Abstract: This paper presents a new way for designing and manufacturing small size plasma arc welding torches.A method of controlling the plasma arc direction has been developed,enabling the torch to produce plasma arc in a direction at any desirable angle to its axis,For steel tubing of inside diameter from 12 to 20 mm,internal bore butt welding and fillet welding can be successfully done with such a torch.Both the appearance and the quality of weld are satisfactory.The advantages of this new infernal bore plasma arc welding process are longer life of tungsten electrode,low argon consumption rate,and so forth.It is a new and economical internal bore welding process for steel tubing of small size.