1. PLASMA ARC WELDING ( PAW) Is an arc welding process similar to gas tungsten arc welding (GTAW). Plasma arc welding is an arc welding process wherein coalescence is produced by the heat obtained from a constricted arc setup between a tungsten/alloy tungsten electrode and the water-cooled (constricting) nozzle (non- transferred arc) or between a tungsten/alloy tungsten electrode and the job (transferred arc).coalescence The process employs two inert gases, one forms the arc plasma and the second shields the arc plasma. Filler metal may or may not be added.

2. PLASMA ARC WELDING (PAW)

3. The electric arc is formed between an electrode (which is usually but not always made of sintered tungsten) and the workpiece. The key difference from GTAW is that in PAW, by positioning the electrode within the body of the torch, the plasma arc can be separated from the shielding gas envelope. The plasma is then forced through a fine-bore copper nozzle which constricts the arc and the plasma exits the orifice at high velocities (approaching the speed of sound) and a temperature approaching 28,000 °C (50,000 °F) or higher. against about 5500 °C (10000 °F) in ordinary electric welding arc.

4. Just as oxy-fuel torches can be used for either welding or cutting, so too can plasma torches, which can achieve plasma arc welding or plasma cutting. Arc plasma is the temporary state of a gas. The gas gets ionized after passage of electric current through it and it becomes a conductor of electricity. In ionized state atoms break into electrons (−) and cations (+) and the system contains a mixture of ions, electrons and highly excited atoms. The degree of ionization may be between 1% and greater than 100% i.e.; double and triple degrees of ionization. Such states exist as more electrons are pulled from their orbits.

5. The energy of the plasma jet and thus the temperature is dependent upon the electrical power employed to create arc plasma. Actually all welding arcs are (partially ionized) plasmas, but the one in plasma arc welding is a constricted arc plasma.

6. PIPE WELDING

10. TECHNIQUES, POSITIONS & PROCEDURES Joining curved pieces of metal is more difficult than welding flat sheets, so by far the most challenging process you’re ever likely to come across is pipe welding, where you will be required to join cylindrical metal tubes using either SMAW or gas shielded arc welding processes. The pipe welding positions and techniques are often quite uncomfortable, especially if the pipe is fixed and access is restricted.

11. As a result, before you even think about tackling pipe welding, it’s important to perfect the art of plate welding first. Learning the structural welding basics will give you a much better understanding of welding in general, which is a great foundation for more complex procedures. As pipe welding is so difficult, welders who excel at this skill tend to earn higher salaries than those employed to use other welding techniques. As a result, the 6G pipe welding certification is one of the most sought-after certifications in the industry.

12. PIPE WELDING BASICS If a welding joint does not use a tacked backing plate, it’s known as open root welding, which is the most common process used while pipe welding. This is particularly difficult because you’ll essentially be welding across a gap (albeit a small one) so it’s important to use the right technique so that you don’t make a mess of the whole job Every welder will have a ‘good’ side and a ‘bad’ side when it comes to welding, depending on whether they’re left- or right- handed. Think about it: as you move around the pipe, at some point your hand will be blocking your view.

13. For right-handed welders the left-hand side of the pipe is the challenge; for left-handed welders, it’s the right-hand side of the pipe which is the most difficult. Anticipating this obstacle and learning how to overcome it is the best way to ensure super strong, neat welds every time. Always remember that gravity will have an effect on the

14. weld pool, so whichever is your strongest hand, the bottom half of the pipe will probably be more challenging than the top. It’s a good idea to start by tack welding your materials together, as this will hold them in place securely, allowing you to take time and care over welding properly. Whenever you start and stop pipe welding, always do so on the side wall – never in the gap. Start the arc, wait for the weld pool to form, then slowly and gently move across the open root to the other side. Slowly zigzag your way along the open root for the first section of the pipe until you have to change your position.

15. Think of the pipe in terms of a clock face, and divide it up into sections. Start at the 12 o’clock position, and work round to 3 o’clock, then stop and make sure you’re comfortable and prepared for the next section, and repeat this process until you’ve completed the entire weld. Pipe welding often uses quite thick, heavy duty materials, and the open root nature of the welds means that penetration can be poor if not done properly.

16. Leaving poorly penetrated welds on tough, industrial pipe welding jobs can be disastrous. You’ll need to ensure that you achieve full penetration, but given that it’s unlikely that you’ll be able to weld from the inside of the pipe as well as the outside, you can combat this potential problem by using a groove weld

17. PIPE WELDING POSITIONS There is a system of letters and numbers which acts as a code to indicate which joint type and position to use. Fillet welds do exist with pipe welding, but they’re very uncommon: they’re indicated by the letter F. Far more common are groove welds, which you can identify with the letter G. There are four main pipe welding positions, numbered 1, 2, 5 and 6. The 1G position isn’t used very often, but it’s still important to recognize it. This is pretty much just flat welding because the pipe will be lying on its side (on the curved edge) and can be rotated as you weld.

19. I you come across the letter R in pipe welding codes, this indicates a restricted welding position, which can either be physically or visually.

20. The 2G position is fixed, which means that the pipe cannot be turned as you weld. In this case, the pipe is placed on its base, which makes it much sturdier and more stable to weld. The 5G position is similar to 1G in that the pipe is placed horizontally, except that it is fixed and cannot move. This will require you weld in a variety of different positions, including overhead. Vertical up and vertical down directions – which are both used in this position – are techniques which have specifications set up the ASME and API.

21. The 6G position is the most challenging because it involves the pipe being fixed at a 45º angle. This requires welding in all positions and incorporates the ‘good’ and ‘bad’ sides that were discussed earlier.