FIELD OF THE INVENTION

The present invention relates to a method for welding of high pressure high thickness pipe, more particularly the method is using of purging revered for welding pipe line by perfect sealing of pipes.
BACKGROUND OF THE INVENTION
In a steam power station, the electrical energy is produced according to the principle of “external combustion,” where the “heat of combustion” of the fuel is transferred to a prime mover by a “working medium.” In the steam generator, low-temperature water is the working medium that receives the heat of combustion of fuel and becomes high-energy steam. The heat of steam is converted to mechanical energy in the steam turbine and then to electrical energy in the generator.
Moreover, specified and heavy weight pipe are used in boiler construction as well as steam generator and while construction, the super-heated header and main steam line are inter connected with the help of pipe butt joint. In the conventional method of butt joint fit-up welding of pipes is discussed as below. The closed stationary installation for transporting/distribution fluids like steam and water in super critical boilers named as stream generators package links. These steam generator package links and headers are made up of high thickness pipes having outside diameter 273 to 610mm with thickness 36 to 100mm. The material used is specially designed “Creep Strength Enhanced Ferrite Chrome Moly Steel”(Gr. P91 and P92 material). Butt joining of these pipes are welded by using root GTAW (Gas tungsten arc welding) processes, SMAW (Shielded metal arc welding) hot passes and with subsequent SAW (Submerged arc welding) fillings.
Further, Root GTAW welding processes is highly critical which is welded with a minimum preheat temperature of 150° C. It induces lot of root defects like porous, worm holes and root oxidation. This is due to the higher percentage of chromium and other micro alloying elements. These defects are removed by mere grinding with abrasive grinding wheels which is done after the PWHT (Post Weld Heat Treatment). If said defects are not addressed, repair welding is induced, which calls for another preheating-welding-PWHT cycle. The method/technique used for root purging with inert gas was ineffective to prevent the root weld from defects. Both the end of the pipes was closed with temporary end covers and inert gas is send from one of the end cover through the small hole drilled on the end cover. This dilutes the effect of the purging, which is proportional to the length and inner diameter of the pipes, which is not at all effective

at the root during welding, and NDT (Non-destructive testing) result in repair and rework. More time consumed for bevel grinding, again and again pre-heating, Arc welding, NDT, Stress relieving. This is one of the reasons for more cycle time required.
Prior Arts:
There are a few prior arts found related to the present invention as discussed below.
WO2015141246A1 disclosed as to prevent a nozzle from obstructing of a container without using an actuator. In the case where the nozzle comes into contact with the container before an aligning member comes into contact with the container, the container is guided by means of a guide surface of the nozzle, and at the same time, the aligning member and the container are brought into contact with each other by bringing down the nozzle by means of a load from the container, and the container is aligned by means of the aligning member, then a purge gas is injected to the container from the nozzle. The cited prior art document disclosed that without using an actuator, the nozzle is to make it not interfere with the positioning of the container which includes with a gas inlet holes to accommodate the articles and the bottom, a purge device for purging by the purge gas.
US9103285B2 is talked about a purge system and liquid atomizing, a system including a purge system and liquid fuel atomizing system, and a method of purging and atomizing are disclosed. The purging involves a first nozzle, a second nozzle, a third nozzle, and a staged compression system having a first stage and a second stage. The first stage is configured to selectively direct a first pressurized fluid stream to the first nozzle. The second stage is configured to selectively direct a second pressurized fluid stream to the third nozzle.
201631018499 is talked about a method of optimum purging for conventional root welding
process of ferritic chrome moly steel pipes.
The cited prior art disclosed a purge system decided to close of inlet and outlet valve with metal end cover for gas inflow and out flow. And other end is fully closed. And inert gas volume pf pipe length 6.1m.
The above prior arts as disclosed above are not same as solution disclosed in the present invention.

