Description:“IMPROVED HW-GTAW PROCESS FOR PRODUCING DISSIMILAR MATERIAL TUBE BUTT JOINTS OF SUPER ALLOY 617 AND 740H”

FIELD OF THE INVENTION:

[001] The invention generally relates to mechanized Hot Wire GTAW technique for dissimilar weld joints of nickel based solid solution strengthened alloy (UNS N06617) and nickel based age hardening strengthened alloy (UNS N07740) to produce boiler components. More particularly, the invention relates to an improved HW-GTAW process for producing dissimilar material tube butt joints of solid solution strengthened Nickel based super alloy 617 and precipitation hardened nickel based super alloy 740.

BACKGROUND OF THE INVENTION/PRIOR ART:

[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] HW-GTAW process for producing dissimilar weld joints are not known in the art, in particular dissimilar butt welding of alloy 617 and alloy 740H using fully mechanized HW-GTAW procedure. However, technology related to HW-GTAW process disclosed in the art may include:

[004] Patent No. EP 0194045 B1, Filing Date: February 10, 1986, Publication date January 31, 1990.
[005] This invention relates to TIG (Tungsten Inert Gas) welding equipment, and more particularly to welding equipment suitable for performing semi-automatic hot wire TIG arc welding. In this investigation the applicant (Babcock – Hitachi Kabushiki Kaisha) claims that a semi-automatic hot wire TIG (Tungsten Inert Gas) welding equipment comprising: a portable TIG arc torch; a portable filler wire feed torch; a hot wire switching power source for energizing said TIG arc torch, said filler wire feed torch and a base metal; a filler wire feeding device for feeding the wire to said wire feed torch at a desired rate; a welding condition control device for controlling the welding conditions, the welding conditions being determined by parameters including an arc current, a wire feed rate and a power coefficient; and a voice identification-control device for identifying an aural signal from a welder to set the welding conditions and transmitting same to said welding control device.

[006] Patent No. EP 0139249 B1, Filing date: September 26, 1984. Publication date May 2, 1990.

[007] This invention relates to a hot-wire TIG welding (i.e. hot-wire inert-gas tungsten arc welding) apparatus. In this investigation the applicant (Babcock – Hitachi Kabushiki Kaisha) claims a hot-wire TIG welding apparatus comprising an electric power source for providing a TIG arc, another electric power source for feeding a wire-heating electric current to a wire by effecting alternatingly both the feed and pause of electric power so as to heat the wire, a TIG arc torch for feeding wire, characterized by control means having: means (22 and 23; 43; 58) for providing an electric signal proportional to a feed speed of wire; detecting means (25; 35; 36 and 43; 35, 36 and 58) for detecting wire electric current and wire voltage to detect wire-heating instantaneous electric power, said detecting means providing an electric signal corresponding to the detected instantaneous wire-heating power; and comparing-and-controlling means (27, 43, 55 and 58) and a switching element (31, 42 and 54) provided in a circuit of wire-heating electric power feed, said comparing-and-controlling means comparing the electric signal of the wire-heating instantaneous electric power with the electric signal proportional to the feed speed of the wire so as to control the time duration of electric power fed through the switching element on the basis of the result of the comparing so that the wire-heating electric power corresponds to the feed speed of the wire, the feed of wire heating current is paused when the arc current reaches a peak level, the wire heating current being fed when the arc current becomes a base level, the time duration of feed of the wire heating current being not longer than the time duration of the arc base current.

[008] EP 0316936 B1 relates to an unconsumable-electrode welding apparatus comprising an unconsumable electrode (5) arranged in opposed spaced relationship with a base metal (6) to be welded, an AC arc welding power supply (2) connected between the base metal (6) and the unconsumable electrode (5), a filler wire (9) fed toward an arc-generated part formed between the base metal (6) and the unconsumable electrode (5), wire feeding means (8) for feeding the filler wire (9), and
???an AC TIG welding apparatus comprising a wire-heating power supply (3) for energizing the filler wire (9), characterized in that the wire-heating power supply (3) heats the filler wire (9) by supplying thereto a pulsed current in synchronism with the phase of the AC arc current iA formed between the unconsumable electrode (5) and the base metal (6), the filler wire (9) is heated by being supplied with a wire heating current iW during the period when the unconsumable electrode (5) is kept negative in polarity by an AC arc (7) formed between the unconsumable electrode (5) and the base metal (6), and selected one of the operations of stopping the wire-heating current iW and heating the filler wire (9) by supplying thereto a sufficiently small current not to cause any substantial magnetic blow during the period when the unconsumable electrode (5) is kept positive in polarity by the AC arc (7).

