Claims:1. Method of local PWHT of weld joints in boiler membrane water wall panels, wherein the weld joints include tube to tube butt welds (3), tube to filler fin fillet welds (5) and filler fins (4) to preexisting fins butt welds (5a), the method comprising steps of:-
- positioning one resistance heating element (7) on one half of tube (1) present in one side of the panel that the center of length of the resistance heating element (7) lies at the tube to tube butt weld (3) present in that tube (1) and another resistance heating element (7a) on the other half of the tube (1) present in other side of the panel that the center of length of the resistance heating element (7a) lies at the same tube to tube butt weld (3) present in the tube;
- identification of two locations one each for fixing feedback thermocouples (10) for heating the resistance heating element (7, 7a) that are positioned one each on both the sides of the membrane wall panel that the one resistance heating element (7) is placed on 12 o clock position of the tube to tube butt weld (3) and its corresponding feedback location (6) fixed at the 10 o clock position of the tube to tube butt weld (3) and another resistance heating element (7a) is placed on 6 o clock position of the tube to tube butt weld (3) and its corresponding feedback location (6a) is fixed at the 5 o clock position of the tube to tube butt weld (3).

2. The method of local PWHT of weld joints in boiler membrane water wall panels as claimed in claim 1, wherein the feedback thermocouples (10) are connected to the resistance heating power source (11) for closed loop heating of the panel, wherein the power source (11) comprises of multiple heating channels with each heating channel in connection to one said resistance heating
element and one thermocouple (10) which is fixed in the feedback location corresponding to the heating pad.

3. The method of local PWHT of weld joints in boiler membrane water wall panels as claimed in the claim 1 or 2, wherein said each heating channel of the power source (11) powers one resistance heating element using the respective feedback temperatures sensed from the thermocouples (10) placed in the locations and two resistance heating element (7, 7a) are placed on a single tube to tube weld (3) with each said resistance heating element heating one half of the tube to tube butt weld (3) and the adjoining fin welds ((5) and (5a)).

4. The method of local PWHT of weld joints in boiler membrane water wall panels as claimed in the claims 1-3, wherein the heating elements (7) and (7a) are connected to the resistance heating power source (11) through the power cables (8) and additional thermocouples (9) are taken from the location (6) and are connected to the temperature recorder (12) that records the PWHT temperature versus time in a chart paper.

5. The method of local PWHT of weld joints in boiler membrane water wall panels as claimed in the claims 1-4, wherein the resistance heating element (7) that is placed on one side of the panel is connected to one such heating channel of the power source (11) using the power cables (8) and the feedback for this channel is provided by the feedback thermocouple (10) that is placed in the location (6).

6. The method of local PWHT of weld joints in boiler membrane water wall panels as claimed in the claims 1-5, wherein the FCP (7a) that is placed on the other side of the panel is connected to another heating channel of the power source (11) using the power cables (8) and the feedback for this channel is provided by the feedback thermocouple (10) that is placed in the location (6a).

7. The method of local PWHT of weld joints in boiler membrane water wall panels as claimed in the claims 1-6, wherein the heat treatment is performed using the power source (11) for achieving the desired soaking temperature by proceeding at a heating ramp not exceeding 200°C/hour.

8. The method of local PWHT of weld joints in boiler membrane water wall panels as claimed in the claims 1-7, wherein the tubes and fins of the boiler water walls are normally of dissimilar thicknesses.

