FIELD OF THE INVENTION
The present invention relates to welding of high pressure high thickness pipe. In particular, the invention relates to a method of effecting purging and sealing of pipes filled with inert gas for welding. More particularly, the invention relates to a method of optimum purging in a conventional root welding process of ferritic chrome moly steel pipes.
BACKGROUND OF THE INVENTION
A dosed stationary installation for transporting/distribution fluids like steam and water in super critical boilers is known as steam generator package links. These steam generator package links are made up of high thickness pipes having outside diameter of about 610mm with thickness around 100mm. The material used is specially designed "Creep Strength Enhanced Ferrite Chrome Moly Steel". These pipes are butt welded using root GTAW processes, SMAW hot passes and with subsequent SAW fillings.
Root GTAW welding processes is highly critical which is welded with a minimum preheat temperature of 150°C, which Induces multiple root defects like porosity, 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 Post Weld Heat Treatment (PWHT). If the defect is not addressed, repair welding is induced which calls for another preheating-welding-PWHT cycle. Purging of the atmospheric air inside the pipe is required to prevent oxidation during welding. The prior art method/technique used for root purging with inert gas is found to be ineffective to prevent the root weld from defects. According to the prior art, both the ends of the pipes were closed with temporary end covers and inert gas is sent from one of the end cover through a 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. Accordingly, the Non Destructive Test (NDT) exhibits the requirement of repair and rework. More time is consumed for bevel grinding, again and again pre-heating, Arc welding, NDT, Stress relieving. This is one of the reasons for more cycle time in the prior art method of root welding of pipe to pipe weld joints.
Hence there is a necessity to find out an alternate method of sealing system for perfect sealing, ensuring cent percent purging.
WO2015141246A1 entitled "Purge apparatus and purge method", which teaches that a nozzle is used in the apparatus from obstructing of a container without using an actuator. In 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 thereby the container is aligned by means of the aligning member, and then a purge gas is injected to the container from the.nozzle.
US9103285B2 entitled "Purge system, system including a purge system, and purge method", discloses a purge system and liquid atomizing, a system including a purge system and liquid fuel atomizing system, and a method of purging and atomizing. 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.

OBJECTS OF THE INVENTION
It is therefore an object of the invention is to propose a method of optimum purging in a conventional root welding process of ferritic chrome moly steel pipes, which avoids root defects in butt joint welding of steam generators package links.
Another object of the invention is to propose a method of optimum purging in a conventional root welding process of ferritic chrome moly steel pipes, which reduces the cycle time of the link fabrication especially in butt joint welding.
A further object of the invention is to propose an improved purging system to prevent oxidation during welding ensuring Cen percent purging.
SUMMARY OF THE INVENTION
Considering the requirement of sound root weld, the technique an improved method and apparatus have been provided. Accordingly, the work piece (01) and work piece (02) are taken and cleaned for rust. The sealing sheet (06) which has a sealing sheet puller (10) 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.
As per the welding requirement of the Cr-Mo steel the minimum required pre¬heating is maintained. Then the other end of work piece (02) is sealed with the special arrangement. The special arrangement includes the metal end cover (03), with outlet valve (04) to maintain the flow rate and build in pressure and inlet connector (05) which takes the inert gas to the welding zone. We use a specially

designed Aluminium foil tape (11) which sticks to the surface of the pipe at the butt joint even at the elevated pre-heat temperature to increase the efficiency of the sealing. Then the welding of root with conventional GTAW is proceeded with trained welders and after the finish of the weld the sealing sheet (06) is pulled out with the sealing sheet puller (10). This complete arrangement is re-used for jobs with same dimensions.
This technique 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.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Rg-1 shows the arrangement of end cover with inlet and outlet connections.
Fig-2 shows the sealing sheet with connectors and lock in position.
Fig-3 shows the purging system with cylindrical pipes to be circumference root welded.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
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. One end consists of inlet and outlet valve with metal end cover for gas inflow and out flow and to weld end is fully dosed.
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 shows the different parts of the device with metal end cover (03) and welded with outlet valve (04) to maintain the flow rate and inlet connection (05) welded to inert gas - the gas to the welding area from gas cylinder with control valves(06) is center diameter 10mm hole provided .its sealing sheet puller (10)and sealing sheet washer (09)with sealing sheet lock nut (08)also tightened, then horizontal work piece (01) to perfect seating the sealing sheet (06).
Figure -2 shows the whole assembly (consisting of 01, 06 and 07) is placed at a distance of 200mm from the end of the work piece (01) where the root joint is to be carried out.
The maximum outside diameter of the workspace is 610mm and thickness of the pipe is 100mm and these pipes are used as steam generator package links.

WE CLAIM :
1. A method of optimum purging in conventional root welding process of ferritic chrome moly steel pipes, the method comprising the steps of:
cleaning a first work piece (01) and a second work piece (02) for removal of rust, and placing a the sealing sheet (06) having a sealing puller (10) from inside of the first work piece (01) near the butt joint at a distance of about 200mm and seating in a tapered portion;
locating the first and second work pieces (01),(02) together at a desired root gap (2mm) as per the welding procedure, including an aluminium foil tape (11) which sticks to the inner surface of the joinable location at the butt joint area;
sealing the second end of the work piece (02) with a metal end cover (03, 04,05) respectively;
relasing an inert gas from a source (12) with a regulator mounted there on and cent per cent evacuation of atmospheric air is ensured by out flow of the inert gas through an outlet valve (04);
carrying out the root welding under the optimum inert atmosphere with the sealing between the first and second work pieces (01,02) and obtaining a sound joint with the progress of welding the aluminium foil tape getting fused;
wherein a pre-heating is maintained at a temperature of minimum 150° C to 220° C for carrying out the submerged arc welding.

2. The method as claimed in claim 1, wherein the size of the sealing seat (06) and the end cover (03) can be varied according to the diameter of the pipes which are to be root welded.