FIELD OF INVENTION
[001] The present invention relates to a method for welding a three-piece safety valve
for ultra-super critical boiler applications. The present invention is also related to a
welding procedure and optimizing parameters for three-piece safety valve of steel
forging, Inconel Alloy and Stainless steel material using shielded metal arc welding
(SMAW) process.
BACKGROUND/PRIOR ART OF THE INVENTION
[002] A welding technique for three-piece safety valve for steam service in high
pressure and high temperature pressure vessel application. This safety valve needs to
comply the Indian Boiler Regulations and ASME Sec-l, Rules for construction of
Power Boiler. The device operates during closing on a back pressure principle, that is,
the force of trapped steam on the upper side of the holder is utilized to assist a spring
of the device in forcing the closing element back down onto its seat. The safety valve
designed for high pressure and high temperature up to 620oC. These valves are
intended for Super Heater and Hot Re-Heater applications. The materials used in
safety valve are base stainless steel, seat bushing Inconel Alloy 617 and inlet neck F92
alloy, which are to be integrated by dissimilar material welding.
[003] Welding of dissimilar materials, i.e., grade 92 steel with Ni-base Alloy 617 and
stainless steel CF8M super alloys becomes inevitable. Further, post weld heat
treatment temperature of alloy 617 and grade 91 has huge difference, which makes
this dissimilar jointing process highly difficult. Hence, it is proposed to develop
welding sequence between grade 92 steel, Alloy 617 (Ni-base super alloy) and
Stainless Steel CF8M material for 3 –piece safety valve applications using weld
buttering technique in Ultra Super Critical (USC) power plants where steam
temperatures of weldment will be around 620oC.

[004] Existing prior art such as US6753504B2 describes about a procedure for
welding a Ni-base super alloy with a steel was explained. In this patent joining was
carried out by having an intermediate layer (IN 617) on the Ni-base super alloy (IN
625 containing Nb which leads to weld solidification cracking) and then joining this
to the steel using Metal Active Gas process or Tungsten Inert Gas welding process.
This is employed for obtaining crack-free welded rotors for turbo-machinery
applications.
[005] Another prior art US20120301309A1 describes about a procedure for
obtaining dissimilar metal welds using buttering technique is discussed in detail for
applications related to welding large components such as turbine rotor. In the method
disclosed by this patent application, dilution ratio of buttering layer to metal is less
than 50%. This can be employed for welding large components such as turbine rotor.
[006] Another prior art US8308051B2 describes about the welding method for
welding dissimilar metals (i.e., one high melting point material with one lower melting
point material) were discussed using friction stir welding process. The method
involves presence of rotary tool which makes the interface softer and later joins them
to obtain a sound weld joint. Joints between steel and aluminium were successfully
obtained using this technique.
[007] Another prior art US200880067214A1 describes about the method of having a
transition for superheater or reheater tubes by mechanical forming and hot isostatic
pressing (HIP) is discussed. This method eliminates the need for arc welding or other
fusion welding processes. The transition is from ferritic T11 or T22 steel (ASME A213
type) to TP347 or TP 304 type austenitic steels (which resist higher temperatures).

[008] Another prior art WO2001083151A1 application discusses joining dissimilar
metals such as steels and aluminium using new technique. In this invention,
Aluminium is retrogressively heat treated locally at the joint prior to electromagnetic
forming (EMF) or magnetic pulse welding (MPW). This technique led to development
of stronger welds.
[009] Another prior art EP2617512A1 discusses the procedure for producing weld
joints between Ni-base super alloy impeller and steel shaft. The welds are obtained by
fusing the metals (mixing ratio by weight) in the ratios of 0.5 to 0.8. The welds
obtained are sound and crack-free.
[0010] Thus the existing prior arts discuss about development of dissimilar metal
welds which are defect free. But the discussed methods are sophisticated techniques
such as HIP or EMF or MPW. None of them can employ techniques as such weld
buttering with ENiCrFe-3 electrode using shielded metal arc welding (SMAW) and
sequential post weld buttering heat treatment for dissimilar three-piece material weld
joint.
[0011] The present invention is directed to address the above problems and focus on
shielded metal arc welding (SMAW) employed using electrode for welding a three-
piece safety valve. Also the present invention uses sequential welding with heat
treatment cycle for obtaining defect free final weld between grade 92 steel, Alloy 617
materials and Stainless Steel CF8M.
OBJECTS OF THE INVENTION
[0012] It is therefore a principal object of the present invention to propose a method
of welding a three-piece safety valve using shielded metal arc welding process.