9. The method of local PWHT of weld joints in boiler membrane water wall panels as claimed in the claims 1-8, wherein the membrane water walls panels can be made of CSEF steels, that are the class of steels whose microstructures are precisely controlled by careful alloy additions and resulting in significantly high creep strength compared to normal alloys steels. , Description:FIELD OF THE INVENTION
[001] The present invention relates to a method of carrying out local Post-weld heat treatment (referred to as PWHT hereinafter) of the weld joints made in membrane water wall panels intended for use in power boilers, by using flexible ceramic resistance heating pads.
BACKGROUND/PRIOR ART OF THE INVENTION
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[003] Fossil fuel fired boilers are widely used for thermal power generation wherein the conventional fossil fuel is burnt and the heat of combustion is used to convert water into steam which then turns the turbine leading to generation of electricity. Boilers are composed of membrane water walls which are structures composed of tubes and fins welded alternately. The heat of combustion of the burnt fuel is absorbed by the water that flows within such water wall panels by way of the heat transfer that happens across the walls of the tubes present in the water walls.
[004] The water walls are fabricated by joining several tubular panels of smaller lengths so as to make long walls of desired dimensions. The joining of the panels is made by welding. The tubes of the mating panels are joined as butt weld and the fins surrounding the butt welds are attached to the adjacent tubes by way of fillet welds. The material of composition of the water walls are chosen in such a way as to endure
long operation under exposure of high temperature and pressure. When such high temperature resistant materials are welded, it more often than not calls for a proper PWHT to temper the weld metal and to relax the residual stresses formed during welding. The PWHT is an important operation which when not done properly, is likely to result in weld failures either during initialization of the boiler like during hydro test or light-up or during subsequent operation as well.
[005] The problem is more pronounced in the case of boiler erection sites where the uncertainties with regard to post weld heat treatment are quite high as this is performed locally covering only the joint area and some portions of the base metal. Therefore, a proper method of local PWHT along with a suitable technique is highly essential for imparting a proper PWHT for weld joints of membrane water walls which would ensure a proper PWHT effect of the welds concerned and would thereby eliminate the risk of any operational failure later.
[006] Now, reference may be made to the following prior arts.
[007] US patent 6676777 B2 describes a post weld heat treatment process, wherein a welded joint made of carbon steel and low alloy steel is held within austenite single-phase temperature range for a given time and subsequently the joint is cooled by air-cooling or by slow cooling at a cooling rate lower than that of the air-cooling. Whereas our invention describes a technique of local PWHT applicable for membrane water wall panels of boilers that takes care of heat treatment of both the tube to tube butt weld and the tube to fin fillet welds in the same PWHT cycle, using flexible ceramic resistance heating pads.
[008] 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 a technique of carrying out most effective local PWHT for membrane water wall panels of boilers in which the PWHT of both the tube to tube butt welds and tube to fin fillet welds are carried out in the same PWHT cycle, using flexible ceramic resistance heating pads.
[009] Chinese Patent CN 102796863 A relates to a method of a local post weld heat treatment of a steel casting, and particularly relates to a method used for a local post weld heat treatment of a large-size steel casting after re-welding. The method comprises the following steps of: firstly, carrying out hardness detection on a welding zone after re-welding, wherein the hardness does not exceed a critical upper cutoff hardness and thereafter conducting an induction heat treatment for better quality of cast products. Whereas, our invention relates to a novel technique for carrying out local PWHT of membrane water wall panels comprising of tube to tube butt welds and tube to fin fillet welds wherein the former and latter are heat treated in a single PWHT cycle, using flexible ceramic resistance heating pads.
[010] European patent EP 0034057 B1 discusses a method for post weld heat treatment of a welded portion of, for example, a thick base metal, and more particularly to a method for appropriately judging the time point for terminating the PWHT when sufficient of the residual diffusible hydrogen in the welded metal has been dissipated by the after heating. But, our invention relates to a technique of carrying out local PWHT (using flexible ceramic resistance heating pads) of both tube to tube butt welds and tube to fin fillet welds made in membrane water wall panels of thermal power boilers.
[011] None of the above can fulfill the requirements of the present invention, for which it is designed. Hence, the present invention has been introduced.
