This Standard specifies the automatic or manual ultrasonic examination on the welds of carbon steel pipes and ferritic alloy steel pipes (hereafter,referred to as "steel pipes") whose internal and external surfaces are arc welded automatically in longitudinal direction or in spiral state,and which are 350 mm or over in outside diameter and 6 mm or over in wall thickness.Usually,this is applicable to the examination of flaws oriented parallel to the weld line.