Handbook-Fusion Welding Carbon

1 WELDING CARBON STEEL Low-carbon mild steel is not only the most widely used metal; it is also the easiest to weld. Although most steel welding is done today with coated electrodes, or by one of the consumable-wire arc welding processes, oxy- acetylene welding of steel, especially in thicknesses of 1/4 in. (6 mm) or less, is still widely employed. A well- trained oxy-acetylene welder, working on steel 1/8 in. (3 mm) thick, can usually make welds of better quality than can the average arc welder, and make them almost as rapidly. Once you have mastered the art of welding steel, you are ready to tackle some of the metals which are more difficult to weld. Steel should always be the starting point. In this chapter, the specific instructions for welding will be given in the form of captions accompanying Fig. 13-1 through 13-19. Fig. 13-1 through 13-4 deal with welding of sheet, Fig. 13-5 through 13-12 with the welding of plate, Fig. 13-13 through 13-19 with the welding of pipe. If you are teaching yourself to weld from this book, without the aid of a good instructor, we urge you to work your way through Fig. 13-12, in sequence, then decide whether or not you wish to tackle pipe. However, if you are definitely interested in learning to weld steel pipe, and feel that you are doing well after getting through Fig. 13-6, you may properly skip from Fig. 13-6 to Fig. 13-13, assuming that you can secure an adequate supply of properly-bevelled pipe, 2 to 4 in. in diameter. *In previous editions of this Handbook, the welding of steel sheet, steel plate, and steel pipe were covered in separate chapters. For two reasons, we have elected to treat the welding of steel in one continuous chapter in this edition. The first is this: In previous editions, the technique of flame and rod movement recommended for welding sheet was quite different from that recommended for welding plate and pipe. That technique is still valid, especially for the welding of the thinnest sheet (less than 1/16 in., or 16-gauge), and will be covered at the close of this chapter. In most situations, however, the same technique used for welding plate and pipe can be used for welding sheet, and it is easier to master. The second reason concerns pipe welding: Earlier editions of the Handbook treated pipe welding chiefly in terms of rather large-diameter pipe, which is seldom oxy-acetylene welded today. Oxy-acetylene welding of pipe is today largely restricted to pipe sizes ranging from 1/2 in. to 4 in. The technique used for welding pipe in those sizes is essentially no different than that used for welding plate or sheet of equivalent thickness.