OBJECTS OF THE INVENTION
[012] It is an object of the present disclosure to propose method of local post weld heat treatment of weld joints in boiler membrane water wall panels which overcomes disadvantages of prior art.
[013] An object of the invention is to propose method of local post weld heat treatment of weld joints in boiler membrane water wall panels wherein the tube to tube butt welds and tube to fin fillet welds are heat treated in a single PWHT cycle using flexible ceramic resistance heating pads, instead of performing two separate PWHT cycles one for the tube to tube welds and one for the tube to fin fillet welds.
[014] Another object of the invention is to propose method of local post weld heat treatment of weld joints in boiler membrane water wall panels which results in potential savings in cycle time of heat treatment.
[015] Still another object of the present invention is to provide method of local post weld heat treatment of weld joints in boiler membrane water wall panels which reduces the possibility of local warping of the panels, by a great extent, when such PWHT is performed.
[016] 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
[017] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.
[018] In the present invention, there is provided a most effective technique of PWHT of weld joints made in membrane water wall panels of boilers with the special feature being PWHT of tube to tube joints and tube to fin joints being heat treated in the same PWHT cycle, thereby reducing the cycle time of PWHT operation in fabrication of such boiler membrane walls. The novelty of this invention lies in the fact that the tubes and fins used in the construction of the boiler water walls are normally of dissimilar thicknesses. So, PWHT of the tube to tube butt weld and tube to fin fillet weld need to be carried out separately in order to achieve a soaking temperature within a tolerance band of 15° C in a PWHT cycle.
[019] According to the invention, a technique for carrying out post weld heat treatment of welds made in membrane water wall panels of boilers, is disclosed. The invented technique is capable of heat treating both the tube to tube butt welds and the tube to fin fillet welds (which are of unequal weld thickness) in a single PWHT cycle, resulting in the advantage of elimination of a situation wherein the former and the latter welds are heat treated separately in two PWHT cycles thereby also resulting in reduction of heat treatment cycle time.
[020] The membrane water wall panels comprise of tubes welded with fins positioned alternately i.e. a tube-fin-tube-fin etc. kind of an arrangement. The length and width of the panels are as per the design of the boiler. Tubes are fillet welded with fins. Weld joints have to be made to achieve the required length of the membrane water wall panels at different locations and at different elevations in a boiler. Two types of weld joints are seen when such panels are joined at site to form larger panel assemblies namely the tube to tube butt welds and tube to fin fillet welds.
[021] PWHT has to be carried out for the tubular butt welds, the fillet welds made in the membrane water wall panels and also for the butt welds, that are made between the fins that are positioned after welding of tube butt welds, and the preexisting fins of the panels joined by welding. The proposed technique involves carrying out the PWHT of both the tube to tube butt welds and the tube to fin fillet welds in a single PWHT as opposed to the widely prevalent practice of doing the PWHT in two separate PWHT cycles. The reason behind the conventional method of performing PWHT separately for tube and fin welds is that both these members have different thickness and generally it is not possible to heat treat members of different thicknesses in a single cycle especially when the heat treatment tolerance is very tight. This is because when the feedback thermocouple for sensing the temperature during heat treatment is taken from the tube weld, then the fin portions are likely to get overheated and if feedback is taken from fins, then the tubes may not be adequately heated. But, the proposed procedure ensures that the PWHT of both tube welds and fin welds are performed in the same cycle within a tolerance band of 15° C i.e. the maximum and minimum temperatures seen during the PWHT is within a range of 15° C (maximum). This has been made possible because of two reasons.
a) Using a special type of resistance heating element in the form of flexible ceramic pad (FCP) called as CP48, which is a long pad with a high length to width ratio, wherein the heating is carried out so as to distribute the heat uniformly across the tube welds and the fin welds.
b) The feedback thermocouple is positioned in the point where the tube to tube butt weld meets the adjacent fin weld. It is this junction point which when used as spot for providing feedback of temperature during PWHT, ensures a uniform rise of temperature both in tube and the fin welds.
c) Proceeding at a rate of heating not greater than 200° C per hour, during the PWHT process, in order to keep the tendency of warping of panels under control.