[0013] Another object of the present invention is to propose development of welding
procedure, heat treatment sequence and optimize parameters for producing defect free
weldments between grade 92 steel, Alloy 617 and Stainless steel CF8M with ENiCrFe-
3 electrode using shielded metal arc welding process.
[0014] These and other objects and advantages of the present subject matter will be
apparent to a person skilled in the art after consideration of the following detailed
description taken into consideration with accompanying drawings in which preferred
embodiments of the present subject matter are illustrated.
SUMMARY OF THE INVENTION
[0015] This summary is provided to introduce concepts relates to a welding procedure
and optimizing parameters for three-piece safety valve using shielded metal arc
welding (SMAW) consumable electrode.
[0016] The present invention is related to the method for welding a three-piece safety
valve for ultra-super critical boiler application, the method comprising the steps of:
preparing a furnace system comprising of at least one dissimilar metal having different
compositions and different welding temperature; welding the at least one dissimilar
metal using a welding electrode, buttering and inter-passing the three dissimilar metals
to achieve a desired thickness, heating the three dissimilar metals post to the buttering
with the inter-pass temperature maintained at a specified set level. Cooling the three
dissimilar metal weld, and forming a base, a seat bushing, an inlet neck and a joining
weld for the three-piece safety valve.
[0017] In an aspect of the invention, the welding at least one dissimilar metal by
exposing to a shielded metal arc welding and sequential welding with heat treatment
cycle for obtaining defect free weld. The inter-pass temperature maintained is 980°C

and the post weld heat treatment temperature is 760°C for three hours. Radiographic
testing the finished weld to verify the soundness.
[0018] In an aspect of the invention the three-piece safety valve designed to withstand
high pressure and high temperature up to 620oC. The at least one dissimilar metal is
selected from a group of Grade 92 steel, Inconel Alloy 617 and stainless steel
CF8M.The three-piece safety valve comprises of a base, a seat bushing and an inlet
neck.
[0019] In an aspect of the invention, edge preparation design is used for dissimilar
welding. The alloy 617 was weld buttered with ENiCrFe-3 using SMAW process for
specified thickness ‘A’. Then, Alloy 617 butter material is subjected to post buttering
heat treatment at the temperature and allowed cool inside the furnace. The Grade 92
welded to buttered alloy 617 material and stainless steel CF8M using same welding
consumable ENiCrFe-3.The final weld is subjected to post weld heat treatment
temperature and allowed cool inside the furnace for tempering of grade 92 steel heat
affected zone.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0020] It is to be noted, however, that the appended drawings illustrate only typical
embodiments of the present subject matter and are therefore not to be considered for
limiting of its scope, for the invention may admit to other equally effective
embodiments. The detailed description is described with reference to the
accompanying figures. In the figures, a reference number identifies the figure in which
the reference number first appears. The same numbers are used throughout the figures
to reference like features and components. Some embodiments of system or methods
or structure in accordance with embodiments of the present subject matter are now

described, by way of example, and with reference to the accompanying figures, in
which:
[0021] FIG. 1 shows an assembly of three-piece safety valve for ultra-super critical
boiler with inlet neck, seat bushing and base in accordance with the present invention;
[0022] FIG. 2 shows a weld buttering technique followed for seat bushing material
using shielded metal arc welding (SMAW) process and edge preparation followed for
final butt welding with steel in an embodiment of the present invention;
[0023] FIG. 3 shows an assembly of three-safety valve after full welding completion
using shielded metal arc welding (SMAW) process with ENiCrFe-3 electrode.
[0024] The figures depict embodiments of the present subject matter for the purposes
of illustration only. A person skilled in the art will easily recognize from the following
description that alternative embodiments of the structures and methods illustrated
herein may be employed without departing from the principles of the disclosure
described herein.
DETAIL DESCRIPTION OF INVENTION WITH REFERENCE TO THE
DRAWINGS OF THE PREFERRED EMBODIMENTS
[0025] While the embodiments of the disclosure are subject to various modifications
and alternative forms, specific embodiment thereof have been shown by way of
example in the figures and will be described below. It should be understood, however,
that it is not intended to limit the disclosure to the particular forms disclosed, but on
the contrary, the disclosure is to cover all modifications, equivalents, and alternative
falling within the scope of the disclosure.
[0026] The terms “comprises”, “comprising”, or any other variations thereof used in
the disclosure, are intended to cover a non-exclusive inclusion, such that a device,