Disadvantages:
In the conventional method of purging welding is following disadvantages: ineffective purging at the butt joint location since argon being heavier than air, wastage of the high cost inert gas argon, more release of argon to the atmosphere pollutes the working atmosphere, re-welding is required in case of thickness reduction, additional stress relieving in case of welding due to thickness reduction, additional Radiographic Testing required, the conventional method is more laborious, unsafe and required more cycle time.
Hence, there is a need to find out an alternate method of sealing system for perfect sealing, ensuring cent percent purging with advantages.
OBJECTS OF THE INVENTION:
The objective of the invention is to avoid root defects in butt joint welding of stream generators package links.
Another object of the present invention is to propose a purging method for welding steel pipes by using butt joint root welding used in steam generators package links.
Yet another object of the present invention is to provide reduced cycle time of the link fabrication especially in butt joint welding.
Still another object of the present invention is to achieve effective purging by reducing area of purge while welding P91/P92 Grade pipe butt joints.
SUMMARY OF THE INVENTION:
One or more drawbacks of conventional arts for welding of pipe line links and headers are overcome; and additional advantages are provided through the present invention as disclosed. Additional feature 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. In the conventional welding method used in pipe line links and headers with high pressure and high temperature lines are more prone to leak or crack. To overcome this the P91/P92 Grade material (ferritic chrome poly steel sheet pipes) are used. In the present invention, it is mandatory to purge while two such material pipes are joined.

In an embodiment, a purging method for welding of high pressure high thickness pipes used in stream generators package links, the method comprising: taking first work piece after cleaning the rust, followed by placing the sealing sheet that has a sealing puller chain, from inside the work piece near the butt joint; taking second work piece after cleaning the rust, followed by placing the sealing sheet with a metal flow tube assemble, from inside the work piece near the butt joint; bringing both the work pieces together with a predetermined root gap for butt joint fit up; releasing argon gas from the cylinder through the flow tube into joinable portion of first work piece and second work piece in the purged area; starting root welding with TIG (Tungsten inert gas) method and after completion of root and two layer welding, the flow tube assembly is pulled out from one end and also sealing template is pulled out by using chain; and moving the welded work pieces to submerged arc welding station to complete welding of balance layers and further for stress relieving and then nondestructive testing.
In another embodiment, the length of work pieces using in the welding process is in the range of 5m to 20m and the length of the work pieces is 6m, used in the purging method. The work piece has a sealing sheet with metal flow tube an inert gas orifice with connected by gas hose connector and argon gas cylinder with control valve.
In another embodiment, the aluminum foil tape is sticked inside the sealing sheet within the purge area to arrest the root gap in turn to maintain the preheat temperature with minimum 150°C. The preheat maintaining temperature is in the range of 150°C to 220°C for carrying out the submerged arc welding.
Other objects, features and advantages of the present disclosure will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
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 shrouds that are consistent with the subject matter as claimed herein, wherein:

Fig-1 illustrates the arrangement of metal flow tube with inlet and outlet orifice according to the present invention.
Fig-2 illustrates the gas orifice.
Fig-3 illustrates the sealing sheet with connector, lock and sealing sheet puller according to the present invention.
Fig-4 illustrates the purging system with cylindrical pipes to be circumference root weld according to the present invention.
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 illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION OF THE INVENTION:
The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, “consisting” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the

presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
According to the present invention, the root welding is carried out by positioning the work pipes in the device with suitable sealing sheet insert the butt joint area and opposite end closed the metal end cover at the placed. We have to make proper purging method, we decided to close both ends of the pipe .one end consists of inlet and outlet gas orifice with metal flow tube for gas inflow and to weld end is fully closed.
So arrangement of such purging improves the quality requirement of the component during service condition also it improves the productivity by means of avoiding rework and repair.
Figure -1 illustrates the different parts of the device. A metal flow tube (03) is taken in which one end is considered as inlet. In inlet side an orifice is inserted (04) and welded circumferentially and the other side is considered outlet in which an outlet orifice (13) is inserted and welded circumferentially. On outlet side, a round sealing sheet (08) as per the internal diameter of the pipe is fixed by means of a center hole in sheet and tightened by a sealing sheet washer (15) and a sealing sheet locking nut (14). A hose connector (05), (12) from argon gas cylinder (07) through control valve (06) is connected to inlet side of the orifice (04).
Figure -2 illustrates the inlet and outlet orifices (13). Orifice one end is of press fit type and the other end is of external threaded. In the middle, raised portion is used to support and for welding purpose. Orifice has internal hole to allow the gas to flow through.

