FIELD OF INVENTION
The present invention relates to a method of weld sequencing to control distortion in welding of burner panels of high pressure, high temperature steam generator of power plant. More particularly, the invention relates to a method of weld sequencing where eight numbers of welders are employed working simultaneously for controlling the distortion during welding of burner panel.
BACKGROUND OF INVENTION
Distortion is a recurrent problem in case of components fabricated by welding. The occurrence of distortion is attributable to the localized heating and cooling effects associated with the weld and the consequential shrinkage forces of the weld material. This shrinkage force acts with respect to the neutral axis of the component and produces a bending moment which in turn causes distortion of the welded component. Distortion in welded components lead to several undesirable effects like loss of aesthetics, problem of matching in case of assembly and reduction of service life etc. Although welding induced distortion cannot be eliminated completely, it can be minimized to an acceptable level by following various distortion control methods which includes special techniques like sequential welding, back to back welding, addition of restraints, presetting

etc. The problem of welding distortion is more prominent in components where the length of weld is high. Once distortion has occurred, it is a common practice that one has to go for correction of distortion either mechanically or thermally. This adds up to the both cycle time and cost of manufacture on account of the additional rework required to correct the distortion. Therefore the ideal solution is to employ case specific methods for mitigation of distortion during the welding of components itself by following methods like weld sequencing so that it is well controlled within the tolerable limits.
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, this patent does not disclose any details regarding the weld sequencing aspects to be followed for fabrication of such tubular panels so that the welding induced distortion is minimized at the time of fabrication itself. But, the present invention discloses a method of controlling distortion during welding of burner panels by employing a weld sequencing technique and therefore different from the US patent US 7028882 mentioned above.
US patent 7703660 B2 refers to a method of determination by numerical modeling and application of an optimum welding sequence that reduces the welding induced distortion and residual stress formation while depositing hard-facing layers on a boiler water wall panel. Our invention is

different in the sense that it is concerned with welding of burner panels employed in high pressure, high temperature steam generator with a special weld sequencing method and is not related to hard-facing operation that is addressed in the US patent 7703660 B2 mentioned above.
US patent US 6023044 discusses a control method in a multi-layer welding where the weld line and a gap width of work pieces to be welded are detected by a laser sensor mounted on a robot, during a welding for a first layer and welding conditions are adjusted in accordance with the detected gap width for a second and subsequent layer and performed by using the stored data in such a manner that the welding torch is made to follow the weld line, and the welding conditions are adjusted in accordance with the gap width. But, in our invention, a method of weld sequencing for the purpose of controlling welding induced distortion in welding of burner panels used for high pressure, high temperature steam generator has been described.
US patent 5591363 describes a process of depositing layers of weld metal onto a ferrous NiMoV low alloy steel turbine component, where during the deposition of a first layer of weld metal, low levels of amperage are used to prevent a dramatic increase in a level of hardness of the HAZ and during the deposition of a second layer of weld metal, higher levels of amperage are used to temper the heat affected zone. But, our invention relates to a method of

sequencing deposition of welds in welding of burner panels used for high pressure, high temperature steam generator.
The present invention discloses a method of weld sequencing to be adopted in welding of burner panel for high pressure, high temperature steam generator. Fossil boilers are used in thermal power plants for the conversion of water to superheated steam which turns the turbine thereby producing electricity. These fossil boilers comprise of tubular panels called as water wall panels which are composed of tubes and fins welded alternately. The burner panel is located in all four corners of these water wall panels. There are provisions made in the burner panel for admittance of fuel into the boiler for its combustion. The fuel enters through all the burner panels located in all the four corners of the water wall panels and is burnt in the boiler to generate heat which is absorbed by the water that flows through the inside if the tubes in the water wall panels. These burner panels are also tubular panels with tubes and fins welded alternately with the tubes bent in multiple planes. These are typically long welded structures which are highly prone to welding induced distortion. The method of weld sequencing that would control the welding induced distortion in such burner panels has been disclosed in this invention.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a method of
weld sequencing to control distortion in welding of burner panels of high

pressure, high temperature steam generator of power plant, which employs eight welders to work simultaneously for controlling welding induced distortion of burner panel.
SUMMARY OF THE INVENTION
According to the invention, a distortion control method for controlling the welding induced distortion of burner panel of high pressure, high temperature steam generator, is disclosed. The burner panel is a tubular panel of alternately welded tubes and fins. The tubes and fins are bent in multiple planes. The total length of the panel will be over 10 metres and the number of tubes will be over 300. There are fillet weids between the tubes and fins. Each tube (except the first and last tubes) is welded to two fins one placed on the right and the other placed on the left. Therefore, each tube (except the first and last tubes) will take four fillet welds; two each to connect to the fins present on the left and right sides. High volume of heat input imparted by welding would lead to distortion of the component.
To mitigate the problem of welding induced distortion, a method of weld sequencing has been disclosed in this invention. According to this method, there will be a total of 8 welders who will perform the welding of the burner panel simultaneously. Out of the eight welders, four each will be available in the front and back side of the burner panels. Out of the four welders available in the