system, assembly that comprises a list of components does not include only those
components but may include other components not expressly listed or inherent to such
system, or assembly, or device. In other words, one or more elements in a system or
device proceeded by “comprises… a” does not, without more constraints, preclude the
existence of other elements or additional elements in the system or device.
[0027] The present invention is related to the method for welding a three-piece safety
valve for ultra-super critical boiler application, the method comprising the steps of:
preparing a furnace system comprising of at least one dissimilar metal having different
compositions and different welding temperature; welding the at least one dissimilar
metal using a welding electrode, buttering and inter-passing the three dissimilar metals
to achieve a desired thickness, heating the three dissimilar metals post to the buttering
with the inter-pass temperature maintained at a specified set level; cooling the three
dissimilar metal weld; and radiographic testing the finished weld to verify the
soundness. The three-piece safety valve comprises a base (1), a seat bushing (2), an
inlet neck (3) and a joining weld (4). In a preferred embodiment, the joining weld (4)
is the deposited weld metal using welding consumable ENiCrFe-3 electrode and the
welding is done of at least one dissimilar metal by exposing to a shielded metal arc
welding and sequential welding with heat treatment cycle for obtaining defect free
weld.
[0028] FIG. 1 shows an assembly of three-piece safety valve for ultra-super critical
boiler with the inlet neck (3) Grade 92, the seat bushing (2) Alloy 617 and the base (1)
stainless steel CF8M in accordance with the present invention. In a preferred
embodiment the base (1) is made up of SA351 CF8M stainless steel materials. The
seat bushing (2) is made up of Inconel Alloy 617 and the inlet neck (3) is made up of
SA 182 F92. The filler material used for butt welding of the three-piece safety valve
is ENiCrFe-3 electrode. The chemical compositions of the base materials and the filler
material were measured by Optical Emission Spectrometry technique and all are

complied with the ASME specifications. The arrangement of edge machined
components before welding is shown in FIG. 1. The edge prepared grooves of grade
92 to alloy 617 and stainless steel CF8M material are butt welded with ENiCrFe-3
electrode using shielded metal arc welding (SMAW) process for full thickness and
subjected to post weld heat treatment (PWHT).
[0029] In a preferred embodiment the procedure for defect-free welding of Grade 92
steel with Alloy 617 and Stainless Steel CF8M using ENiCrFe-3 electrode is disclosed.
The shielded metal arc welding system uses buttering of seat bushing (2) material
Alloy 617 using ENiCrFe-3 electrode. The heat treatment sequence used for buttering
seat busing alloy 617 for making the three-piece safety valve joint with the limitation
of buttering thickness on alloy 617 and the joint design as shown in FIG. 1. Inter-pass
temperature is maintained at <150 ᵒC except for weld buttering on Alloy 617. The
Stainless steel wire brush is used for cleaning between passes and removes oxide
debris.
[0030] According to one embodiment, the Welding of grade 92 steel to Alloy 617 and
stainless steel CF8M as per procedure for direct application at sites (i.e) power plant
erection and commissioning areas. Also welding of grade 92 steel to Alloy 617 and
stainless steel CF8M as per procedure used for applications at shop floor
(manufacturing areas).
[0031] FIG. 2 shows a weld buttering technique followed for seat bushing (2) material
using SMAW process and edge preparation followed for final butt welding with steel
in an embodiment of the present invention. As illustrated in FIG. 2 the seat bushing
(2) Alloy 617 weld buttered using ENi CrFe-3 electrode with shielded metal arc
welding (SMAW) process for a specified thickness and subjected to post buttering
heat treatment at the temperature of 980°C for 3 hours and allowed to cool inside the
furnace for stress reliving purpose. Then seat bushing (2) alloy 617 is machined as

