FIELD OF THE INVENTION
The present invention relates to elimination of multiple post weld heat
treatment and distortion control in Economizer intermediate headers of
high pressure boilers. More particularly, this invention presents a
method for designing of economizer intermediate headers with alternate
materials to avoid multiple post weld heat treatment (PWHT) while
complying with the statutory requirements for the header boiler
operating conditions.
BACKGROUND OF THE INVENTION
The Header in a super critical boiler is a junction in which water or
steam or mixture of water and steam is collected at one side and
distributed at other side. Normally Reducers, Elbows, TEEs and tubes
are welded on the header to connect with different parts in the boiler as
inlet and outer points. The four Numbers of Economizer intermediate
headers of high pressure boilers such as 800 MW super critical boilers
are made with two rows of multiple nipples. Each row is having different
material thickness and different size and specification. Header pipe is
made up of D273 X 60 - SA335P12 – a high pressure steel pipe (Item No.
1 in Figure 1) material, one row is TD 69.85 X 15.09 - SA213T22- an
alloy tube (Item No. 2 in Figure 1) and another row is built with TD 50.8
X 9.14 - SA210GrC- an alloy tube (Item No. 3 in Figure 1). Normally alloy
steel headers will be post weld heat treated in a batch furnace after
completing all welding as per drawing to relieve thermal stresses formed
due to welding. The range of temperature in which post weld heat
treatment to be conducted as per Indian Boiler Regulation is presented in
Table-1. For the combinations of materials, the post welding heat
treatment (PWHT) may be selected as per ASME (American Society of
Mechanical Engineers (ASME) standard that regulates the design and

construction of boilers and pressure vessels). The stress relieving
temperature for the above material combination is 695 +/-15 Deg C
(Refer Table-2) since thickness of SA213T22 (02) tube is 15.09 mm. But,
the SA210GrC material along with the header should not be subjected to
this higher temperature. Otherwise, the tensile strength of carbon steel
will decrease due to exposure in this high temperature range. So, the
process sequence for this combination is, firstly the SA213T22 tubes (02)
of 109 Nos. should be welded and heat treated in furnace at 695 +/-15
Deg C and after that SA210GRC tubes of 190 Nos. to be welded followed
by stress relieving at 655 +/-15 Deg C.
In other words, the existing headers were built by SA335P12 pipe (01)
with SA213T22 (02) and SA210GrC (03) tubes on it. This combination
requires stress relieving at 695+/-15 Deg C. But, SA210GrC material
should not undergo this temperature otherwise it will lose its tensile
strength. The process sequence is to weld 109 Nos. of SA213T22 nipples
and carrying out stress relieving at 695+/-15 Deg C and further welding
190 Nos. of SA210GRC following by 655+/-15 Deg C stress relieving
cycle. This will cause more distortion and increase cycle time
substantially.
Figure 3 explains the conventional process flow of said headers. The
aforesaid multiple post weld heat treatment (PWHT) in a header causes
distortion in the header and increases product manufacturing cycle time.


Hence, in light of the foregoing a person skilled in the art would
appreciate that there remains a need for designing of economizer
intermediate headers with alternate materials to avoid multiple post weld
heat treatment (PWHT) while complying with the statutory requirements
for the header boiler operating conditions.
OBJECTS OF THE INVENTION
An object of the invention is to overcome the aforementioned and other
drawbacks existing in prior art systems and methods.
More particularly, it is an object of the invention to design economizer
intermediate headers with tubes of suitable material combinations to
avoid multiple post weld heat treatment (PWHT) cycles.

Still another object of the invention is to design economizer intermediate
headers with tubes of suitable material combinations to avoid multiple
straightening activities.
Yet another object of the invention is to design economizer intermediate
headers with tubes of suitable material combinations to prevent
changing the properties of the medium flowing inside the economizer
intermediate headers used in economizer zone of boilers.
These and other objects and advantages of the present invention will be
apparent to those skilled in the art after a consideration of the following
detailed description taken in conjunction with the accompanying
drawings in which a preferred form of the present invention is illustrated.
SUMMARY OF THE INVENTION:
Then present application discloses a method for designing an economizer
intermediate header section of a high pressure boiler for reducing
multiple post weld heat treatment and straightening cycles. Further, the
method includes welding of a pipe (01) made of a first combination of
materials to a header. Further, the method, in an aspect, includes
welding of a first tube (02) made of a second combination of materials to
a first row. In another aspect, the method further includes welding of a
second tube (04) made of a third combination of materials to a second
row followed by a post welding heat treatment of the header.
In a preferred embodiment, the third combination of materials contains
carbon (C) in the range of 0.05-0.015 %, Manganese (Mn) in the range of
0.30-0.61%, Phosphorus (P) not greater than 0.025, Sulphur (S) not

greater than 0.025, Silicon (Si) not greater than 0.50, chromium (Cr) in
the range of 0.80-1.25%, Molybedenum (Mo) in the range of 0.44-0.65%.
The above and additional advantages of the present invention will
become apparent to those skilled in the art from a reading of the
following detailed description when taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The drawings refer to embodiments of the invention in which:
Figure 1 illustrates the conventional configuration of a header.
Figure 2 illustrates the modified configuration of a header according to
an embodiment of the present invention.
Figure 3 illustrates the conventional process flow chart before
modification.
Figure 4 shows the process flow chart after modification according to an
embodiment of the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Although the disclosure hereof is detailed and exact to enable those
skilled in the art to practice the invention, the physical embodiments
herein disclosed merely exemplify the invention which may be embodied
in other specific structure. While the preferred embodiment has been