Figure -3 illustrates the sealing sheet assembly on the other end of the pipe. Sealing sheet (09) is of circular in dimension as per the internal diameter of the pipe. A radial hole is made at the center of the sheet and press fitted inside the pipe (01). A washer (16) and a sealing sheet connector (10) is used to fix the sealing sheet puller (11) with the sealing sheet. It is used to pull out the sealing sheet after completion of welding.
The present invention is directed to a method for welding of high pressure high thickness pipe as per the requirement of sound root weld as illustrated in fig -4. Figure -4 shows the whole assembly of the invention. The work piece (01) and work piece (02) are taken and cleaned for rust as shown in the figure-4. The sealing sheet (09),(10) is made from 0.75mm GI sheet, so while pulling, it will shrink and will be easily removed by pulling the chain. Moreover, the chain has a sealing sheet puller (11) is placed from inside of the link pipe (01), near to the butt joint. Then both the work piece (01, 02) are brought together with required root gap, as per the welding procedure. After welding process completed, pull out the chain assembly with template again and again using for further joints.
In the present invention, the method of welding is described herein as shown in the figure-4. As per the welding requirement of the Cr-Mo steel, the minimum required pre-heating is maintained. On the other end of work piece (02) is sealed with the special arrangement. The special arrangement includes the metal flow tube (03), with inlet and outlet gas orifice (04),(13) to maintain the flow rate and pressure is controlled by a flow regulator (06) mounted with argon cylinder and from inlet connector (04) which takes in the inert gas flow rate move the gas outlet orifice to the welding zone. Usually, an inert gas, such as argon is 1.38 times heavier than air, is used to purge out the atmospheric oxygen (air) from the inside of the pipe. In the present invention, it uses a specially designed aluminum foil tape which sticks to the sealing sheet portion of the assembly in contact with inner surface of pipe is sealed with aluminum foil tape to give sufficient sealing. Surface of the pipe, at the butt joint, even at the elevated pre¬heat temperature, is used to increase the efficiency of the sealing. Further, the welding of root with GTAW is proceeded with trained welders. After the finish of the weld, the sealing sheet (08),(09) are pulled out with the sealing sheet puller (11) along with flow tube (03). This complete arrangement is re-used for jobs with same dimensions.
Moreover, the invention relates to a method of welding ferritic chrome moly steel in butt joint root welding. The method includes at least two work piece (01)(02) having edge prepared opening end of 30 degrees to the horizontal axis with butt joint area. The gas flow

movement arrested by full sealing sheet (09) and sealing sheet washer (16) with locking nut (17) and tightened sealing sheet connector is pulled out with the sealing sheet puller (11). The metal flow tube (03)with outlet orifice (13) with sealing sheet (08) and sealing sheet washer (15) with locking nut (14) and tightened and inlet gas orifice (04) with connected by gas hose connector (05,12) and argon gas cylinder (07) with control valve (06) respectively. The aluminum foil tape, which sticks to arrested the root gap 2mm turn maintained the preheat temperature with minimum 150° C ensure that the root purring with the optimum pressure, flow and purity of the inert gas. The workspace (01) & (02) is ready to carry out the root welding uniformly for the work piece having outside diameter 610mm with thickness of 100mm seamless pipe of having specification ferritic chrome moly steel and weight of work piece is a ton/job.
This method ensures the root purging with the optimum pressure, flow and purity of the inert gas. This in turn ensures the elimination of root defects like porous, root oxidation and worm holes. This is ensured in the NDT results of the butt joint.
For example, two work piece ((01) and (02)) of a length of 6m are taken and cleaned for rust and then sealing sheet is placed inside both the work pieces near the butt joint takes place. The length of the work piece may be in the range of (5m to 20m). The work pieces are the ferrite chrome moly steel pipes (P91/P92). The work piece (01) has a sealing puller chain, placed inside said work piece (01) near the butt joint and after welding, the chain assembly is pulled out. The work piece (02) has metal sheet with a metal flow tube an inert gas orifice (04) with connected by gas hose connector (05, 12) and argon gas cylinder (07) with control valve (06) respectively. The length of the tube is varied, for example 6m. Both the work pieces are brought together with a predetermined root gap of 2mm for butt joint fit-up as per the welding procedure. The aluminum foil tape sticks to the inner surface of the pipes as indicated (tube (05), sealing seats (08) and (09)) to prevent any leakage of argon gas. The argon gas is released from cylinder (07) and enters into the purge area through the flow tube for root welding with Tungsten inert gas method and after the root and two layer welding is completed, flow tube is pulled out from one end, and on the other end, template is pulled out with the help of pulling chain (11). After completion of root welding, the submerged Arc welding process is performed on welded work pieces ((01) (02)). The argon gas is used for welding of both the work pieces only in the 400mm (welding area) only as shown in the fig 4. Since the purged volume is drastically reduced, flow and pressure of purging gas is maintained perfectly and gives defect free root. This is advantage of using the method as disclosed in the present invention. In the