shown in FIG. 2 for butt welding with grade 92 and stainless steel CF8M material as
shown in FIG. 1.
[0032] In a preferred embodiment all the three pieces (after edges machined) are
assembled as shown in FIG. 1 and butt welded using shielded metal arc welding
(SMAW) process. The final finished three-piece safety valve is subjected to post weld
heat treatment temperature of 760°C for 3 hour and allowed to cool inside the furnace
for tempering of grade 92 steel heat affected zone.
[0033] In a preferred embodiment the welding process is applicable not only for safety
valve but also for tubes, pipe, forged sections, etc. where weldments of grade 92 steel,
Alloy 617 and Stainless steel are visualized. These weldments are used for ultra-super
critical (USC) power plant component applications.
[0034] FIG. 3 shows an assembly of three-safety valve after full welding completion
using SMAW process with ENiCrFe-3 electrode. In a preferred embodiment between
passes, the material is cleaned using acetone followed by using stainless steel wire-
brush to remove any inter-pass oxides. Optimized welding parameters which are
established during procedure qualification are used for welding the three-piece safety
valve to avoid defects like porosity, lack of fusion, weld depression, etc. The finished
welds are subjected to radiographic testing to verify the soundness of the joint. The
conventional shielded metal Arc welding with parameters are mentioned in Table 1.
The seat bushing (3) alone undergo post weld heat treatment (PWHT) at 980±10°C
after weld buttering. After full welding, the joint (all three pieces together) undergo
PWHT at 760±10°C. Also the optimized parameters employed during welding are
indicated in Table 1. Tensile Test Results of three piece welding safety valve at Room
Temperature (25ᵒC) are indicated in Table 2. In a preferred embodiment a total of ~52
layers are used to successfully complete the welding.

Table 1: Optimized welding parameters employed during welding three-piece safety
valve using SMAW process.

Welding parameter Details

Weld Buttering Butt weld
Welding Process SMAW SMAW
Electrode Size Ø3.15 mm Ø2.5 mm, Ø3.15 mm & Ø4.0 mm
Preheat Temperature Nil 220ᵒC
Current 109 A 75 -143 A
Voltage 21V 20-25V
Interpass Temperature <150ᵒC <350ᵒC
Travel Speed 91 mm/minute 70-130 mm/minute
Bead Type Stringer Stringer & Weave
Table 2: Tensile Test Results of three piece welding safety valve at Room Temperature
(25ᵒC).

Sl. No 0.2% UTS %E %RA Place of
YS
(MPa) (MPa) Failure
1 455 625 25 41 Weld Metal
[0035] In a preferred embodiment, edge preparation design as shown in Fig. 1 has to
be followed for dissimilar welding. The alloy 617 was weld buttered with ENiCrFe-3
using SMAW process for specified thickness ‘A’ as shown in Fig. 2. Then, Alloy 617
butter material is subjected to post buttering heat treatment at the temperature of 980°C
for 3 hours and allowed to cool inside the furnace for stress reliving purpose.

Thereafter Grade 92 is welded to buttered alloy 617 material and stainless steel CF8M
using same welding consumable ENiCrFe-3 as per Fig. 3. The final welding subjected
to post weld heat treatment temperature of 760°C for 3 hours and allowed to cool
inside the furnace for tempering of grade 92 steel heat affected zone.
[0036] The materials are given as example without restricting scope of the invention
to the same. Thus, other materials readily apparent to a person skilled in the art are
understood to be within purview of the invention.
[0037] The present invention three-piece safety valve welding procedure for
producing welds of grade 92 steel (SA 182 F92) to Alloy 617 (SB 564 UNS N06617)
and Stainless Steel SA 351 CF8M of approx. 60 mm thickness using ENiCrFe-3
welding electrode employing shielded metal arc welding is developed and
investigated. The three-piece safety valve welding procedure reduces the distortion
and residual stress formation during the heat treatment sequence. Prior to the welding
of the actual three-piece safety valve, optimization of parameters and welding
procedure developed as per ASME Sec IX. The test coupons were subjected to
radiographic testing and followed by mechanical tests viz. tensile test and 180ᵒ bend
testing are carried out as per ASME welding procedure qualifications. Using the three-
piece safety valve welding procedure no cracks are observed after carrying out bend
testing, thereby, qualifying the procedure. The finalized welding parameters along
with the developed joint design for three-piece safety valve is observed. The present
invention is useful for producing defect free weldments at regions where steam passes
reach 6200C for components of ultra-super critical (USC) power plants.
[0038] According to the present invention, the welding procedure with optimized
welding parameters was developed for obtaining dissimilar welds of grade 92 steel,
Alloy 617 and Stainless Steel CF8M with ENiCrFe-3 electrode using shielded metal
arc welding (SMAW) process. For an example the welding method was carried out for