[022] These three novel features are not disclosed in any of the prior arts. In addition to these novel features, the proposed PWHT procedure results in dual benefit of cycle time savings since all the tube to tube butt welds, tube to fin welds and fin to fin welds are heat treated in a single PWHT cycle and possibility of reduction of local warpage of the heat treated panels on account of the control heat addition of the panel.
[023] The PWHT procedure is described hereinafter briefly. Two numbers of the CP48 flexible ceramic pad (FCP) for each tube to tube butt weld is placed on the tube butt welds in such a way that the tube butt weld line lies in the center of the length of the CP48 pad. One CP48 FCP is placed on the 12 o clock position of the tube butt weld and the other pad is placed diametrically opposite to the first pad i.e. on the 6 o clock position of the tube butt weld. Then, for the first CP48 pad, the feedback thermocouple is spot welded in the junction point where the tube to tube butt weld meets the adjacent fin fillet weld on the one side say to the right side of the pad (which is close to 5 o clock position of the tube butt weld above which the pad is laid). Similarly, on the other side of the panel, the feedback thermocouple is spot welded on the location where the tube to tube butt weld meets the fillet weld of the fin that is placed adjacently to the left of the tube (i.e. close to the 10 o clock position of the tube butt weld above which the pad is laid).
[024] After placement of the FCP and the feedback thermocouples, the area to be heat treated, is closed with the ceramic wool insulation material. Then, PWHT is performed using a power source which can perform PWHT in the auto control mode using the temperature feedback sensed from the feedback thermocouples that were fixed earlier. Since two numbers are placed on each tube butt weld, one on the top side and another on the bottom side, these two pads are connected to two separate heating channel of the power source with the temperature feedback being taken (for heating them) from the respective spots as mentioned earlier. Then, the PWHT cycle is run using the required heating rate, soaking time and the required cooling rate as per the relevant material specifications or code of manufacture like ASME BPVC or IBR etc.
[025] This procedure ensures uniform heating in both the tube and fin welds in the same PWHT cycle within a maximum temperature difference of 15° C during the soaking period of the PWHT cycle. The said procedure is applicable for welds made in boiler water walls made of a variety of grades of steel.
[026] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
[027] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[028] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[029] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein: -
Figure 1 – Schematic sketch of a typical boiler membrane water wall panel with cross sectional view in the bottom.
Figure 2 – Schematic sketch of two panels being welded wherein there are butt welds made between faying tubes and the adjoining fin portions are removed for facilitating the butt welding of tubes when joining one membrane water wall panel to another.
Figure 3 - Schematic sketch of two panels being welded wherein after completing tube butt welds, filler fins are placed in the areas where fins were removed earlier and the fin to tube fillet welds and the fin to fin welds are completed.
Figure 4 – Sketch of Flexible Ceramic Pad (FCP).
Figure 5 – Schematic sketch of the PWHT set-up comprising of power source, feedback thermocouples, FCP heating element and temperature recorder, for heat treatment of tube to tube butt welds and tube to fin fillet welds in a single PWHT cycle according to present invention.
Figure 6 – Illustrative sketch depicting the locations from where the temperature feedback is taken for heating the panel (one location is on one side of the panel and the other is on the rear side of the panel) in accordance with present invention.
[030] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily 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 THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS OF PREFERRED EMBODIMENTS
[031] 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.
[032] The present invention makes a disclosure regarding a technique for carrying out post weld heat treatment (PWHT) of welds made in membrane water wall panels of boilers in general and for membrane water walls panels made of CSEF steels, in particular. The CSEF steel are the class of steels whose microstructures are precisely controlled by careful alloy additions and resulting in significantly high creep strength compared to normal alloy steels.
[033] Now, reference may be made to the accompanying figures.
