FIELD OF THE INVENTION
The present invention relates to an improved welding process to reduce welding
induced distortion during fabrication of a hydro turbine component involving
circumferential grooved fillet welding.
BACKGROUND OF THE INVENTION
Hydro turbine components are generally fabricated by welding and are made of
materials mainly belonging to the stainless steel category. Stainless steel
materials are heat sensitive materials that have higher coefficient of thermal
expansion compared to mild steels. Owing to the higher coefficient of thermal
expansion, the heating and cooling effects associated with welding leads to
change of shape and dimensions which is commonly referred to as welding
induced distortion. Once the components become distorted, some correcting
methods may have to be resorted to, in order to bring the component back to
the original geometry and dimensions. For this purpose, we have to add heat at
localized spots and this may induce some metallurgical damage in stainless steel
like it may lead to chromium depletion in heat exposed areas etc. Thus, during
welding of stainless steel components, extreme care and caution is to be
exercised in order to control welding induced distortion. This welding distortion
can only be controlled by the application of some procedures and this cannot be
eliminated completely. One effective way of controlling distortion is by using a
suitable welding technique which will, to a large extent, control the distortion

happening as a result of welding. Such welding techniques are case-specific and
have to be developed keeping into consideration the material nature and the
component geometry. Further, the welding techniques cannot be generalized
and have to developed by the welding engineer for different configurations of
the component with different design of weld joints and weld locations.
In the present invention, the authors provide a welding technique, which is
applicable to components involving welding of circumferential grooved fillet
welds in general and in particular, a welding technique for the fabrication of
hydro-turbine components. The detailed method of sequencing the weld layers in
a hydro-turbine component called as labyrinth has been disclosed in this
invention.
US patent 6307178 Bl relates to a method for welding shaped bodies of
carburized heat-resistant austenitic steel where the carburized steel parts to be
welded are preheated to temperatures of 700 to 900 degrees Celsius before
welding, and then the preheated carburized steel parts are welded with current
intensities of 50 to 200 A. But our invention deals with a method of sequencing
and laying the weld beads in a hydro-turbine component made of martensitic
stainless steel.
US patent 5591363 describes a process of depositing layers of weld metal onto a
ferrous NiMoV low alloy steel turbine component, where during the deposition of
a first layer of weld metal, low levels of amperage are used to prevent a

dramatic increase in a level of hardness of the HAZ and during the deposition of
a second layer of weld metal, higher levels of amperage are used to temper the
heat affected zone. But, our invention relates to the method of laying weld beads
in a sequential manner in a hydro-turbine component made of martensitic grade
of stainless steel with the primary aim of controlling welding induced distortion.
US patent 7703660 B2 refers to a method of determination by numerical
modeling and application of an optimum welding sequence that reduces the
welding induced distortion and residual stress formation while depositing hard-
facing layers on a boiler water wall panel. Our invention is different in the sense
that it is concerned with the method of sequentially laying welds in
circumferential grooved fillet weld of a hydro-turbine component called as
labyrinth made of martensitic stainless steel.
US patent US 6023044 discusses a control method in a multi-layer welding where
the weld line and a gap width of work pieces to be welded are detected by a
laser sensor mounted on a robot, during a welding for a first layer and welding
conditions are adjusted in accordance with the detected gap width for a second
and subsequent layer and performed by using the stored data in such a manner
that the welding torch is made to follow the weld line, and the welding conditions
are adjusted in accordance with the gap width. But, in our invention, a method
of sequencing weld beads during circumferential grooved fillet welding of hydro-
turbine components has been discussed in detail.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved welding process
to reduce welding induced distortion during fabrication of a hydro turbine
component involving circumferential grooved fillet welding.
Another object of the invention is to propose an improved welding process to
reduce welding induced distortion during fabrication of a hydro turbine
component involving circumferential grooved fillet welding, in which weld beads
in the weld groove are deposited sequentially, the weld being made in
martensitic stainless steel.
SUMMARY OF THE INVENTION
According to the invention, a method of application of a weld sequence to a
hydro-turbine component called as labyrinth that involves the welding of a
circumferential grooved fillet weld is disclosed. The labyrinth is made of
martensitic grade of stainless steel and is prone to severe welding induced
distortion, if not welded with a suitable sequence of depositing weld beads. The
method of laying the weld beads in a sequential manner in the circumferential
grooved fillet weld is explained in this invention.
The invention relates to the method of laying in a sequential manner, the weld
layers during the welding of the circumferential grooved fillet welding of a
labyrinth assembly that consists of a ring and a flange. The bottom edge of the
ring is suitably edge prepared into one of the available type of edge preparation

