Claims:WE CLAIM

1. An automatic method of welding in SA12A sub-assembly of Steam Generator comprising the steps of:
- Marking of joints where buttering to be welded and verification by Quality control;
- Surface Examination-Penetrant test;
- Preheating the job to 150 Degree Celsius;
- Setting the auto welding machine in position using column and boom
c) Setting the filler wire on feeder
d) Filling flux in hopper
- Welding by Submerged arc welding(SAW) as per welding procedure plan (WPP) within the marked area layer by layer to reach minimum thickness of 10mm;
- Post heating of completely welded joints to 280 Degree Celsius;
- Grinding of extra portions of weld to bring it to desired shape and size to carry out Non-destructive examination;
- NDE- Magnetic Particle Test and Ultra sonic test;
- If defects available, removal of defective portion by grinding or gouging as per NDE report, repetition of the process from steps 2 to 8;
- Final dimension verification by Quality control.

2. The method as claimed in claim 1, wherein the welding nozzle is kept stationary and job is rotated at a speed of 450-550 mm/min to the length of buttering as required.

3. The method as claimed in claim 1 or 2, wherein Nozzle position is adjusted using a column and boom arrangement, and each bead is welded in circumferential direction (along the length of buttering).

4. The method as claimed in claims 1 - 3, wherein the current is set in the range of 450-550 Ampere.

5. The method as claimed in claims 1 - 4, wherein each joint is welded by four layers to bring to required thickness.
, Description:A METHOD OF WELDING IN SA12A SUB-ASSEMBLY OF STEAM GENERATOR

FIELD OF INVENTION :
[001] The present invention relates to a method of welding in SA12A sub-assembly of Steam Generator. In particular, the invention relates to welding of Ferritic buttering for Lug plates in sub-assembly SA12A. This invention further relates to automation of Ferritic buttering welding for Lug plates by suitably changing the welding method.

BACKGROUND OF INVENTION :
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[003] Lugs are used for supporting steam generator at site. Lugs are welded on the SA12A assembly after the welding of Ferritic buttering over SA12A assembly. Buttering welding is the process of depositing multiple layers of consumable material over the surface of parent material. Ferritic buttering is welded to avoid laminar tearing of pressure boundaries due to the direct load from lugs. There are four lugs on SA12A assembly which is 900 apart from each other. So there are four buttering over which these lugs are welded. Area of one buttering is 240600 mm2 and height is 10 mm. At present, buttering welding for lugs is carried out by manual welding using Shielded Metal Arc Welding (SMAW) process. The same is as follows:
1. Marking of joints where buttering to be welded and verification by Quality control;
2. Surface Examination-Penetrant test;
3. Preheating the job to 150 Degree Celsius;
4. Welding by Shielded metal arc welding(SMAW) with E-9018G electrode as per welding procedure plan (WPP) within the marked area layer by layer to reach minimum thickness of 10mm;
5. Post heating of completely welded joints to 280 Degree Celsius;
6. Grinding of extra portions of weld to bring it to desired shape and size to carry out Non-destructive examination;
7. NDE- Magnetic Particle Test and Ultra sonic test;
8. If defects available, removal of defective portion by grinding or gouging, repetition of the process from steps 2 to 7;
9. Final dimension verification by Quality control.

[004] Current is set in the range of 140-180 A as per the parameters qualified in the welding procedure plan. Around 2400 numbers of E9018-G electrodes are used for welding. It takes about 30 days to complete 4 joints.

[005] Upon examination, it is found that on an average, about 10% by volume of buttering is defective. The process involves lot of repairs which affects the quality of welding joint. As more repairs evolves, the Non-Destructive Examination becomes more fatigue and time consuming, which further affects cycle time. Hence, there is a need to improve the process to improve quality and reduce cycle time. In view of the above, the present invention has been introduced, which addresses shortcomings of the known arts and serves the purpose efficiently.

OBJECTS OF THE INVENTION :
[006] It is therefore object of the present invention to propose automation of buttering welding for centre plate and Side plates of lug in SA12A sub-assembly, which eliminates the drawbacks of the prior art(s).

[007] Another object of the invention is introduction of Submerged Arc Welding (SAW) to accomplish quality welding and uniform beads in buttering for lug of steam generator.

[008] Another object of the present invention is to reduce cycle time and improve quality.

[009] Still another object of the invention is to eliminate defects and also to achieve more productivity.

[0010] Yet another object of the present invention is to provide a method of welding in SA12A sub-assembly of Steam Generator, which is cost effective.

[0011] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY OF THE INVENTION :
[0012] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus/composition and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.

[0013] To overcome the issues faced in the buttering welding for lug, the welding process switched from Shielded Metal Arc Welding (SMAW) to Submerged Arc Welding (SAW).

[0014] Process modification in sub assembly SA12A by welding automation of Ferritic buttering for centre plate and side plats of lug on shell-III is adopted.

