Claims:WE CLAIM:
1. A method of manufacturing of T23 gang bend panel for high pressure and high temperature steam generators comprising steps of:-

- forming of straight panel by securing a plurality of tubes with multitude of fin flats,
- fixing a bend tube with a support lug to form a sub assembly,
- connecting said multiple sub assemblies with said straight panel to obtain assembly,
- placement of a bend plate in between the bend tubes to form the gang bend panel.

2. A method of manufacturing of T23 gang bend panel for high pressure and high temperature steam generators as claimed in claim 1, wherein said securing, fixing, connecting and placement may constitute welding.

3. A method of manufacturing of T23 gang bend panel for high pressure and high temperature steam generators as claimed in claim 1 or 2, wherein the straight panel, length of which is maintained for joining the bend tube in such a way that it is placed at a distance of approximately 300mm from the buck stay attachment.

4. A method of manufacturing of T23 gang bend panel for high pressure and high temperature steam generators as claimed in any of the preceding claims, wherein the bend tube undergoes post bend heat treatment of normalizing and tempering as per table 1 prior to welding of the support lug.

5. A method of manufacturing of T23 gang bend panel for high pressure and high temperature steam generators as claimed in any of the preceding claims wherein the joint between the straight portion of tube and bend tube and the joint between the support lug and bend tube are locally stress relieved.
, Description:A method of manufacturing of T23 gang bend panel for high pressure and high temperature steam generators
FIELD OF INVENTION
[001] The present invention in general relates to method of manufacturing of T23 Gang Bend Panel for high pressure and high temperature steam generators. More particularly the present invention relates to method of Post Bend heat treatment of Normalising and Tempering for bend portion of T23 Back pass Extended Side Fin Welded Panels without requiring whole panel to undergo Normalising and tempering.

BACKGROUND OF INVENTION

[002] In high pressure and high temperature steam generators, panels are pressure part of boiler that forms the enclosure wall of steam generator. Panels mainly consist of tubes, Fin flat and attachments. Water flows through the tubes of panels and get converted into steam by absorbing heat generated in furnace. Material of tubes depends on required steam parameters. T23 material is used for high pressure and high temperature parameters, which is basically low alloy steel with 2.25 Cr-1.6W-V-Nb material .Creep strength of T23 is higher than that of T12 or T22 material. The process of Heat Treatment of T23 material is very stringent and requires very high attention. Panels are formed with tubes and fin flat in panel forming machine. Following Panel Formation, Marking on panel is carried out for Gang Bending of Panels as per Drawing. While marking Bend stretch is taken in account. Panels are bent in Gang bending machine to a specific bending radius as per drawings. A bending Roller mounted on a bending machine is employed for bending the Panels, which is unique for a specific bending radius.

[003] Gang bending is a cold working process and Heat treatment process depends on R/D ratio. The R/D ratio of a bend is the ratio of radius (R) of the bend to mean diameter (D) of a tube. As per the Table 1, the SA213T23 material is subjected to heat treatment process based on the R/D ratio. For the bends with the R/D ratio less than 2.5, the Normalising is done at temperature of 1040-1050 °C and Tempering is done at 750 – 760 °C. Incase the R/D ratio exceeds 2.5 but less than 10 and cold strain portion of panel is likely to be exposed to temperature above 720 °C during fabrication whether purposefully or incidentally or if a weld is to be made on the cold strained portion, then cold strained part is Normalised at 1040-1050 °C & Tempered at 750 – 760 °C. However, no heat treatment is required, when the R/D ratio is more than 10.

Table 1: Post Bending Heat Treatment requirement of T23 (2.25 Cr-1.6W-V-Nb) tubes

MATERIAL COLD BENDING
SA213T23 (A) R/D<2.5,
Normalising at 1040-1050 °C
Tempering at 750-760 °C

(B) R/D=2 & <10 & if cold strained portion is likely to exposed to temperature above 720 °C .
Normalising at 1040-1050 °C
Temper at 745 ± 15 °C

(C) R/D=10, No HT.

[004] The Process of Normalising and Tempering of T23 bends involves high furnace operation cost and higher cycle time. Apart from this, Furnace size is also a big constrain for Normalising and Tempering process for T23 panels owing to its bigger size. Referring to Figure 1, First, straight panel is formed with multitude of tubes (01) and fin flats (02) as per specified Pitches. The tubes of panel shown are having 57.2mm outside diameter with thickness of 7.6 mm, made of T23 material and the radius of bend used is 251mm,

wherein the R/D ratio for this case is 4.39. After Panel formation Panel is bent in Gang Bending Machine and following gang bending of panels, Support lugs (03) are required to be welded to each gang bent tubes. As welding of support lugs to bent tubes definitely exposes the bent tubes beyond temperature of 720 °C, hence as per Table 1, for bent tubes of panel, the Normalising and Tempering are required to be conducted. This Normalising and Tempering need to be done in an encompassed condition i.e. the entire component to be normalised and tempered should be kept inside the furnace.