10 pairs of safety valves which are successfully welded using the procedure disclosed
in the present invention. The welding method of the present invention improves
reproducibility. The weldments produced as a result of this welding procedure has
qualified tensile tests and side bend tests without showing up any cracks.
[0039] It should be noted that the description and figures merely illustrate the
principles of the present subject matter. It should be appreciated by those skilled in the
art that conception and specific embodiment disclosed may be readily utilized as a
basis for modifying or designing other structures for carrying out the same purposes
of the present subject matter. It should also be appreciated by those skilled in the art
that by devising various arrangements that, although not explicitly described or shown
herein, embody the principles of the present subject matter. Furthermore, all examples
recited herein are principally intended expressly to be for pedagogical purposes to aid
the reader in understanding the principles of the present subject matter and the
concepts contributed by the inventor(s) to furthering the art and are to be construed as
being without limitation to such specifically recited examples and conditions. The
novel features which are believed to be characteristic of the present subject matter,
both as to its organization and method of operation, together with further objects and
advantages will be better understood from the following description when considered
in connection with the accompanying figures.
[0040] These and other advantages of the present subject matter would be described
in greater detail with reference to the following figures. It should be noted that the
description merely illustrates the principles of the present subject matter. It will thus
be appreciated that those skilled in the art will be able to devise various arrangements
that, although not explicitly described herein, embody the principles of the present
subject matter and are included within its scope. The present invention will now be
described more specifically with reference to the following specification.

[0041] It should be noted that the description and figures merely illustrate the
principles of the present subject matter. It should be appreciated by those skilled in the
art that conception and specific embodiment disclosed may be readily utilized as a
basis for modifying or designing other structures for carrying out the same purposes
of the present subject matter. It should also be appreciated by those skilled in the art
that by devising various arrangements that, although not explicitly described or shown
herein, embody the principles of the present subject matter and are included within its
spirit and scope. Furthermore, all examples recited herein are principally intended
expressly to be for pedagogical purposes to aid the reader in understanding the
principles of the present subject matter and the concepts contributed by the inventor(s)
to furthering the art and are to be construed as being without limitation to such
specifically recited examples and conditions. The novel features which are believed to
be characteristic of the present subject matter, both as to its organization and method
of operation, together with further objects and advantages will be better understood
from the following description when considered in connection with the accompanying
figures.
[0042] Although embodiments for the present subject matter have been described in
language specific to package features, it is to be understood that the present subject
matter is not necessarily limited to the specific features described. Rather, the specific
features and methods are disclosed as embodiments for the present subject matter.
Numerous modifications and adaptations of the system/device of the present invention
will be apparent to those skilled in the art, and thus it is intended by the appended
claims to cover all such modifications and adaptations which fall within the scope of
the present subject matter.
[0043] It will be understood by those within the art that, in general, terms used herein,
and especially in the appended claims (e.g., bodies of the appended claims) are
generally intended as “open” terms (e.g., the term “including” should be interpreted as

“including but not limited to,” the term “having” should be interpreted as “having at
least,” the term “includes” should be interpreted as “includes but is not limited to,”
etc.). It will be further understood by those within the art that if a specific number of
an introduced claim recitation is intended, such an intent will be explicitly recited in
the claim, and in the absence of such recitation no such intent is present. For example,
as an aid to understanding, the following appended claims may contain usage of the
introductory phrases “at least one” and “one or more” to introduce claim recitations.
However, the use of such phrases should not be construed to imply that the
introduction of a claim recitation by the indefinite articles “a” or “an” limits any
particular claim containing such introduced claim recitation to inventions containing
only one such recitation, even when the same claim includes the introductory phrases
“one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a”
and/or “an” should typically be interpreted to mean “at least one” or “one or more”);
the same holds true for the use of definite articles used to introduce claim recitations.
In addition, even if a specific number of an introduced claim recitation is explicitly
recited, those skilled in the art will recognize that such recitation should typically be
interpreted to mean at least the recited number (e.g., the bare recitation of “two
recitations,” without other modifiers, typically means at least two recitations, or two
or more recitations). Furthermore, in those instances where a convention analogous to
“at least one of A, B, and C, etc.” is used, in general such a construction is intended in
the sense one having skill in the art would understand the convention (e.g., “a system
having at least one of A, B, and C” would include but not be limited to systems that
have A alone, B alone, C alone, A and B together, A and C together, B and C together,
and/or A, B, and C together, etc.). In those instances where a convention analogous to
“at least one of A, B, or C, etc.” is used, in general such a construction is intended in
the sense one having skill in the art would understand the convention (e.g., “a system
having at least one of A, B, or C” would include but not be limited to systems that
have A alone, B alone, C alone, A and B together, A and C together, B and C together,
and/or A, B, and C together, etc.). It will be further understood by those within the art