styles like the 'J', 'bevel' etc. depending on the strength requirements of the
labyrinth assembly. The edge preparation in the ring is done both on the Inner
Diameter (ID) side and in the Outer Diameter (OD) side as well. This edge
preparation may be done based on whether a partial penetration of weld is to be
achieved or a full penetration is to be achieved. The edge prepared ring is then
placed onto the flange in such a manner that a grooved fillet weld is required to
be carried out. After placement of the ring onto the flange, the welding method
to be adopted with a suitable sequence for both the ID side and OD side welding
is furnished in detail.
The labyrinth assembly is fabricated by welding a ring and a flange together.
These rings and flanges are made of martensitic stainless steel grade 410. The
ring is initially machined both on the ID and OD side and proper diameter and
thickness as desired is maintained.
Then, the bottom edge of the ring is edge prepared both in the ID side and in
the OD side. The flange of required diameter and thickness is taken. The ring is
then placed vertically over the flange. The Gas Metal Arc Welding process or the
CO2 welding process may be used for depositing weld in the circumferential
grooved fillet joint. Alternately, the shielded metal arc welding process may also
be used. After this assembly of the ring and flange is tack welded all along the
circumference at regular places. Then the full welding is commenced by
deploying either two welders simultaneously or single welder at a time. The
circumference of the labyrinth is divided into four equally spaced points. The

circumferential welding of the grooved fillet joint between the ring and the flange
is carried out alternately in the ID side and the OD side as described hereunder.
The Root weld layer is begun on the ID side and is completed. Subsequently,
two more weld layers are completed on the ID side itself. Then, back grinding is
done at the OD side and subsequently the non-destructive penetrant test is
carried out to check for defects in welding at the root layer. Thereafter, six
numbers of weld layers are filled on the OD side. The remaining weld layers are
completed on the ID side followed by completion of welding with requisite
number of weld layers on the OD side. Each of the weld layers mentioned
hitherto including the root and subsequent two layers laid in the ID side of the
labyrinth assembly are done using the weld sequence as detailed below
If a single welder is employed for welding, then the initial root layer of weld is
commenced from one of those points that are marked on the circumference of
the flange of the labyrinth in order to divide that into four equal parts. The
welding so commenced is continued along the groove formed between the ring
and the flange in a clockwise manner and completed after reaching the same
point. This forms one complete layer of weld. In some cases, additional weld
passes may be required to complete one layer of weld. The next weld layer is
commenced from that point, which lies diametrically opposite to the point from
where the first layer of weld was commenced. Then this second layer of weld is
continued in a clockwise direction and is completed at the same point where this
layer of weld was begun. The next weld layer is started from another point that

is 90 degrees away in the clockwise manner, from that point, where the previous
layer was commenced. This layer of weld is then deposited along clockwise
direction and is completed at the same point. The next layer is started from that
point, which lies diametrically opposite to the point, where the previous weld
layer was commenced. Again, this layer of weld also is completed after welding
all along the grooved and ended at the same point.
In case, two welders are deployed for welding, the first welder starts the welding
from one of those points that was marked on the circumference of the flange of
the labyrinth in order to divide that into four equal parts. At this instant when the
first welder starts welding, the second welder commences welding from the point
that is diametrically opposite to the point, where the first welder commenced
welding. The first welder and second welder continue depositing weld layer in
synchronization in a clockwise manner. By this way, one complete layer of weld
is completed. Next, the first welder starts welding from the point that is 90
degrees away, in the clockwise manner, from that point, where he has
commenced the previous weld layer. At this instant, the second welder
commences welding from the diametrically opposite point. Both the welders
proceed in an anti-clockwise direction and the weld layer is completed.
Thereafter, the subsequent weld layers are alternately deposited using the first
and second set of points. Prior to commencing the circumferential grooved fillet
welding of the ring to flange joint of the labyrinth, the reference points that are
equally spaced and are numbered from 1 through 4 and these points are marked

