Claims:WE CLAIM:
1. A method for forming triple elbows for panels in high pressure steam generators, wherein
Edge preparation of fins (04) of elbows (02) is done;
Said elbows (02) are tack welded with stub tube (03);
Butt joint between said elbows (02) and said stub tubes (03) is fully welded;
Said welded elbow (02) with stub tube (03) is subjected to radiographic test;
Following the successful radiographic test, said single elbows (02) are tack welded into a single assembly (01) with some root gap;
Said assembly (01) is welded by fusion welding process;
Carrying out dye penetrant test to check for defects in the root area; and
Following the same process to weld from the other side.

2. The method as claimed in claim 1 wherein, the method can be used to make welded triple elbows with square butt or edge preparation between said fins (04).

3. The method claimed as in claims 1 or 2, wherein said root gap between welded triple elbows is 2 to 3 mm for welding.

4. The method claimed as in claims1 or 2, wherein the welding process is a fusion welding process especially Shielded / Manual Metal Arc Welding, Gas Metal Arc Welding or MIG / MAG welding.
5. The method claimed as in claims1 or 2, wherein said method is used to make welded triple elbows using any filler wire / welding consumable suitable to the material for welding.

6. The method claimed as in claims1 &2, wherein said method is used to make welded triple elbows with or without preheating and or post heating.

7. The method claimed as in claims 1 or 2, wherein said method is used to make welded triple elbows by selecting suitable welding voltage (16-18 V), current (120 – 125 A) and travel speed about 150 to 200 mm / min.

8. The method claimed as in claims 1 or 2, wherein said method is used to make welded triple elbows through manual, mechanized, semi – automated, robotic and / or automated welding modes.

9. The method claimed as in claims 1 or 2, wherein said method is used to make welded triple elbows with short / medium / long arc depending upon the welding parameters.

10. The method claimed as in claims 1 or 2, wherein said method is used for welding of similar dissimilar weld joints in making welded triple elbows.

11. The method claimed as in claims 1 or 2, wherein said method is used for elbows made of any material, any size and thickness.

, Description:FIELD OF THE INVENTION
[001] The present invention in general relates to forming of triple elbows by welding instead of forging for super critical boilers, heat exchangers, etc. The present invention in particular relates to the method for forming triple elbows for panels in high pressure steam generators by fusion welding processes (Shielded / Manual metal Arc Welding (SMAW / MMAW), Gas Metal Arc Welding (GMAW or MIG / MAG) to form triple elbows as per ASME or equivalent code, etc.
BACKGROUND OF THE INVENTION
[002] Presently, the triple elbows (Figure 01) are fabricated as a forged piece and are used in panels of super critical boilers. The joining of the elbows with abutting panel tubes is found to be difficult because of variation in elevation and gap at construction site due to design. A welder has to lie down and then tom weld the joints which results in lots of fatigue to the welder and affects the quality of the joints. To increase the flexibility and access for site welds, an extension (spool piece) tubes is welded to the elbow during supply. As the triple elbows are available as a single forged piece, automation of elbow welding with extension tubes could not be made successfully.

[003] The main hindrance is the pitch between the elbows which is very close (14 mm) in the triple elbows. Hence, typically, the elbows are joined with the extension tubes by manual Gas Tungsten Arc Welding (GTAW) process at shop floors and subjected to 100% Radiography Test (RT). This assembly is then welded to the panels. Following this, using manual TIG process, the tubes are joined with the triple elbows. The entire process takes a long cycle time and also there are quality related issues necessitating rework, considering the access limitations.

[004] D1, IN288KOL2014A relates to a method of holding Elbows and reducers for conventional welding process. More particularly, the invention relates to a joining of multi plane bend pipes called steam generator package links in supercritical steam generators. The invention further relates to a device for fabrication of steam generator package links of super critical high pressure boilers.

[005] D2, JP5552226B2 discloses device and method for repairing a core spray line elbow weld joint: An elbow clamp assembly structurally supports or replaces a connection between a main pipe and an elbow pipe. The elbow clamp assembly includes an upper clamp body (12) and a lower clamp body (14) securable on opposite sides of the main pipe in facing relation. The upper and lower clamp bodies are connected by a clamp bolt (16) extendable through the main pipe. An elbow boss (17) is securable to the elbow pipe, and a cross bolt (19) is extendable through the elbow pipe and connected between the elbow boss and the clamp bolt.
[006] D3, JP2012067864A discloses a method in which the synthetic resin welding joint has a joint body 4C which is held to a clamp 5 of a welding device A so as to surround it and to be held thereto, and a pipe end 4A which can be engaged with the end 11A of the synthetic resin tube 11. The pipe end 4A is externally surrounded by a heat generation part 7 of the welding device A in order to heat and weld a joint s formed by the engagement of the tube end 11A and the pipe end 4A, and the joint body 4C can be attached to the welding device A while being externally surrounded by the clamp 5. Outer peripheral irregularities 4B engaged with inner peripheral irregularities 5A formed at the internal periphery of the clamp 5 are formed at the joint body 4C, and in a clamped state, an angular position with respect to the clamp 5 of the joint body 4C around the axial core Y of the pipe end 4A is fixed by the engagement of the inner peripheral irregularities 5A and the outer peripheral irregularities 4B.