side 'A' of the burner panel, two welders started from the center of the panels completed each of the fillet welds between tubes and fins and proceeded towards the right end of the panel and completed all the fillet welds in this manner. Simultaneously, the remaining two welders started from the center of the panel completed each of the fillet welds between the tubes and fins and proceeded towards the left end of the panel and completed all the fillet welds in this manner. Similarly, the four welders on the other side i.e. side 'B' completed the fillet welds between the tubes and fins by starting from center and proceeding towards both the right and left end of the panel in the same method as had been stated for side 'A' concurrently along with side 'A' welding. Now, the panel is inverted and the bottom side welds are also completed by following the same method followed prior to inverting the panel. This procedure can effectively control the welding induced distortion in burner panels used in high pressure, high temperature steam generator applications.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows the schematic sketch of burner panel
Figure 2 - shows the sectional view of the panel at the section A-A.
Figure 3- shows the schematic sketch of burner panel with representation of position of welders.

Figure 4 - shows the schematic illustration of welding sequence and direction.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
This invention describes the method of controlling welding induced distortion in welding of burner panels of high pressure, high temperature steam generators. Figure 1 shows the schematic sketch of a typical burner panel used in such applications. The cross sectional view of the panel shown in figure 1 taken along the section A-A is shown in figure 2. The burner panel as seen from figure 2 is composed of tubes (1) welded with fins (2) in an alternate manner. There can be any number of tubes and fins in the panel depending upon the design of the panel. It is also seen from figure 1 that the tubes and the adjoining fins in certain areas of the burner panel are bent in multiple planes. The fins between two adjacent tubes are welded to them by means of four fillet welds namely one group of two fillet welds represented as (3) in the top side of the burner panel and one more group of two fillet welds represented as (4) in the bottom side of the burner panel (figure 2). The detailed welding procedure followed is listed in steps as below.
i. Four welders per side (totally eight welders - Wl, W2, W3 and W4 on side A and W5, W6, W7 and W8 on side B) are employed simultaneously

to carry out the tube-to-fin welding in both side A as well as side B on the top side of the panel as shown in the figure 3. ii. In the position shown in figure 3, initially only the vertical welds (7) are carried out first. The horizontal welds (5) and the inclined welds (6) are taken up after completion of vertical welds (7). The welding sequence stated in steps mentioned hereinafter (steps iii to xiii) is followed for completion of the vertical welds (7) first and subsequently for horizontal welds (5) and inclined welds (6). iii. In figure (4), the double dashed line represents the burner panel, the point (C) refers to mid-length of the overall burner panel and the points (L1) and (Rl) are located at a distance of L/4 from (C). The points (L2) and (R2) represent the left and right extremities which are respectively located at a distance of L/4 from points (L1) and (Rl). The V here refers to the total length of the panel as indicated in figures 1 and 4. iv. The first welder (indicated as Wl on the side A in figure 3) commenced welding from the centre (C) and proceeded towards the right side of the panel till the point (Rl) (figure 4) and completed the fillet welds (3) between all the tubes and fins available in the side A, top side of the panel in the span (C) to (Rl) (figure 4). v. The second welder (indicated as W2 on the side A in figure 3) started welding from (Rl) and proceeded towards the right end (R2) of the panel

and completed the fillet welds (3) between all the tubes and fins available in the side A, top side of the panel in the span (Rl) to (R2) (figure 4). vi. The third welder (indicated as W3 on the side A in figure 3) started welding from the centre (C) of the panel and proceeded towards the left side of the panel till the point (L1) (figure 4) and completed the fillet welds (3) between all the tubes and fins available in the side A, top side of the panel in the span (C) to (L1) (figure 4). vii. The fourth welder (indicated as W4 on the side A in figure 3) started welding from (L1) and proceeded towards the left end (L2) of the panel and completed the fillet welds (3) between all the tubes and fins available in the side A, top side of the panel in the span (L1) to (L2) (figure 4). viii.The fifth welder (indicated as W5 on the side B in figure 3) commenced welding from the centre (C) and proceeded towards the right side of the panel till the point (Rl) (figure 4) and completed the fillet welds (3) between all the tubes and fins available in the side B, top side of the panel in the span (C) to (Rl) (figure 4). ix. The sixth welder (indicated as W6 on the side B in figure 3) started welding from (Rl) and proceeded towards the right end (R2) of the panel and completed the fillet welds (3) between all the tubes and fins available in the side B, top side of the panel in the span (Rl) to (R2) (figure 4).