that virtually any disjunctive word and/or phrase presenting two or more alternative
terms, whether in the description, claims, or drawings, should be understood to
contemplate the possibilities of including one of the terms, either of the terms, or both
terms. For example, the phrase “A or B” will be understood to include the possibilities
of “A” or “B” or “A and B.”
[0044] It will be further appreciated that functions or structures of a plurality of
components or steps may be combined into a single component or step, or the
functions or structures of one-step or component may be split among plural steps or
components. The present invention contemplates all of these combinations. Unless
stated otherwise, dimensions and geometries of the various structures depicted herein
are not intended to be restrictive of the invention, and other dimensions or geometries
are possible. In addition, while a feature of the present invention may have been
described in the context of only one of the illustrated embodiments, such feature may
be combined with one or more other features of other embodiments, for any given
application. It will also be appreciated from the above that the fabrication of the unique
structures herein and the operation thereof also constitute methods in accordance with
the present invention. The present invention also encompasses intermediate and end
products resulting from the practice of the methods herein. The use of “comprising”
or “including” also contemplates embodiments that “consist essentially of” or “consist
of” the recited feature.
[0045] Although embodiments for the present subject matter have been described in
language specific to structural features, it is to be understood that the present subject
matter is not necessarily limited to the specific features described. Rather, the specific
features and methods are disclosed as embodiments for the present subject matter.
Numerous modifications and adaptations of the system/component of the present
invention will be apparent to those skilled in the art, and thus it is intended by the

appended claims to cover all such modifications and adaptations which fall within the
scope of the present subject matter.

WE CLAIM:
1. A method for welding a three-piece safety valve for ultra-super critical boiler
application, the method comprising the steps of:
preparing a furnace system comprising of at least one dissimilar metal having
different compositions and different welding temperature;
welding the at least one dissimilar metal using a welding electrode;
buttering and inter-passing the three dissimilar metals to achieve a desired
thickness,
heating the three dissimilar metals post to the buttering with the inter-pass
temperature maintained at a specified set level;
cooling the three dissimilar metal weld; and
forming a base (1), a seat bushing (2), an inlet neck (3) and a joining weld (4)
for the three-piece safety valve.
2. The method as claimed in claim 1, wherein the cooling the three dissimilar
metal weld is followed by radiographic testing the finished weld to verify the
soundness.
3. The method as claimed in claim 1, wherein the welding at least one dissimilar
metal is carried out by exposing to a shielded metal arc welding and sequential
welding with heat treatment cycle for obtaining defect free weld.
4. The method as claimed in claim 1, wherein the inter-pass temperature
maintained is 980°C, the seat bushing (3) undergo post weld heat treatment
(PWHT) at 980±10°C after weld buttering and post full welding, the joint of
all three pieces together undergo PWHT at 760±10°C.
5. The method as claimed in claim 1, wherein the three-piece safety valve is
designed to withstand high pressure and high temperature up to 620oC.

6. The method as claimed in claim 1, wherein the at least one dissimilar metal is
selected from a group including Grade 92 steel, Inconel Alloy 617 and stainless
steel CF8M material.
7. The method as claimed in claim 1 or 5, wherein the base (1) is made up material
including CF8M stainless steel material, the seat bushing (2) is made up of
material including Inconel Alloy 617, and the inlet neck (3) is made up of
material including Grade 92 steel.
8. The method as claimed in claim 1, wherein the three-piece safety valve
welding is performed using weld buttering and butt welding which further uses
shielded metal arc welding (SMAW) process, and welding parameters are the
electrode size for weld buttering includes 3.15 mm diameter, butt welding
electrode size includes 2.5 mm diameter, 3.15 mm diameter, 4.0 mm diameter,
preheat temperature of butt welding is approximately 220o C, the current used
for weld buttering is approximately 109 Amps, current used for butt welding
is in the range of 75 -143 Amps, voltage for weld buttering is of 21V, voltage
for butt welding is in the range of 20-25V, Interpass temperature for weld
buttering is approximately <150ᵒC and Interpass temperature for butt welding
is approximately <350ᵒC, travel speed for weld buttering is about 91
mm/minute, travel speed for butt welding is in the range 70-130 mm/minute,
bead type for weld buttering is stringer type and bead type for butt welding is
stringer & weave type.
9. The method as claimed in claim 1, wherein the at least one dissimilar material
grooves are edge prepared and butt welding is performed between the base
(1), the seat bushing (2) and the inlet neck (3) using the welding electrode
and a stainless steel wire-brush and acetone are used to remove inter-pass
oxides formed during the welding.

10. The method as claimed in claim 1, wherein the three-piece safety valve is used
in power plant erection application, commissioning areas and shop floor
manufacturing areas.