in paint on the actual component so as to enable the welders to carry out the
sequential welding as detailed hitherto.
The method of welding according to the invention comprising laying the weld
layers in sequential manner for welding of circumferential grooved fillet joints of
hydro-turbine components that consists of a minimum of one ring placed
vertically onto a flange. It is applicable for all sizes of rings and flanges of all
hydro turbine components having a minimum of one circumferential grooved
fillet weld. This weld sequence technique is also applicable for those components
where, a plurality of concentric rings is placed in the same flange with multiple
circumferential grooved fillet weld joints.
The method of welding is not necessarily manual. This weld sequence technique
can be applied even in semi-automatic or fully automated welding methods using
programmed robots as well. The material of the hydro-turbine component is not
limited to martensitic stainless steel and the material is not a limiting factor for
the use of this technique. The weld sequence technique disclosed in this
invention can also be used for other hydro-turbine materials. The variables of
welding process used like speed of deposition of weld layer, welding current, arc
voltage etc. are not a limiting factor for the application of the said weld
sequencing technique to weld hydro-turbine components. The position of
welding like 1G, 2G etc. is not a limiting factor for the application of the said
technique and is covered within the scope of the invention. The use of
accessories like a rotating positioner is not excluded from the scope of the

invention. The said weld layer sequencing technique can be employed with or
without the use of such accessories. The number of welders employed for
applying the said weld layer sequencing technique is not a limiting factor for its
use. The number of divisions made circumferentially in the flange for selecting
the segments that are to be welded sequentially is not limited to four, it can be
decreased or increased and such modifications are covered within the scope of
the invention.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Ring and flange fitted together to form labyrinth assembly containing
the circumferential grooved fillet joint.
Figure 2 - cross sectional view of the circumferential grooved fillet joint between
the ring and flange.
Figure 3 - Schematic sketch of weld sequence followed for labyrinth welding and
the circumferential division of labyrinth into four equally spaced points as seen
from top view.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
According to the invention, there is disclosed a method for depositing weld layers
in a sequential manner, in the circumferential grooved fillet joint formed between
a ring and a flange that forms the labyrinth assembly of the hydro-turbine, in

order to minimize the welding induced distortion. The ring and flange are made
of 410 grade of martensitic stainless steel.
The labyrinth is a hydro-turbine component that contains a ring and a flange that
are welded together. The ring and the flange are made of martensitic stainless
steel, which by virtue of the higher coefficient of thermal expansion results in
heavy distortion after fabrication by welding. There is provided a method in this
invention to deposit the weld layers in a sequential manner that would minimize
the welding induced distortion during the welding of circumferential grooved fillet
joint between the ring and the flange of the labyrinth assembly.
The ring is machined and brought to the required dimensions of outer diameter
(OD), Inner Diameter (ID) and thickness. The bottom edge of the ring (1) is
beveled and the edge is prepared for facilitating the weld groove where the weld
metal will be deposited. The edge preparation is done both in ID side as well as
in OD side. The type of edge preparation may be a 'J', 'V' etc. depending on the
strength levels of the joint required. The flange (2) is taken and is machined and
brought to the required diameter and thickness. Thereafter the ring (1) is placed
vertically onto the flange(2) as shown in the figure 1 and the fit-up is done by
placing tack welds of length not less than 50 mm in a minimum of ten locations
spread across the circumference of the flange. It is to be ensured that during the
tack welding and during subsequent welding, the preheating and inter-pass
temperatures as recommended by the WPS (Welding Procedure Sheet) are to be
maintained. After placing the ring onto the flange, the grooved fillet joints in the

OD side (3) and ID side (4) are the areas where the weld metal is to be
deposited. A cut sectional view of the labyrinth assembly consisting of the ring
and flange is shown in figure (2) where the weld joint details in the ID side (4)
and OD side (3) are clearly seen. This labyrinth assembly consisting of the ring
and flange is welded using one of the available welding processes like Gas Metal
Arc Welding (GMAW), CO2 welding, Submerged arc welding (SAW) or the
conventional Shielded Metal Arc Welding (SMAW). The welding process to be
chosen is matter of choice of the designer based on the strength and productivity
requirements. After completion of tack welding, with the required level of
preheat, the welding of the component is commenced with the following
procedure.
The circumferential welding of the grooved fillet joint between the ring and the
flange is carried out alternately in the ID side (4) and the OD side (3) as shown
in figure 1. The first layer of weld deposited is normally termed as the root layer.
This root layer of weld is begun on the ID side and this layer is fully completed.
It may take more than one pass for completion of one weld layer depending on
the groove configuration. The subsequent two weld layers are completed in ID
side itself. If necessary, more than one pass may be deposited based on the joint
configuration for these weld layers. Then, back grinding is done at the OD side
and subsequently the liquid penetrant testing is done to check for the presence
of any weld defects. If weld defects are found, then they have to be ground and
removed. Thereafter, six numbers of weld layers are deposited in the OD side.

