FIELD OF THE INVENTION
The present invention relates to an edge preparation method and welding of a main plate with a support shell of a lifting attachment assembly to lift steam generator components.
BACKGROUND OF THE INVENTION
During fabrication of a lifting attachment assembly for lifting of heavy weight steam generator components, a crack is normally initiated and propagated in the weldment involving a main plate and a support shell of the lift attachment assembly. Therefore, the weldment warrants a Non Destructive testing for example/ Ultrasonic Testing (UT) to avoid crack initiation and propagation during lifting operation. The prior art used an Edge Preparation method which has TIG at the root welding followed by a further layer through a SMAW Welding. This prior art solution involves welding of a main plate having dimension of say L= 2960mm W=3250mm T=40mm with a support shell of diameter and thickness of 2860mm and T=32mm, the fusing of the root being difficult, there arises rework (incomplete penetration in the weldment inside the shell), which required either gouging/grinding inside the shell at a depth of say, 690mm. At this depth it is again quite difficult to do either grinding or gouging, and results in higher cycle time of the product as well as producing weldments with higher percentage of defects.
Figure 1 shows the prior art edge preparation method, involving a groove angle of 40° with tolerance of +5, -0mm and a root gap 0.9 to 1 mm.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an edge preparation method

and welding of a main plate with a support shell of a lifting attachment assembly to lift steam generators.
Another object of the invention to propose an edge preparation method and welding of a main plate with a support shell of a lifting attachment assembly to lift steam generators, which eliminates rework in internal circumference of the support shell.
A further object of the invention is to propose an edge preparation method and welding of a main plate with a support shell of a lifting attachment assembly to lift steam generators, which produces defect-free weldment.
SUMMARY OF THE INVENTION
Accordingly, there is provided an edge preparation method and welding of a main plate with a support shell of a lifting attachment assembly to lift steam generators, comprising the steps of positioning the main plate (1) upto the water level of the generator and mounting the support Shell (2) over the main plate (1), wherein the edge preparation of the support shell (2) by generating an internal groove at 40° groove angle on the outer side of the support shell (2) at a horizontal distance maintaining horizontally the root face at about 25% of the total distance and the remaining horizontal distance of 75% being used for chamfering at an angle of 40°; maintaining a root gap of 1 to 3.5 mm (vertical distance) between the main plate (1) and the support shell (2); initially conducting a first layer of SMW welding inside the shell, followed by back grinding / back gouging from outside circumference of the support shell (2)', conducting a magnetic particle inspecting (MPI) in the root layer from outside the surface shell; conducting a second layer of welding including (MPI); and filling the remaining groove by conventional SMAW process.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows the Edge preparation style of the existing method.
Figure 2 shows the Edge preparation style in the first experiment.
Figure 3 shows the Edge preparation style in the second experiment.
Figure 4 shows the Edge preparation style with optimized design.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Referring to figure 2, the weldment consisting of a main plate (1) is positioned to the water level, then positioned to a support Shell (2), which has undergone Edge Preparation step, is mounted over the main plate (1). First, the weldment as per figure (2) is done, here edge preparation step is same as figure (1) (i.e.) in both types, a root face (R) and groove angle (e) except gap (d) is increased in order to directly commence the SMAW process. However, thus experiment was not satisfactory since it also has created root defects. Secondly, the weldment as per figure (3) is taken, here the Edge preparation process is modified to double the groove instead of a single groove as shown in figure (3), while other parameters like groove angle, root face and root gap is maintained as per figure (1). Here results were although satisfactory, the inside groove depth (a) was however found to be more than 10 mm. A Magnetic Particle Inspection (MPI) at its root after back grinding from an outer circumference of the support shell (2), still detected the defect up to a depth of 6 mm maximum. So, to overcome this difficulty as well as to provide a full proof design, an edge preparation process as per figure (4) is taken for weldment. In this case, the inside groove depth is

6 mm, which exhibited a sound weldment, which was verified by conducting a mechanical testing and NDT.
During welding, following sequence has been followed. First, the SMAW welding should be done inside of the shell. Then back grinding / back gouging is done from outside circumference of the support shell (2). Third, MPI / LPI is conducted in the root layer from the outside surface shell. Then second layer weld is proceeded, then again MPI is conducted. Finally remaining groove is filled by SMAW process. This groove design weldment ensures soundness of the weldment.
The details of the experiment derived nomenclature is given in the following table.

*Angle has tolerance of upper limit +5mm, lower limit -0mm

WE CLAIM:
1. An edge preparation method and welding of a main plate with a support shell of a lifting attachment assembly to lift steam generators, comprising the steps of:
positioning the main plate (1) upto the water level of the generator and mounting the support Shell (2) over the main plate (1), wherein the edge preparation of the support shell (2) by generating an internal groove at 40° groove angle on the outer side of the support shell (2) at a horizontal distance maintaining horizontally the root face at about 25% of the total distance and the remaining horizontal distance of 75% being used for chamfering at an angle of 40°; maintaining a root gap of 1 to 3.5 mm (vertical distance) between the main plate (1) and the support shell (2);
initially conducting a first layer of SMW welding inside the shell, followed by back grinding / back gouging from outside circumference of the support shell (2);
conducting a magnetic particle inspecting (MPI) in the root layer from
outside tine surface shell;
conducting a second layer of welding including (MPI); and
filling the remaining groove by conventional SMAW process.