[005] However, due to high operational cost and size constrains of furnace, it is not possible to incorporate the whole Panel in furnace for Normalising and Tempering of bent portion of panel.

[006] Hence it is imperative to devise a method for Normalising and Tempering of bend portion of Panel without requiring whole panel to undergo the process. The same has been proposed by the present invention, which will be discussed hereinbelow.

OBJECTS OF THE INVENTION

[007] An object of the present invention is to provide a method of manufacturing of T23 gang bend panel for high pressure and high temperature steam generators.

[008] Another object of the present invention is to provide a method of manufacturing of T23 gang bend panel for high pressure and high temperature steam generators which avoids whole panel to undergo normalizing and tempering.

SUMMARY OF THE INVENTION
[009] According to this invention, there is provided a method of manufacturing of T23 gang bend panel for high pressure and high temperature steam generators comprising steps of:- forming of straight panel by securing a plurality of tubes with multitude of fin flats, - fixing a bend tube with a support lug to form a sub assembly, - Connecting said multiple sub assemblies with said straight panel to obtain assembly, - Placement of a bend plate in between the bend tubes to form the gang bend panel.

[0010] Said securing, fixing, connecting and placement may constitute welding.

[0011] The straight panel, length of which is maintained for joining the bend tube in such a way that it is placed at a distance of approximately 300mm from the buck stay attachment.

[0012] The bend tube undergoes post bend heat treatment of normalizing and tempering as per table 1 prior to welding of the support lug.

[0013] The joint between the straight portion of tube and bend tube and the joint between the support lug and bend tube are locally stress relieved.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0014] Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings of the exemplary embodiments and wherein:
Fig. 1 shows: Conventional gang bend panel with welded support lugs.
Fig. 2 shows: Straight portion of panel of the present invention.
Fig. 3 shows: Bent tube with the support lug according to the invention.
Fig. 4 shows: Final panel assembled with bent tubes and support lug in accordance with the invention.

DETAIL DESCRIPTION OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
[0015] The present invention makes a disclosure regarding a method of manufacturing of T23 gang bend panel for high pressure and high temperature steam generators. The process of Normalising and Tempering of bend portion of T23 Gang bend Panel is conducted by doing away with the whole panel to undergo the process. The process of instant invention is completed by dividing the panel into two parts forming one straight portion and other bend portion as illustrated in the figure 2 and 3 respectively.

[0016] The division of Panels into two parts is done in such a way that the joint which is required later should not fall with any attachments coming on panel and should be at least 300 mm away from centre line of Buckstay arrangement.

[0017] Now, reference may be made to Figure-02 wherein the straight portion of panel is formed with a plurality of tubes (01) and fin flats (02) in panel forming machine by welding in which a flat is positioned between two tubes.

[0018] Referring to figure 3, the bend portion includes an individual bend tube (04) and a support lug (03). The bend tube undergoes post bend treatment of normalizing and tempering as per the following table owing to bending operation of T23 grade material. Thereafter, the support lug (03) is welded with the bend tube (04) constituting a sub assembly.

MATERIAL COLD BENDING
SA213T23 (A) R/D<2.5,
Normalising at 1040-1050 °C
Tempering at 750-760 °C

(B) R/D=2 & <10 & if cold strained portion is likely to exposed to temperature above 720 °C .
Normalising at 1040-1050 °C
Temper at 745 ± 15 °C

(C) R/D=10, No HT.

[0019] To form a gang bend panel of the present invention, 10 to 12 such sub assemblies are required, wherein ten gang bend panels are provided per boiler.

[0020] The straight panel as shown in figure 2 is connected with the subassembly of support lug and bend tube preferably by means of Tungsten inert gas (TIG) welding without restricting scope of the invention to the same. Thus, multiple sub assemblies are welded with the straight panel to form the assembly as shown in figure 4 by welding one end of the bend tube and the other end of the bend is welded to header at site.
[0021] The aforesaid method of welding has been given as an example. Thus, other methods readily apparent to a person skilled in the art are understood to be within purview of invention.

[0022] In order to form gang bend panel as best seen in figure 4, the joint between the straight portion of tube (01) and bend tube (04) and the joint between the support lug (03) and bend tube (04) are locally stress relieved. Hence, there is no necessity for the whole panel to undergo stress reliving. Further, a bend plate (05) is fixedly secured in between the bend tubes (04) so as to fill the gap in the bend portion, in which the bend plate can be welded in between said bend tubes (04).

[0023] Each end of the Bend tube sub assembly joining to the straight potion of the panels is selected in such a way that it should be approximately 300mm away from the buck stay attachment (not shown) i.e. the length of said straight panel is maintained for joining the bend tube (04) in such away that it should be located at a distance of approximately 300mm from the buck stay attachment. Said buck stay attachment comprising of a beam held by multitude of stays to the exterior of a masonry wall, as that of a furnace or boiler to keep the adjacent areas of the wall from being forced outward.

[0024] It is to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this invention are intended to be within the scope of the present invention, which is further set forth under the following claims:-