[0015] Instead of manual welding with electrodes, SAW wires with same specifications of electrode are used for the auto welding of joints. In SMAW, job was kept stationary and welder manipulated electrode to complete the joint. Whereas in SAW, Job kept rotating at required speed and welding nozzle kept stationary through which wire was feeding. Adjustment of welding nozzle was carried out by column and boom arrangement. By SAW, welding of four joints completed in 16 days. On examination, job got qualified with zero percentage defect. By this implementation, it was possible to eliminate defects and also possible to achieve more productivity. The SAW process gives a very good weld result in all the Non-destructive tests. All the above merits have resulted in getting quality weld joint without any defects with a very minimum cycle time.

[0016] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

[0017] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.

[0018] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS :
[0019] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein:-

[0020] Figure 1 shows: Top view and side view of buttering weld carried out and ground to final dimensions according to the prior art.

[0021] Figure 2 shows: Front view of lugs welded on buttering in accordance with the prior art.

[0022] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS :
[0023] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

[0024] The instant invention pertains to a technology regarding a method of welding in SA12A sub-assembly of Steam Generator.

[0025] Ferritic buttering welds are given to Steam generator to avoid direct welding of attachment to pressure boundaries as that may cause laminar tearing. Now, reference may be made to Figure 1 and 2. Lugs are welded at four locations on shell-III (04) of SA12A assembly. One number of centre plate (02) and two numbers of side plates (03) are available in each orientation. For this, four “I” shaped buttering welds (01) of circumferential length 780 mm and major width 230 mm are welded. Area of one “I” shaped buttering is 240600 mm2 and thickness is 10 mm. Volume of a joint comes as 2.406×106 mm3. Total volume of four joints comes as 9.624×106 mm3. For welding of centre plate (02) and side plates (03) with SA12A sub assembly, E9018-G electrodes are used and welding is carried out by Shielded Metal Arc Welding (SMAW). It took 30 days on an average to complete welding of four joints. It required 5-6 layers of welding to bring to required thickness considering allowance for grinding for Non-Destructive Examination (NDE). Due to huge volume of manual welding, there are many start-stop points in welding which is prone to welding defects. Due to the presence of many indications, NDE became difficult and it took longer time for evaluation. After attending the repair, the job has to undergo NDE again, which further increases cycle time.

[0026] In order to overcome all these drawbacks, the process has been changed by automation of welding. Process changed from Shielded metal arc welding (SMAW) to Submerged Arc Welding (SAW).

Automated Welding Procedure of the invention is as follows:
- Marking of joints where buttering to be welded and verification by Quality control;
- Surface Examination-Penetrant test;
- Preheating the job to 150 Degree Celsius;
- Setting the auto welding machine in position using column and boom
a) Setting the filler wire on feeder
b) Filling flux in hopper
- Welding by Submerged arc welding(SAW) as per welding procedure plan (WPP) within the marked area layer by layer to reach minimum thickness of 10mm;
- Post heating of completely welded joints to 280 Degree Celsius;
- Grinding of extra portions of weld to bring it to desired shape and size to carry out Non-destructive examination;
- NDE- Magnetic Particle Test and Ultra sonic test;
- If defects available, removal of defective portion by grinding or gouging as per NDE report, repetition of the process from steps 2 to 8;
- Final dimension verification by Quality control.

[0027] The welding nozzle is kept stationary and job is rotated at a speed of 450-550 mm/min to the length of buttering as required. Nozzle position is adjusted using a column and boom arrangement. Each bead is welded in circumferential direction (along the length of buttering).

[0028] Thus automation of buttering welding with SAW process has given solution to the prior problems. It has reduced fatigue of task performers and gave defect free joints. It helped in reducing cycle time with improved productivity.

[0029] Compared to earlier process, cycle time reduced by almost 50%. By this process of invention it is possible to achieve many advantages like high metal deposition rates could be achieved, Welding is carried out without sparks, flash or spatter, Very neat appearance and smooth weld shapes, Faster welding speed, Less risk of user error, More consistent weld, etc. Welding automation gives good Productivity, Consistency, Repeatability, Safety, Quality, Efficiency, Reduced use of Consumables, Reduced Production Costs, Reduction in Weld Distortion, Increased Competitive Advantage and finally the total time to market will be drastically reduced.

Working Example
[0030] A single “I” shaped buttering (01) can be divided as five rectangular sections. Four small rectangles of size 230mm × 75mm and one big rectangle of size 780mm × 150mm. Each rectangle is welded along the length one by one to finish one complete “I” shaped buttering (01).

Advantageous Features
[0031] In SAW, the current is set in the range of 450-550 A, compared to low current of 140-180 A in SMAW. This ensures extra penetration of beads which removes trapped defects from previous bead. As SAW uses flux as shielding material, it eliminates huge amount of welding fumes and hence reduces welder fatigue. Each joint has to be welded by only four layers to bring to required thickness.

[0032] By this method, welding of four joints is completed in 16 days. SAW could bring uniformity of weld beads which helped to control the amount of consumable thus reduction in material cost. All the four joints have cleared in NDE with zero percentage defects.

[0033] It saved repair cost, manpower and reduced cycle time. As it is automated welding, the skill required for welders is comparatively less and employee fatigue is also less. The improved quality in welding has improved customer satisfaction also.

[0034] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0035] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

[0036] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances, where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.

[0037] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0039] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.

[0040] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.