[034] The membrane water wall panels are the structures used in thermal power boilers that are composed of alternately placed tubes (1) and fins (2) which are welded to one another as shown in figure 1. The tubes (1) and fins (2) are welded using fillet welds as seen in the cross sectional view of the membrane water wall panel shown in the bottom of figure 1. The tube size, fin size and the length and width of the membrane water wall panels are decided as per the design of the boiler. The membrane water wall panels are first fabricated to transportable sizes in the shop floors and later these units have to be welded at power plant erection sites. When welding one membrane wall panel with another, the fins contiguous to the tube ends of both the matching panels are removed up to a minimum width of around 30 mm in each of the panel, in order to facilitate the tube to tube butt welding of the faying ends of the matching panels. The figure 2 shows the way in which two membrane wall panels are joined by welding. The portion of fins adjoining the tube butt joints are found removed and the tube weld joints (3) are seen in figure 2. After completion of the tube to tube butt weld, filler fins (4) are placed in the portions where fins were removed earlier and the weld is made between the filler fins and the adjoining tubes by way of fillet welds (5) and the filler fins are joined with already existing fins by way of butt welds (5a). The figure 3 illustrates a sample case depicting the situation of two membrane wall panels welded where filler fins (4) are shown cross hatched and there are filler fins (4) to tube fillet welds (5) and there are butt welds (5a) connecting filler fins (4) with the preexisting fins.
[035] After joining two membrane panels by way of welds (3), (5) and (5a) i.e. by way of tube to tube butt welds, filler fins to tube fillet welds and butt welds made between filler fin to preexisting fins, the welds thus made are required to be post weld heat treated (PWHT) in order to sufficiently temper the microstructure of the welds and to relieve the welds of the residual stresses generated during welding. In the absence of a proper PWHT, there is a probability of failure of tube welds to happen either during the hydro test of boiler or during subsequent operation. The membrane water wall panels made of the CSEF steels, in particular, are highly prone to many environment-assisted cracking issues, especially when the welding or the subsequent PWHT is not carried out properly. Therefore, the weld joints in such panels require a proper PWHT technique that is effective enough to temper the weldment and the HAZ and result in restoration of good ductility and toughness to the material thereby avoiding the occurrence of any environment assisted cracking issues. This technique is disclosed in detail in the present invention.
[036] As depicted in figures 2 & 3, the panel to panel weld joints are composed of tube to tube butt welds (3), tube to filler fin fillet welds (5) and filler fins (4) to preexisting fins butt welds (5a) of the panels. All these welds require heat treatment to be done with proper spread of heat across all these areas. It was studied and established by the authors of this proposed invention after several experiments, that the following procedure heat treats all the above mentioned welds namely (3), (5) and (5a) in a most effective manner and within a narrow tolerance range of 15° C in the soaking temperature during the soaking stage of the heat treatment.
[037] The success of the heat treatment lies in identifying the correct spot or location for the placement of the feedback thermocouple which is taken as reference temperature for the power source to heat the resistance heating element. The general arrangement of the PWHT set-up of the panel to panel joints is shown in figure 5.
(1) There is a special type of FCP (resistance heating element) called as CP48 (7) which is a long strip type of heater spanning over a length of 1200 mm approximately as best seen in figure 4. This CP48 heating element (7) is placed on the tube to tube butt weld, in such a way that the centre of length of the CP48 pad (7) is present on tube to tube butt weld (3) that is required to be heat treated. One CP48 pad (7) is placed on one side of the panel and another similar pad (7a) is placed on the other side of the panel as illustrated in figure 6. This means that two CP6 pads namely (7) and (7a) (as seen in figure 6) together heat one tube comprising the tube to tube butt weld (3).
(2) Next, the feedback thermocouples (10) are fixed by means of capacitor discharge welding process, in the locations (6) and (6a) (as shown in figures 5 and 6 respectively), where the tube to tube butt weld meets the tube to filler fin fillet weld (5). The locations (6) and (6a) where the feedback thermocouples (10) originates are illustratively shown in figure 6. It can be seen from figure (6) that the both the CP48 heating pads are placed in the 12 o clock and 6 o clock position of the tube, while the locations (6a) and (6) of feedback thermocouples are respectively fixed at 5 o clock position and 10 o clock position.