described, the details may be changed without departing from the
invention, which is defined by the claims.
It will be apparent, however, to one of ordinary skill in the art that the
present invention may be practiced without specific details of the well
known components and techniques. In other instances, well known
techniques or methods have not been described in detail but rather in
Figures in order to avoid unnecessarily obscuring the present invention.
Further specific numeric references should not be interpreted as a literal
sequential order. Thus, the specific details set forth are merely
exemplary. The specific details may be varied from and still be
contemplated to be within the scope of the present invention. The
features discussed in an embodiment may be implemented in another
embodiment.
Moreover occasional references to the conventional header
configuration/design are made in order to better distinguish the present
inventive disclosure discussed later in greater detail. Few of the details
pertaining to the materials making the tubes/nipples positioned on the
header are well-known in the art, and therefore, are described herein
only in the detail required to fully disclose the present invention.
Improving upon the conventional techniques discussed at length above
(background), in the present disclosure the clearly makes the
configuration of the header of the high pressure boilers as disclosed in
the present application advantageous over the existing arts as would also
become clearer to the knowledgeable in the art with the particulars of the
aforesaid techniques being described below in greater detail.

Turning to Figure 2, the material of Item no. 04 altered from initial
SA210GRC to SA213T12. This combination of pressure parts can
undergo single final post weld heat treatment at 695+/-15 Deg
centigrade instead of two post weld heat treatments at two different
temperature cycles.
Figure 4, shows the manufacturing process chart of economizer
intermediate header after inventively identifying the combination of
materials and thereby configuring the header with suitable tubes. Two
stages of post weld heat treatment and straightening in press for
distortion control eliminated and the final post weld heat treatment alone
carried out after welding all nipples/tubes (02,04)) on header pipe. It is
noted herein that the Tubes and Nipples are one and the same and are
used interchangeably. In a header, multiple tubes are welded radially on
the pipe which is disposed on the rows to distribute the medium to
another system. This reduces distortion during stress relieving in batch
furnace and consequent hot correction to rectify it. With this
improvement 84 production hours are saved. Thereby, eliminating the
drawbacks in the background as aforesaid mentioned.
Further, elaborating the basis and limitations of designing economizer
intermediate headers, it is mentioned herein that post analyzing
analysing the combination of nipple materials on headers, the SA213T22
material cannot be changed due to load requirements from connecting
hanger tubes. Herein, tubes in boilers are generally used for heat and
mass transfer whereas hanger tubes are used to carry load along with
Heat and mass transfer. In other words, the hanging load of Economizer
Intermediate headers and economizer coils may be borne by the Hanger
tubes. Thus, in a preferred embodiment since the SA213T22 material

cannot be changed due to load requirements from connecting hanger
tubes, SA210GrC tubes (03) have been changed to SA213T12 tubes (04)
of same size which will not change the properties of medium flowing
inside the header. This higher grade material also meets the design
requirements of this header in the boiler. The earlier design warrants
SA213T22 nipple welding with one PWHT followed by Straightening in
press for distortion control and further welding of SA210GrC tubes (03)
with another PWHT followed by straightening in press for distortion
control. This change in header nipple warrants only single final post weld
heat treatment after completing all welding on header pipe followed by
single straightening in press. The chemical composition of major
elements in SA213T12 material as per standard is presented below
which satisfies the code requirement for header also. In a preferred
embodiment, the higher Chromium and Molybdenum content in
SA213T12 compared to SA210GrC allows heat treatment at 695 +/- 15
degree centigrade which reduces one heat treatment cycle, in one aspect.
Hence, the need for multiple post weld heat treatment and straightening
activities are removed.
The below table shows the content of the constituent materials in
SA213T12:

Advantages
In a typical 800 MW super critical type boiler which is a type of a high
pressure boiler, four numbers of economizer intermediate headers were
having material combination that warrants multiple post weld heat

treatment. Changing tube material from SA210GRC to SA213T12 needs
only one post weld heat treatment and straightening activity. The details
of the modifications are produced as below.

The foregoing is considered as illustrative only of the principles of the
invention. Furthermore, since numerous modifications and changes will
readily occur to those skilled in the art, it is not desired to limit the
invention to the exact modification and process as described. While the
preferred embodiment has been described, the details may be changed
without departing from the invention, which is defined by the claims.

We Claim:
1. A method for designing an economizer intermediate header section of a high
pressure boiler for reducing multiple post weld heat treatment and straightening
cycles, the method comprising:
welding of a pipe (01) made of a first combination of materials to a
header;
welding of a first tube (02) made of a second combination of materials to
a first row;
welding of a second tube (04) made of a third combination of materials to
a second row;
post welding heat treatment of the header.
2. The method as claimed in claim 1, wherein the first row and the second row are
positioned on the header.
3. The method as claimed in claim 1, wherein the third combination of materials
comprises carbon (C) in the range of 0.05-0.015 %, Manganese (Mn) in the
range of 0.30-0.61%, Phosphorus (P) not greater than 0.025, Sulphur (S) not
greater than 0.025, Silicon (Si) not greater than 0.50, chromium (Cr) in the
range of 0.80-1.25%, Molybedenum (Mo) in the range of 0.44-0.65%.
4. The method as claimed in claim 1, wherein the high pressure boiler is an 800
MW super critical type boiler.
5. The method as claimed in claim 1, wherein the post welding heat treatment of
the header occurs in the range of 680-710 degree centigrade.
6. The method as claimed in claim 1, wherein the welding is of a butt welding type.