x. The seventh welder (indicated as W7 on the side B in figure 3) started welding from the centre (C) of the panel and proceeded towards the left side of the panel till the point (L1) (figure 4) and completed the fillet welds (3) between all the tubes and fins available in the side B, top side of the panel in the span (C) to (L1) (figure 4). xi. The eighth welder (indicated as W8 on the side B in figure 3) started welding from (L1) and proceeded towards the left end (L2) of the panel and completed the fillet welds (3) between all the tubes and fins available in the side B, top side of the panel in the span (L1) to (L2) (figure 4). xii. It is to be ensured that all the eight welders Wl to W8 carried out welding in accordance with the procedural steps (iv) to (xi) mentioned above simultaneously i.e. all the eight welders start, perform and terminate welding concurrently. xiii.AII the vertical welds (7) in the top side of the burner panel are completed in the 3G welding position using the procedural steps (iv) to (xii) mentioned above. xiv. The burner panel is then inverted upside down i.e. turned by an angle of
180°. xv. After so turning the burner panel, the vertical welds (7) available in the bottom side of the panel (i.e. fillet welds (4) as shown in figure 3) are welded by employing eight welders (Wl to W8) following the same

procedural steps (iv) to (vii) as had been followed for welding the fillet welds (3) available in the top side of the burner panel.
xvi. After completion of vertical welds (7) available in the bottom side of the panel following the procedure mentioned in step (xv) above, the horizontal welds (5) available in the bottom side of the panel are completed by employing eight welders (Wl to W8) following the procedural steps (iv) to (vii).
xvii. After completion of horizontal welds (5) available in the bottom side of the panel following the procedure mentioned in step (xvi) above, the inclined welds (6) available in the bottom side of the panel are completed by employing eight welders (Wl to W8) following the procedural steps (iv) to (vii). With this all the welding in the bottom side of the burner panel are completed.
xviii. The burner panel is then inverted upside down i.e. turned by an angle of 180° for the second time.
xix. After so turning the burner panel for the second time, the horizontal welds (5) available in the top side of the panel (i.e. fillet welds (3) as shown in figure 3) are welded by employing eight welders (Wl to W8) following the procedural steps (iv) to (vii).
xx. After completion of horizontal welds (5) available in the top side of the panel following the procedure mentioned in step (xix) above, the inclined

welds (6) available in the top side of the panel are completed by employing eight welders (Wl to W8) following the procedural steps (iv) to
(vii). xxi. It is to be ensured that the single pass of welding with least possible
heat input is used for deposition of all welding described in the steps (iv)
to (xx). xxii. suitably tilted so as to bring the vertical welds (7) available in the
bottom side of the panel in 1G welding position
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 weld sequencing to control distortion in welding of burner panels of high pressure, high temperature steam generator of Power plant, the said method comprising;
employing a plurality of welders (W1 to W8) to work simultaneously to carry out tube to fin welding in both sides A and B of each of top and bottom side of the panel (P);
completing vertical weldings (7) available in top side of Panel (P) by employing a plurality of welders;
commencing welding by first welder (W1) from Centre (C) and proceeding towards right side of panel (P) till point Rl to complete fillet welds (3) between all the tubes (1) and fins (2) available in side A of top side of Panel
(P);
starting welding from (R) by second welder (W2) proceeding towards R2
to complete fillet welds (3) for all tubes (1) and fins (2) available in side A of
top side of Panel (P) in the span R1 to R2;
initiating welding by third welder W3 from centre (C) to point L1 to
complete fillet welds (3) for all tubes and fins available in side A of top side of
panel (P);

starting welding by fourth welder W4 from point L1 to L2 to complete fillet welds (3) for all tubes (1) and fins (2) available in side A of top side of panel
(P);
commencing welding by fifth welder W5 from centre (C) to point R1 to
complete fillet welds (3) for all tubes (1) and fins (2) available in side B of top
side of panel (P);
starting welding by sixth welder W6 from Rl to R2 to complete fillet we|ds (3) for all tubes (1) and fins (2) available in side B of top side of Panel (P);
commenting welding by seventh welder W7 from the centre (C) to the point L1 to complete fillet welds (3) for all tubes (1) and fins (2) available in side B of top side of Panel (P);
initially welding by eight welder (W8) from point L1 to L2 of the panel (P) to complete fillet welds (3) for all tubes (1) and fins (2) available in side B of top side of Panel (P);
inverting the burner panel (P) upside down by an angle of 180°;
arranging welding vertical welds (7) available in the bottom side of the Panel (P) to complete fillet welds (4) by a plurality of welders;
arranging welding by a plurality of welders the horizontal welds (5) and inclined welds (6), available in the bottom side of panel by employing a plurality of welders;
turning again the burner Panel (P) upside down by an angle of 180°;

arranging welding horizontal welds (5) and inclined welds (6) available in the top side of the Panel (P) to complete fillet welds (3) by employing a plurality of welders;
wherein,
the said welders are employed to start, perform and terminate welding concurrently while carrying out the tubes-to-fins welding in both side A and B of the top and bottom side of the panel to effectively control the welding induced distortion in burner panes used for high pressure, high temperature steam generator.
2. The method as claimed in claim 1, wherein eight numbers of welder are employed simultaneously to carry out the procedural steps of weld sequencing for the purpose of controlling distortion of burner panels (P).