FIELD OF INVENTION
The present invention relates to an improved method of edge preparation (EP) of
header pipes for welding with plug type end covers and machining of additional
thickness. More particularly, the invention relates to Edge Preparation (EP) of the
Header Pipes of Alloy Steel used in Steam Generators. This invention further relates to
machining and fabrication of plug type end covers (PEC) used in Super Heaters and Re-
heaters of High temperature, High Pressure boilers.
BACKGROUND OF THE INVENTION
Normally Super Heaters, Re-Heaters, Economizers have headers with Plugs
either on one or both sides. These plugs have thickness ranging from 80mm to 162mm
and are welded with the Header Pipes having OD ranging from D273mm to D762mm.
The thickness of Header pipes ranges from 30mm to 124mm. The present EP on the
pipe is complicated and defects are exhibited after welding. In particular, lack of fusion
observed during Non-Destructive examination - Ultrasonic Testing is the common defect
which needs material removal by machining or grinding from the root of the joint
through back side opening in a pipe, which involves more time and rework and also non
visible for this operation due to existing EP design.

The positioning of the PEC is also a cumbersome process, considering the weight
of the end cover, which ranges from 22Kg to 450Kg and its non-uniform seating for
3mm width around 360°, which results in uneven shrinking and post weld distortion.
Referring to fig.1 the PEC (01) has thickness ranging from 30mm to 162mm with
EP of 30° for 38mm and 10° for the remaining thickness of the PEC.
Referring to fig 2, the EP was carried out in the Header pipe (02) so that there
will be overlapping of 3mm all around the step provided while placing the PEC on the
Header Pipe as shown in Fig 3. This overlapping 3mm which creates lack of fusion after
welding needs further study.
Therefore, there is a need to find out an alternative design in the pipe material
to overcome the above drawbacks.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose an improved method of
edge preparation of header pipes for welding with plug type end covers and machining
of additional thickness, which is capable of a suitable modification in the plug type end
cover to perfectly seat on a modified Header pipe.

Another object of the invention is to propose an improved method of edge
preparation of header pipes for welding with plug type end covers and machining of
additional thickness that involves an increase of thickness of plug type end cover in
accordance with the depth of additional step provided in the header pipe.
A still another object of the invention is to propose an improved method of edge
preparation of header pipes for welding with plug type end covers and machining of
additional thickness, which involves introduction of an additional small step in the
header pipe in addition to the already available step in the header pipe edge
preparation along with a marginal decrease in internal diameter.
A further object of the invention is to propose an improved method of edge
preparation of header pipes for welding with plug type end covers and machining of
additional thickness, which is capable of ensuring perfect seating of the plug type end
cover concentrically on the header pipe end paving the way for uniform fusion.
A still further object of the invention is to propose an improved method of edge
preparation of header pipes for welding with plug type end covers and machining of
additional thickness, which allows welding to be carried out with minimum current
resulting better control while welding.

SUMMARY OF THE INVENTION
Accordingly, a small step is introduced in the header pipe in addition to the
already available step in the header pipe Edge Preparation along with a marginal
decrease in ID.
The thickness of the Plug-Type End Cover is also increased in accordance with
the depth of the addition step provided in the Header Pipe.
This ensures perfect seating of the Plug-Type End Cover concentrically on the
header pipe end and also paves the way for uniform fusion.
Now the welding is carried out with minimum current and thereby better control
while welding.
This additional step in the header pipe provides perfect seating of the PEC and
hence there is no movement of the PEC on any side and concentricity is maintained
throughout the process.
Now machining is adopted from back side of pipe to remove the unfused layer in
the pipe and plug end cover joint if any and maintain the design dimensions. This
removes any unfused layer between the two objects resulting in completely fused layers
thereby eliminating the defects mentioned in the background such as lack of fusion
while testing with Non-Destructive examination – Ultrasonic Testing.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 Shows the existing Plug-type end cover (01).
Fig 2 Shows the existing edge preparation in Header pipe (02).
Fig 3 Shows the existing assembly of the item numbers 01 and 02.
Fig 4 Shows the detailed view of the item numbers 01 and 02 showing the
overlap with much clarity.
Fig 5 Shows the Plug-type end cover (03) with additional thickness and reduced
diameter.
Fig 6 Shows the edge preparation in Header pipe (04) with additional step in
the design with additional thickness on the sides.
Fig 7 Shows the assembly of item numbers 03 and 04 after modification.
Fig 8 Shows the detailed view of the items 03 and 04 showing the additional
step of 2mm.
Fig 9 Shows a better control while welding when root welding is carried out
using Tungsten inert gas welding process with minimum current.
Fig 10 Shows the marked area for machining to remove the additional thickness
in both the components.
Fig 11 Shows assembly of the two components after meeting the final design
requirement after back-machining.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
In addition to the step already available in Header Pipe (02 in Fig 2), while
maintaining higher thickness than required a small step is introduced in the header pipe
(04 in Fig 6) tapered down from the earlier step at an angle for welding approach.
The thickness of the Plug-Type End Cover is also increased (03 in Fig 5) in
accordance with the depth of the addition step provided in the Header Pipe (04 in Fig
6). The Diameter is also slightly reduced to match with the increase in thickness of the
Header Pipe (04 in Fig 6).
This ensures perfect seating of the Plug-Type End Cover (03) concentrically on
the header pipe end (04) as shown in Fig 7 and Fig 8 and also paves the way for better
root fusion due to sharper contact between pipe and plug-type end cover.
The Depth of the additional step in Header Pipe (04) and the corresponding
increase in the thickness of Plug-type End Cover (03) has been experimentally found
out to be 2mm. Hence, a step of 2mm is provided in addition to the step available in
Edge preparation of Header Pipe (04). The thickness of plug-type End Cover (03) is

increased by 2mm so as to seat perfectly on the Header Pipe (04) maintained with
higher thickness. By the above means the horizontal movement on the X direction and
Y direction are arrested for the Plug-type End Cover (03) in the Header pipe (04).
Now the root welding is carried out using Tungsten Inert Gas Welding process
with minimum current and thereby better control while welding as shown in Fig 9.
Further layers can be welded using Shielded Metal Arc Welding manually or using
Submerged Arc Welding to save cycle time.
After Post weld heat treatment, the Pipe (03) with Plug Type End Cover (04)
arrangement will be back-machined for the area marked in Fig 10 to remove the
additional thickness in both the components. Since the overlap portion was present in
the additional thickness, the same has been removed while machining thereby ruling
out any root lack of fusion defect.
Fig 11 shows the assembly with dimensions meeting the final design requirement
after back-machining.

WE CLAIM
1. An improved method of edge preparation of header pipes for welding with plug
type end covers and machining of additional thickness, the said method comprising the
steps of;
providing a step of 2mm in the header pipe (04) in addition to the step already
available (02) in the edge preparation of said header pipe;
providing an increase of 2mm in the thickness of the plug-type end cover (03)
resulting the diameter of the plug-type end cover slightly reduced to match with the
increase in thickness of the header pipe (04) wherein, the plug type end cover (03) sits
perfectly and concentrically on the header pipe end (03, 04) arresting the horizontal
movement on the X direction and Y direction for the plug type end cover (03) in the
header pipe (04) and to create better root fusion due to sharper contact between pipe
and plug-type end cover, wherein root welding is carried out by Tungsten inert gas
welding process with minimum current for a better control of welding when final
welding layers being carried out with shielded metal arc welding or submerged arc
welding when after a post weld heat treatment, additional thickness in both the
components that includes overlapping portion, is removed after machining to maintain
the designed dimension eliminating any non-fused portion.