, Description:A METHOD FOR WELDING CIRCUMFERENTIAL SEAM WELDING (CIR-SEAMS) OF TWO SUB-ASSEMBLIES OF STEAM GENERATOR
FIELD OF INVENTION
[001] The present invention in general relates to a method of welding of circumferential seam joints in building up shell courses for Steam Generators. In particular, the invention relates to a method of welding of shell with shell butt joints by circumferential seam welding. This invention further relates to a method of welding of circumferential seam by suitably changing the welding process for steam generator sub-assemblies.

BACKGROUND OF THE INVENTION
[002] For manufacturing of circumferential seam joints in building up shell courses for Steam Generators, circumferential seam joints are required. And for long shell courses fabrication, multiple sub-assemblies (shells) are to be integrated by means of Circumferential seam welding (Cir-seams). After a sub-assembly is fabricated it is integrated with its next sub assembly (shell). For joining or integrating any two sub-assemblies (or shells) at first, welding at outer side of shell is furnished which is followed by welding of inside side of the sub-assemblies.
[003] The above said welding involved both SMAW (Shielded Metal Arc Welding) and SAW (Submerged Arc Welding) processes as per Welding Procedure. The original welding sequence of Circumferential seam joints starts with SMAW in the root and hot pass and then followed by SAW welding on the groove till its completion. After completion of the first side (outside) weld, the other side (inside) is to be back gouged and ground to make a groove for defect free welding. This is done to remove the probable lack of fusions in the root- the most probable area for slag entrapment. After the completion of back groove, then new weld layer by SMAW is filled on the back side groove. All these welding are done with 1500C preheat and inter-pass temperature of 2000C. Four hours soaking is required for weld joints for completion of welding. During gouging, 1500C temperature is to be maintained though out the process.
[004] In a conventional process manual gouging and grinding at shell inner side were being done for a length of about 11m. Gouging always produces an uneven / rough surface which is very difficult to grind manually. Groove shoulders and depth becomes uneven throughout the circumference due to these manual operations. Further, the manual process do not provide a smooth and defect free welding.
[005] Manual welding (SMAW) at inside with 1500C preheat creates problems. AN additional protective and monitoring equipment are required when welding is carried out in a confined space. Performing SMAW at shell inside needs a lot of preparation as due to the isolation, difficulty of access and hot work operations (upto 2000C inter-pass temperature) in confined spaces posed additional hazards. Confined spaces normally have little natural ventilation. Weld smoke accumulation, poor illumination, etc. are inevitable. All these resulted in delay in welding and also led to more weld repairs and causes discomfort to workers or performers of welding.
[006] Therefore, and as per the above discussion there is a need for alternate method to establish a change in welding process to improve productivity and to avoid repairs of weld which would result in cost saving.

OBJECTIVE
[007] A main objective of the present invention is to provide for a welding process for Cir-seam welding for sub-assembliess of steam generator.
[008] Another objective of the present invention is to provide for a welding process for Cir-seam welding that results in defect free and smooth welding of the inner side of sub-assemblies of steam generator.
[009] Yet another objective of the present invention is to provide for a welding process for Cir-seams that reduces cycle time and improves weld quality.
[0010] Still another object of the present invention is to provide for a welding process for Cir-seams that eliminates discomfort of the workers or performers performing welding.

SUMMARY OF THE INVENTION:
[0011] To overcome the issues faced in conventional circumferential weld joints, process modification from Shielded Metal Arc Weld to Submerged Arc Weld (SMAW) at inner side of a shell is proposed in the present invention. A smooth groove with uniform profile throughout the circumference is required for welding inner side of sub-assemblies. In the present invention, this is achieved by means of Submerged Arc Weld (SAW) method of welding.
[0012] The present invention relates to a method that avoids back gouging and introduces a grinding process which can create back groove with high speed. The present invention provides for a smooth and defect free weld of inside part of the sub-assemblies.
[0013] In an aspect, the method for circumferential seam welding (Cir-seams) of two sub-assemblies of steam generator, the method comprises of steps of welding of outer side of Cir-seams of the sub-assemblies defining V-groove between the two sub-assemblies which is followed by grinding of the inner side of the welded Cir-seam between the two sub-assemblies to form a semi-circular groove. The grinding is performed by a grinding wheel that is installed on a column and boom arrangement to achieve uniform semi-circular groove. At the end, the welding is performed along the inner semi-circular groove of the Cir-seam by means of a welding machine installed on a column and boom arrangement to achieve uniform welding throughout the Cir-seams of the sub-assemblies.
[0014] In an aspect, in the method of circumferential seam welding (Cir-seams) of two sub-assemblies, the welding is selected from Shielded Metal Arc Welding (SMAW) or Submerged Arc Welding (SAW).
[0015] In an aspect, the method of circumferential seam welding (Cir-seams) of two sub-assemblies the welding is performed by means of a welding machine installed on column and boom arrangement.
[0016] In an aspect, the diameter of the grinding wheel is in range of 500mm to 700 mm and the thickness is in range of 10-30 mm.
[0017] In an aspect, the grinding machine is rotated at speed in the range of 2000rpm to 3000rpm.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0018] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0019] Fig. 1 schematically illustrates side view of the circumferential weld joint in sub assembly.
[0020] Fig. 2 is a schematic cross sectional view of Circumferential weld joint in sub assembly.
[0021] Fig. 3. is schematic cross sectional view of circumferential weld joint with welding sequence.
[0022] Fig.4 is a schematic cross sectional view of grinding of inner side of sub-assemblies by a grinding machine.
[0023] Fig. 5 is a schematic cross sectional view of welding of inner side of sub-assemblies by a welding machine.
[0024] The drawings are illustrative only but not used to limit scope of the present subject matter.