[009] EP 0904173 A1 relates to The filler wire in hot wire-gas tungsten arc welding (HW-GTAW) apparatus is heated to near the melting point by application of the hot wire current over a determined length sufficient that the current required is low enough to avoid significant arc blow. This predetermined length of filler wire which approaches the molten state is supported by a ceramic sleeve which in turn may be protected by a stainless steel sheath.

OBJECTS OF THE INVENTION:

[0010] An object of the invention is to propose a fully mechanized HW-GTAW process for producing dissimilar tube butt joints of Alloy 617 and Alloy 740H.

[0011] Another object of the invention is to propose a fully mechanized HW-GTAW process for producing dissimilar tube butt joints of Alloy 617 and Alloy 740H, which improves 200% productivity.

[0012] A still another object of the invention is to propose a fully mechanized HW-GTAW process for producing dissimilar tube butt joints of Alloy 617 and Alloy 740H, which eliminates the requirement of skilled welder.

[0013] A further object of the invention is to propose a fully mechanized HW-GTAW process for producing dissimilar tube butt joints of Alloy 617 and Alloy 740H, which improves the quality of the weld joint with reference to soundness, mechanical and metallurgical properties as well as reduction in defects.

[0014] 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:

[0015] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus/composition 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.

[0016] The invention relates to mechanized Hot Wire GTAW technique for dissimilar weld joints of Alloy 617 and Alloy 740H tube. More particularly, the invention relates to an improved HW-GTAW process for dissimilar material tube butt joints of solid solution strengthened Nickel based super alloy 617 and precipitation hardened nickel based super alloy 740H.

[0017] According to the present invention, there is provided an improved HW-GTAW process for producing dissimilar material tube butt joints of solid solution strengthened Nickel based super alloy 617 and precipitation hardened nickel based super alloy 740, wherein the welding is carried out at 1G position by multi pass deposition without preheating from one side at V-groove butt joint having included an angle of 75o without root face and root gap.

[0018] 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.

[0019] 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.

[0020] 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 DRAWING:

[0021] 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:-

Fig. 1 shows: The schematic diagram of weld groove of the present invention.

[0022] 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 INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWING:

[0023] 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.

[0024] The present invention makes a disclosure regarding a technology pertaining to invention directing to Improved HW-GTAW process for producing dissimilar material tube butt joints of super alloy 617 and 740H.

[0025] Welding passes are nothing but the flow of the welding process or the sequence in which welding should be carried out.

[0026] The welding sequences are known as welding passes. A typical welding process comprises four passes. They are Root Pass, Hot Pass, Fill up Pass and Capping.

Types of Welding Passes:--

Root Pass:
[0027] Root pass refers to the first pass in any welding process, which combines two pieces or members into one structure. Subsequent passes increase the weld depth to the desired thickness, yielding the necessary strength. The first pass usually provides the base for subsequent filler passes.

[0028] Let’s consider a root pass on a set of pipes. The root pass is welded with a technique called push pull method The tip of the electrode is held between both tubes and moved around the circumference of the pipe, advancing vertically downward.

Hot Pass:
[0029] After completing the root pass welding, the welding impurties over the weld bead is adequately removed by wire brushing.

[0030] Next in the sequence that needs immediate action is the “hot pass”.

[0031] When the root (first) pass doesn’t go just as desired, a hot pass may be in order. The Hot pass is a process that helps smoothen or resurface the already done root pass and makes it usable without grinding and cleaning up the weld. The hot pass should not be too hot; rather, it should have few amps above the root pass. These little extra amps will help melt out the top of the root pass and restructure the convex weld into a concave form.