For each of these layers, multiple weld passes as found necessary are deposited.
The remaining weld layers are completed on the ID side followed by completion
of remaining weld layers in the OD side. If the weld layers required in the ID side
and OD side of the labyrinth in the circumferential grooved fillet joint is lesser
than six, then the number of weld layers deposited in the ID side and in the OD
side is approximately kept in the ratio 1:3. All the weld layers mentioned above
including the root and subsequent two layers deposited in the ID side are to be
done using the weld sequence as detailed below:
Each layer of weld in the circumferential grooved fillet joint between the ring (1)
and the flange (2) can be accomplished by deploying either a single welder or
using two welders both engaged simultaneously. For this purpose, the entire
circumference of the flange (2) is divided into 4 equally spaced points as shown
in figure 3. The points are numbered from 1 through 4.The points are marked
with paint in the flange in order to make it easier for the welders to the follow
the welding procedure. The welding sequence and the procedure using single
welder and two welders are given in detail hereunder.
Single welder approach:
1) If a single welder is employed, the first weld layer is commenced by the
welder from the point 1 (as seen in figure 3) and is continued circumferentially in
a clockwise direction and ended at the same point 1 thus forming a complete
layer of weld.

2) The next layer is commenced from point 2, which is diametrically opposite to
point 1, where the first layer of weld was begun and is continued in a clockwise
direction and completed at point 2, the starting point of this weld layer.
3) The next weld layer is started from point 3, which is 90 degrees away in the
clockwise direction from point 2, proceeded along anti-clockwise direction and is
completed at the same point 3. Similarly, the next weld layer is started from
point 4, the diametrically opposite point to point 3. This weld layer is continued
in the anticlockwise direction and ended at the same point 4.
Two welder approach:
1) If two welders are deployed for welding, the first welder begun depositing the
weld layer from the point 1 (as seen in figure 3) continued welding in the
clockwise direction until the point 2 is reached. The second welder commenced
welding from point 2 at the same instant, when the first welder started welding
from point 1. The second welder also continued depositing the weld layer in the
clockwise direction until the point 1 is reached. Thus one complete weld layer is
deposited in this manner by using two welders acting in tandem.
2) Thereafter, for depositing the subsequent weld layer, the first welder started
welding from the point 3, the point that is 90 degrees away from point 2 in the
clockwise manner. The weld layer is continued in the anticlockwise direction and
ended at the point 4. The second welder commenced depositing the weld layer
from point 4 at the same instant, when the first welder started welding from

point 3. The second welder continued welding along the anticlockwise direction
and ended at the same point 3.
3) With reference to figure 3, the points 1 and 2 form the first set and points 3
and 4 forms the second set. Whenever a layer of weld is completed using first
set of points in the clockwise direction, the subsequent layer of weld is deposited
using the second set of points in the anti-clockwise direction. Such layers of weld
are deposited simultaneously by deploying two welders starting and ending in
diametrically opposite points. Thereafter, the subsequent layers are alternately
deposited using the first and second set of points by reversing the direction of
deposition of deposition of weld layer. In this manner, the labyrinth assembly
having a circumferential grooved fillet joint between the ring and the flange is
welded.
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.

WE CLAIM
1. An improved welding process to reduce welding induced distortion during
fabrication of a hydro turbine component involving circumferential
grooved fillet welding, the turbine component constituting a labyrinth
consisting of at least one each flange and ring welded together by a
circumferential grooved fillet joint, the method comprising the steps of:
- sequentially depositing weld both in an inner and outer diameter
sides of the groove;
- carrying out back grinding step on the outside diameter side; and
- determining presence or otherwise of defects on the weld through
conducting liquid penetrant test.

2. The method as claimed in claim 1, wherein the root weld layer and two
subsequent layers are deposited in the internal diameter side.
3. The method as claimed in claim 1, wherein the flange is virtually
segmented into four equally spaced points, and wherein each layer
starting from a fixed point and circumferentially proceded to end at that
fixed point.
4. The method as claimed in claim 1, wherein the third layer is started from
a point that is spaced 90 degrees in anticlockwise direction from the fixed
point from which the first layer had started.

ABSTRACT

The present invention relates to an improved welding process to reduce welding
induced distortion during fabrication of a hydro turbine component involving
circumferential grooved fillet welding, the turbine component constituting a
labyrinth consisting of at least one each flange and ring welded together by a
circumferential grooved fillet joint, the method comprising the steps of:
sequentially depositing weld both in an inner and outer diameter sides of the
groove; carrying out back grinding step on the outside diameter side; and
determining presence or otherwise of defects on the weld through conducting
liquid penetrant test.