(3) Such a placement of feedback thermocouples (10) at locations (6) and (6a) results in uniform heating of both the tube and fin simultaneously at the same rate of heating. The feedback thermocouples (10) are connected to the resistance heating power source (11) for closed loop heating of the panel.
(4) Then, the heating elements (7) and (7a) are connected to the resistance heating power source (11) through the power cables (8) and additional thermocouples (9) are taken from the location (6) and are connected to the temperature recorder (12) that records the PWHT temperature versus time in a chart paper.
(5) The power source (11) working on closed loop feedback control system comprising of options for programming the entire PWHT cycle including the rate of heating, soaking temperature, soaking time and the rate of cooling. The power source also comprises of multiple heating channels wherein each heating channel powers one FCP.
(6) The Resistance Heating Element (7) that is placed on one side of the panel is connected to one such heating channel of the power source (11) using the power cables (8) and the feedback for this channel is provided by the feedback thermocouple (10) is placed in the location (6). The FCP (7a) that is placed on the other side of the panel is connected to another heating channel of the power source (11) using the power cables (8) and the feedback for this channel is provided by the feedback thermocouple (10) that is placed in the location (6a).
(7) With reference to figure (6), the feedback thermocouple for the CP48 pad (7) placed on the top side of the panel is taken from the location (6) whereas the feedback thermocouple for the CP48 pad (7a) placed on the other side of the panel is taken from the location (6a).
(8) Then, each heating pad and its corresponding feedback thermocouple taken from the location as mentioned in the point (7) above (i.e. at the point of intersection of the tube to tube butt weld with the tube to filler fin fillet weld) are connected to one heating channel of the power source (11). For instance, FCP (7) and its corresponding feedback thermocouple taken from location (6) (as seen in figure 6) are connected to one heating channel of the power source (11). Further, since two heating pads are required to heat one tube and its associated welds, two heating channels will be required for heating one tube and its associated welds. Therefore, if ‘N’ heating channels are available in the power source, then (N/2) numbers of tubes and their associated welds can be heat treated.
(9) Similarly, all the FCP pads are connected along with their respective thermocouples and heat treatment of as many numbers of the three types of welds ((3), (5) and (5a)) as possible based on the setting described in point (8) above is performed using the power source (11) in the auto control mode with the feedback control system.
(10) The heat treatment is then performed using the power source (11) for achieving the desired soaking temperature, by proceeding at a heating ramp not exceeding 200° C/hour. Since, the power source (11) consists of multiple channels, multiple numbers of tube to tube welds and the two types of accompanying welds can be heat treated in a single PWHT cycle.

[038] The above mentioned heat treatment technique is ideally suited for heat treatments of welds made for joining one membrane wall panel to another such panel, for the purpose of building the membrane water walls of thermal power boiler applications. The technique is ideally suited for heat treatments of welds made for joining membrane wall panels made of Creep-strength enhanced ferritic (CSEF) steels. The use of the above procedure results in a maximum temperature variation sensed among any of the welds that are heat treated in a single cycle of PWHT, within 15° C always.
[039] The major advantages of the present PWHT procedure is listed hereinbelow:-
(1) All the three types of welds namely tube to tube butt welds (3), tube to filler fin fillet welds (5) and butt welds made between filler fins and the pre-exisiting fins of the panels in one PWHT cycle thereby avoiding the heat treatment in three stages wherein all the three welds are heat treated separately. Thus, this results in cycle time savings in heat treatment of panel to panel welds.
(2) The usage of CP48 strip type of FCP and the combination of a rate of heating lower than 200° C / hour, ensures uniform spread of heat just sufficient to heat treat all the three types of above mentioned welds and results in no significant local warpage of panel in the heat treated areas.

[040] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[041] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.
[042] 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 particulars 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”.
[043] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.
[044] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[045] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[046] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.