sequence employed
constitutes weld-start at the centre tube of the tension panel and weld-
continuation on the tubes falling both sides of the center tube of the panel in
alternate fashion; positioning the sub-assembly of the transition panels and
tension bars in a vertically-opposed position in relation to said first vertical
position; welding in an identical weld-sequence the balance 50% of the tension
bars in down-hand position; and de-clamping the assembly of the back to back
positioned transition panel.