FIELD OF THE INVENTION
The present invention relates to a technique and a method of weld sequencing to be adopted in fabrication of BOILER CEILING GIRDER for high pressure boiler applications with a view to control the welding induced distortion. More particularly, the invention relates to a method of controlling distortion during fabrication of ceiling girder by employing an unique welding sequencing technique.
BACKGROUND OF THE INVENTION
Distortion is a perennial problem during fabrication of larger welded structures. Distortion is a shape change phenomena which is associated with dimensional deviations. Distortion is a recurrent problem in such applications. The occurrence of distortion is attributable to the localized heating and cooling effects associated with the weld including the consequential shrinkage forces of the weld material which produces a bending moment to cause distortion. 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 should be minimized to an acceptable level. Once the distortion has occurred, it is a common practice that one has to go for correction of the distortion either mechanically or thermally. This increases 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, different weld sequencing technique, so that it is well controlled within the tolerable limits.
The fabrication of these girder pieces involves huge amount of welding and hence are prone to welding induced distortion.
US Patent Document US 5550347 describes a method of optimizing welding conditions for reducing welding distortion to a minimum by reducing a heavy burden imposed on preparation work for welding and a welding apparatus. According to this prior art, welding for joining plates in which steel plates to be welded are butted against each other, a tack-welded bead is formed and fixed in a groove.
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, welding of

ceiling girder, a structural member employed in supercritical/sub-critical boiler applications with a special weld sequencing method.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method of
controlling distortion during fabrication of ceiling girder by employing an
unique welding sequencing technique.
Another object of the invention is to propose a method, of controlling
distortion during fabrication of ceiling girder by employing an unique
welding sequencing technique, in which the job is uniquely positioned
during welding to avoid distortion.
A further object of the invention is to propose a method, of controlling
distortion during fabrication of ceiling girder by employing an unique
welding sequencing technique, in which weld zones for simultaneous
welding on the grider without distortion are selected and distributed.
SUMMARY OF THE INVENTION
Accordingly, there is provided a method of controlling distortion during fabrication of ceiling girder involving significant amount of welding, both

butt weld as well as fillet weld, by employing a weld sequencing technique.
According to the invention, a distortion control method for controlling the welding induced distortion of ceiling girder of high pressure boilers is disclosed. The girder is fabricated from C-Mn steel. The web of the beam call for longitudinal grooved butt joint.
Present invention addresses the issue of distortion in the girder as well as method of minimizing the residual stresses by specific sequence of welding, particular locations holding and supporting the girder. A unique method is used to arrive at optimum location of the holding or supporting points while carrying out welding on the job. In addition, to carry-out a butt welding between two pieces of web plate, the groove and fillet welds between web and flanges are necessary, which is minimized to control distortion control. Present invention sufficiently covers the distortion effects of web to flange weld joints too.
According to the invention, a method of welding the ceiling girder used in high pressure boiler application including a weld sequencing technique is disclosed. The ceiling girder is a beam of I-cross section comprising a flange and a web welded together by groove and fillet welds. The web

plate grove butt joint is completed first using determined number of welders. The determined number of welders is arrived based on the part weld length calculated from the production drawing. Each welder continuously carry-out a weld of length l/n (considering ‘l’ as total weld length and ‘n’ as number of welders carrying out the weld.) The invention establishes that by deploying optimum number of welders ‘n’ and by following the sequence detailed herein, welding induced distortion is controlled to a desired level.
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 process flow of joining a web plate of the ceiling girder
by butt weld (double-V)
Figure 2 shows joining of the web plate and a girder flange by groove and
fillet weld.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
This invention describes the method of controlling welding induced distortion in welding of ceiling girders of high pressure boilers. Figure 1 & 2 each shows a schematic process of a typical joining of web and flange plate of the ceiling girder used in boiler structural application.

To mitigate the problem of welding induced distortion, a method of weld sequencing has been disclosed in this invention. According to this method, an optimum number of welders perform the welding of the ceiling girder simultaneously. First, the top flange (01) is welded with the long web (02) by means of conventional Shielded Metal Arc Welding (SMAW) process by the method described below:
In the side ‘A’ of the ceiling girder, positioning of each welder along the path of welding is selected so as to minimize the detrimental effects of welding induced distortion. In figure-1, typically the welders are positioned locations at a,b,c, and d and will be carry out weld lengths of q,r,p and s respectively. The welder position, number of welders and length of weld per welder are determined based on the specific requirement of distortion control. Simultaneously, the welders start welding from the center of the girder and complete each of the butt welds between the web plates and proceed towards the left/right end of the girder and complete all the butt welds in this manner. Thereafter, the same process is repeated to weld the long web (02) with a short web (03). In the same sequence, the bottom flange (04) is welded with the short web (03). Thus, the whole butt welding is completed by conventional Shielded Metal Arc Welding (SMAW) process. This procedure can

effectively control the welding induced distortion in ceiling girders used in high temperature and high pressure boiler applications.

WE CLAIM:
1. A method of controlling distortion during welding of ceiling girders of
high pressure boilers comprising the steps of:
- simultaneously welding the girders at four locations (a,b,c,d), wherein the first welding sequence starting from the centre line and moving upwardly and downwardly to locations ‘a’ and ‘b’ respectively, wherein the second welding sequence commencing from an upper half location (2) to vertically moving further to reach at location (c), and wherein the third welding sequence commencing at bottom half portion (3) and downwardly moving further to reach at location ‘d’.
2. The method described as in 1, welding is completed between the flange (01) and the long web (02), between long web (02) and (03) and finally short web (03) and flange (04);
3. The method as claimed in claim 1, wherein the welding sequence is established by the relationship of I/n where I is the length of weld and n is the number of welding points.