FIELD OF THE INVENTION:
The present invention relates to a method of connecting tube ends of variable diameter in the manufacturing of Fin welded Furnace Roof Panels of OTSC Steam generator. More particularly, the present invention relates to manufacturing of furnace roof panel without machined inserts.
BACKGROUND OF THE INVENTION:
The furnace roof panels are manufactured with tubes and fin flat in panel forming machine. Each panel tube consists of two portions, one portion comprising tubes with lower outer diameter (OD) and other portion comprising tubes with higher outer diameter. Requirement needs to connect these two portion of tubes of variable diameter by using machined inserts. Using straight tube butt (STB) welding process (GMAW), the machined inserts are welded with tube at both ends. Thus there are two STB joints on either side of machined inserts and failing on each tube of panel. 11 panels having total 216 nos. tubes are required to manufacture for each steam generator. There will be total 432 STB joints and 216 nos. of machined inserts are required. For manufacturing machined inserts, raw material of higher wall thickness tubes are machined to achieve required OD at each ends. Real Time Radiography test to be conducted on 432 nos. of STB joints.

Fig 1 shows the machined inserts (03) which is conventionally used to connect two tubes of different diameter. These inserts are manufactured by machining higher wall thickness tube.
Fig 2 shows conventional method of the panel tubes consist of the following items. Tube with lower OD (01) Machined inserts (03) and Tube with higher OD (02) which is welded together by Straight tube butt welding. The Insert (03) as shown in fig 1, is to be machined to get different OD at the two ends from high wall thickness.
Hence it is imperative to find a different method of connecting lower diameter tube with higher diameter tube which can eliminate the use of machined inserts and can also reduce the work relating to STB joints.
OBJECT OF THE INVENTION:
1. The main object of the invention is to develop a method to manufacture the furnace roof panel without the use of machined inserts.
2. Another object of the invention is to develop a method to manufacture the furnace roof panel without the use of machined inserts that reduces one state tube butt (STB) joint for each set of panel tube as well as reducing the real time radiography test.

SUMMARY OF THE INVENTION
The present invention relates to method of manufacturing of furnace roof panel
without the use of machine inserts.
According to present invention, diameter at one end of the higher size tube will be reduced to the diameter matching with the lower size tube by swaging of higher diameter tube. The reduced diameter end of higher size tube will be connected with the lower size tube using straight tube butt welding process.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig 1 shows the machined insert.
Fig 2 shows the prior method of connecting tubes with inserts.
Fig 3 shows tool set up for swaging.
Fig 4 shows panel tubes with swaged end of higher OD tube welded to smaller
OD tube.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION:
According to the present invention, there is provided a method to do swaging of the higher OD panel tube to arrive at the required OD at the end of the panel tube itself.

In fig 3, tools set up for swaging is shown. Tool set up consists for mainly the following:
Parts clamping die (04), swaging die (05), Die casing (06) and straightening die (07). The diameter of tube with higher diameter (02) is reduced by forcing it into a confining die. The clamping die holds the tube properly. The swaging die (05) is open wider at one end thereby accommodating larger diameter part of tube. Die casing (06) encloses the Die (05) firmly. The swaging die (05) reciprocates which provides radial compressive impact force to cause the tube metal to flow inward and acquire the form of the die cavity, In order to maintain the straightness and diameter of swaged end a straightening die is used. After swaging stress relieving operation is performed to remove the induced internal stresses and to increase the mechanical properties of the tube. The reduction in diameter results in increase in the tube length. The increased length is cut to maintain the required length of tube.
As shown in Fig 4, diameter of tube with higher diameter (02) suitably reduced to required lower diameter by swaging and welded with tube with smaller OD (01) by straight tube butt welding process (GMAW).

We claim
A method of manufacturing furnace roof panel by connecting a higher diameter tube with lower diameter tube comprising:-
- Gripping one end of the higher diameter tube (02) in clamping die (04).
- Forcing the swaging die (05) through one end of the tube (02).
- Compressing the diameter of the tube (02) to arrive the required diameter.
- Straightening the swaged portion in straightening die (07).
- Stress relieving to remove induced internal stresses.
- Maintaining the required length of the tube (02) by cutting the additional length of tube (02), generated due to reduction in the diameter of the tube (02).
- Performing weld edge preparation at the swaged end of the tube (02).
- Welding the swaged end to the lower diameter tube (01) by straight tube butt welding process (GMAW).
- conducting radiography test on the welding joint.