[007] Therefore to overcome the productivity and quality related issues in welding of triple elbowsassembly with extension stub tubes in Shop, it is proposed to form them as single elbows to the required size and then weld the extensiontubes were welded with the elbows by automated GTAW / GMAW processwhich are very productive and of consistent high quality. After welding, the single elbows can be joinedas a triple elbow, by welding the webs of the fin together to the exact dimensions without any concerns.
[008] The present invention serves the purpose of ensuring flaw less joints in fusion welding of the elbow fins with square butt edge preparation for increased productivity.

[009] The present invention relates to the process development for joining triple elbows with a different innovative method of welding instead of forging method.
OBJECTS OF THE INVENTION
[0010] It is therefore an object of the invention to develop a welding method to form the triple elbows for super critical boilers to meet ASME code or equivalent code requirement.

[0011] A further object of the present invention is to develop welding method for achieving full penetration welds between the fins of the elbows by fusion welding processes (Shielded / Manual metal Arc Welding (SMAW / MMAW), Gas Metal Arc Welding (GMAW or MIG / MAG) to form the triple elbows.
[0012] A further object of the present invention is directed to improve upon the productivity using the new forming process.
SUMMARY OF THE INVENTION
[0013] According to the present invention, a novel method of forming welded triple elbows in lace of forged triple elbows for super critical boilers has been developed to meet the requirements of ASME code or equivalent code. By using the developed procedure, the fins between the elbows could be welded by fusion welding process with or without edge preparation to achieve full penetration.
BRIEF DESCRIPTIONS OF THE ACCOMPANYING DRAWINGS
[0014] The proposed invention will be better understood by the following description with reference to the accompanying drawings:
Figure 01 shows the forged piece of a triple elbow.
Figure 02 shows the triple elbow as an assembly.
Figure 03 shows the macrographs of the welds and shows full fusion joint without any defect / discontinuity to validate the procedure / process developed.
DETAIL DESCRIPTION OF THE INVENTION
[0015] Figure 02 shows the triple elbow as an assembly (01). Parted single elbows (02) are tack welded with stub tube (03) by welding. After welding of said stub tubes and said elbows as single elbows, said single elbows are reassembled to convert them as a triple elbow (01). The joints are welded between fins (04) for making the assembly.
[0016] In according to the present invention, full penetration welds is achieved between said fins (04) of said elbows (02) to form said triple elbow (01) by the following procedure.
• Edge preparation on said fins (04) of said elbows (02) (square butt, single V or single J groove).
• Tack weld said stubs (03) with said single elbows (02).
• Full welding of butt joint between said elbow (02) and said stub (03) by automated / mechanised/ robotic / manual welding processes.
• Subject the weld to RT.
• Following the successful RT, tack weld said single elbows (02) as an assembly to match the dimensions of the elbow) with a root gap of 2 mm (min).
• Preheat the job (if necessary) and weld the assembly by fusion welding process. Typical welding parameters for SMAW process are given in Table 01.
• After welding from one side, back gouge the weld by grinding.
• Carry out dye penetrant test to ensure that no defect is present in the root area.
• Weld from the other side also.
• Clean the Weld.
• Carry out visual inspection.
• Carry out MPI of the joints to ensure full penetration and to ensure integrity of the triple elbow.
• Assemble the elbow with transition panel and process further as one triple elbow.
Typical welding parameters for SMAW process are shown in Table 01.

Table 01
DESCRIPTION VALUE
Process SMAW
Type of current DCEP
Electrode specification E 8018 B2
Size Dia 3.15
Voltage 16 – 18 V
Current 120 – 125 A
Preheat temp 120° C
Arc length Short arc
Root Gap 2 to 3 mm

Table 02

[0017] In the experimental work, the welded samples were subjected to Tensile and bend test and macrograph of the welds. Since the entire test met the requirements of ASME, it is concluded that the developed welding method could be implemented for fin to fin welding for forming triple elbows.

[0018] The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the specification, the reference numerals are merely for convenience, and are not to be in any way limiting, the invention may be practiced otherwise than is specifically described.
[0019] 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.