Fill Up Pass:
[0032] To fill the bevel portion, the pass that is made is known as a “fill up pass”.
[0033] It is also referred to as a fill pass as it is the amount of weld bead necessary to fill the weld joint. This pass comes after the root pass or hot pass and before the cap pass or capping.

Capping:
[0034] When the bevel is filled correctly, subsequent passes are made, known as reinforcement passes, also known as “capping”. Capping is the end process in a weld sequence. Capping may be completed either in a stringer bead or by a back-and-forth weaving motion.

[0035] The basic procedure to determine the number of welding passes required is by the following the Welding Procedure Specification. But, in case there is no mention of the necessary number of passes, one is free to use the number of passes depending upon one’s skills and the following factors:

They are:
[0036] Travel Speed – Travel speed is directly proportional to the number of welding passes. Higher the travel speed, lower the weld volume and more the number of passes.

[0037] Width of the weave (oscillation) – It works in a way like the travel speed.

[0038] Joint configuration – A bevel groove needs more passes than a V-groove, keeping other conditions constant.

[0039] Electrode diameter – Larger electrode diameter increases the volume per pass and decreases the number of passes.

[0040] The present invention is fully mechanized HW-GTAW technique for dissimilar joining of the tube to tube butt joint.

[0041] The welding is carried out by multi-pass deposition from one side at V groove butt joint having included an angle of 75o without root face and root gap.

Welding of the invention is carried out under the following conditions:

Filler Material : YT 304H (Dia. 1mm)

Shielding composition Gas : 99.98 and above
Flow Rate : 14 - 16 litres/min

Purging Gas Flow Rate : 4 – 4.5 litres/min

Preheating Temperature : Nil

Inter-Pass Temperature : Less than 100oC

Welding Position : ‘1’ G

Tungsten Electrode Diameter : Dia 3.15 mm (2% thoriated)

Welding Parameters for tube to tube dissimilar butt weld joint of
Alloy 617 and Alloy 740H according to the invention are given herein under.

S.No. Weld
Layer

Weld
Pass Welding Parameters
Hot Wire
Feed Rate Filler Wire
Stick out Hot Wire
Current Welding/
Mean Arc
Voltage Travel
Speed,S
m/min Mm I (A) Current 1(A) V cm/min
1 I 1 1.8 – 2.0 30 – 35 45 – 50 125-135 10.5-12.1 11 -12
2 II 2 1-8 - 2.0 30 -35 45- 50 120-130 11.9-12.9 12 - 13
The process of present invention can be applied for welding of the boiler components.

ADVANTAGES OF THE INVENTION:

- Improves 200% productivity;
- Eliminates the requirement of skilled welder;
- Improves the quality of the weld joint with reference to soundness, mechanical and metallurgical properties as well as reduction in defects.

TEST RESULT:
Radiography test was conducted and it was satisfactory.

[0042] 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.

[0043] 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.
[0044] 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 analogues 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”.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.
, Claims:WE CLAIM:

1. An improved HW-GTAW process for producing dissimilar material tube butt joints of solid solution strengthened Nickel based super alloy 617 and precipitation hardened nickel based super alloy 740, characterized in that the welding is carried out at 1G position by multi pass deposition without preheating from one side at V-groove butt joint having included an angle of 75o without root face and root gap.

2. The process as claimed in claim 1, wherein the purging gas flow rate and shielding gas flow rate are 4-4.5 litres/minute and 14-16 litres/minute respectively wherein inter-pass temperature is less than 100oC, and wherein the tungsten electrode size is 3.15 mm.

3. The process as claimed in claim 1, wherein the hot wire feed rate, hot wire stick out, hot wire current, welding arc current, arc voltage, and travel speed in the first weld pass are 1.8-2.0 m/min, 30-35 mm, 45-50 amp, 125-135 amp, 10.5 -12.1V, and 11-12 cm/min respectively.

4. The process as claimed in claim 1 or 3, wherein the hot wire feed rate, hot wire stick-out, hot wire current, welding arc current, arc voltage, and travel speed in the second weld pass are 1.8-2.0 m/min, 30-35 mm, 45-50 amp, 120-130 amp, 11.9-12.9 V, and 12 -13 cm/min respectively.

5. The process as claimed in claim 1, wherein the shielding gas has composition of at least 99.98% Argon.