DETAILED DESCRIPTION OF THE CURRENT INVESTIGATION
[0025] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
[0026] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments and detailed in the following description. Descriptions of well-known components and processing techniques are omitted to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0027] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
[0028] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0029] In conventional method, circumferential welding of shells of a steam generator is done with manual back gouging and manual back groove welding. The entire manual operations like manual back gouging, manual back grinding and manual inside groove welding creates more fatigue to task performing groups and reduces efficiency of production. To do segment wise back gouging, grinding, welding and post weld soaking, it requires more man power for completion and this increases the cycle time of seam welding. More chances for weld defect us also there at shell inside due to manual operations. Hence it is required to introduce a method for welding automation to avoid all these drawbacks.
[0030] The present subject matter herein relates to a method of welding of Cir-seams of two sub-assemblies of a steam generator that provides defect free and smooth welding of inner side of the sub-assemblies.
[0031] In the method disclosed in the present invention, each sub-assemblies (shells) 101a and 101b of a steam generator first go through operations like marking, buttering welding, attachment welding, nozzle welding, grinding, NDE, machining, etc. The operations before performing the welding process are known to a person skilled in the art, therefore, the description avoid explanation of pre-welding operations in detail to avoid ambiguity in the subject matter of the invention.
[0032] After the completion of each operation at every sub-assembly go for integration with next sub assembly/ies (shell). Circumferential welding starts after completion of proper fit-up of two sub-assemblies (shells). During fit-up, the mismatch of both the shells 101a and 101b is controlled by adjustable spiders. The inside and outside plane of both shells are kept in the same plane after ovality correction. A groove is formed at the intersection point of the two sub-assemblies by known means such as grinding or cutting. Further, shape and configuration of the groove is similar for all the Cir-seam joints that is defined as single ‘V’ groove 201 (as shown in Fig. 2) joints without any backing ring. Thickness of ‘V’ groove joints varies from 57.5mm and 71.5mm with groove angle of 100±1.
[0033] Fig. 1 illustrates side view of circumferential weld joint defining a ‘V’ groove at the intersection of the two sub-assemblies 101a and 101b.
[0034] Referring to Fig.2, a cross-sectional view of ‘V’ groove 201 is illustrated that is defined at the intersecting point of the two sub-assemblies 101a and 101b.
[0035] Fig. 3 illustrates welding of two sub-assemblies of steam generator which defines a V groove. As indicated by arrow 301, the two sub-assemblies are welded along the V groove using manual welding process which welds outside surface of sub-assemblies. As indicated by arrow 302, inner surface of the welded two sub-assemblies is back grounding and as indicated by arrow 303, the inner surface of two sub-assemblies is welded to achieve smooth and defect free joint.

Claims:We claim:
1. A method for circumferential seam welding (Cir-seams) of two sub-assemblies (101a and 101b) of steam generator, the method comprising:
welding (301) of outer side of Cir-seams of the two sub-assemblies (101a, 101b) defining V-groove;
grinding (302) of inner side of the welded Cir-seam of the two sub-assemblies (101a, 101b) to form a semi-circular groove; and
welding (303) of the inner semi-circular groove of the Cir-seam of the two sub-assemblies (101a, 101b), wherein the grinding (302) is performed by a grinding machine (401) installed on a column and boom arrangement (400).
2. The method as claimed in claim 1, wherein the welding process (301) is selected from Shielded Metal Arc Welding (SMAW) and Submerged Arc Welding (SAW).
3. The method as claimed in claim 1, wherein the welding (303) is performed by a welding machine (501) installed on a column and boom arrangement (500).
4. The method as claimed in claim 1, wherein the grinding machine (401) is installed on a column and boom arrangement (400).
5. The method as claimed in claim 1, wherein the grinding machine (401) has a grinding wheel (402), the grinding wheel (402) defines diameter in range of 500mm to 700 mm and thickness in range of 10-30 mm.
6. The method as claimed in claim 4, wherein the grinding wheel (402) rotates at speed in range of 2000rpm to 3000rpm.