conventional method, gas is filled up inside both the pipes, used for welding both the work pieces, so wastage of high cost inert gas argon has occurred. Once the welding process is finished, the welded work pieces are gone through stress relieving process and after that gone through non-destructive testing process. The butt joints are then subjected to Radiographic test. The test results are shown in below.
This method is only applicable to ferritic chrome poly steel sheet pipes. Other materials pipe lines like Low alloy steels (SA106, P12, P22) purging is not mandatory as these types of materials are free from root defects.
Advantages:
1. In the present invention, it is to achieve effective purging by reducing area of purge while welding P91/P92 pipe butt joints.
2. The method of purging (Argon gas) is required for only 400mm distance of pipe volume, not like previous conventional method of using argon gas cylinders at both pipes (Work piece) of full volume.
3. The method enhances the quality of pipes.
4. Good Radiographic test results are achieved. The test result illustrates the defected pipes and defect-free pipes with and without using the method used in the present invention. The test result shows as below.


WE CLAIM:

1. A purging method for welding of high pressure high thickness pipes used in steam
generators package links, the method comprising:
- taking first work piece (01) after cleaning the rust, followed by placing the sealing sheet (09) that has a sealing puller chain(11), from inside the work piece (01) near the butt joint;
- taking second work piece (02) after cleaning the rust, followed by placing the sealing sheet (08) with a metal flow tube assemble (03), from inside the work piece (02) near the butt joint;
- bringing both the work pieces ((01, 02) together with a predetermined root gap for butt joint fit up;
characterized in that,
- injecting argon gas into joinable portion of first work piece (01) and second work piece (02) in the purged area (18) through the flow tube (05) for performing butt joint welding;
- starting root welding with TIG (Tungsten inert gas) method and after completion of root and two layer welding, the flow tube assembly is pulled out from one end and also sealing template is pulled out by using chain (11); and
- moving the welded work pieces to submerged arc welding station to complete welding of balance layers and further for stress relieving and then nondestructive testing.

2. The method as claimed in claim 1, wherein the method characterized in that the argon gas is injected into the purge area (18) through flow tube (05) for performing butt joint welding.
3. The method as claimed in claim 1, wherein the length of work pieces (01, 02) is in the range of 5m to 20m.
4. The method as claimed in claim 2, wherein the length of the work pieces (01) (02) is
6m used purging method.
5. The method as claimed in claim 1, wherein the work piece has a sealing sheet with
metal flow tube an inert gas orifice (04) with connected by gas hose connector (05,12)
and argon gas cylinder (07) with control valve (06).

6. The method as claimed in claim 1, wherein the aluminum foil tape is sticked inside the sealing sheet within the purge area to arrest the root gap in turn to maintain the preheat temperature with minimum 150°C.
7. The method as claimed in claim 1 and 5, wherein the preheat maintaining temperature is in the range of 150°C to 220°C for carrying out the submerged arc welding.