Operation Precautions for Shielded Metal Arc Welding      (1) Maintain a proper arc length during welding. An excessively long arc will cause arc instability, reduced penetration, increased spatter and severe oxidation.      (2) Do not cut off the arc immediately upon finishing each weld pass. Fill the crater completely or lead the arc to the outer side of the weld.      (3) For multi-pass welding, the thickness of each layer shall be 0.8 ~ 1.2 mm. Thoroughly remove slag on the weld surface before welding the next layer. Stagger the joints between layers when replacing electrodes.

     (4) For double-sided welding, after completing the front side, remove incomplete penetration and slag on the back side with an air chisel or carbon arc gouging. Grind or wire-brush the surface thoroughly before welding.      (5) Clean off rust, oil and other contaminants from the welding area before operation.      (6) If the groove gap of assembled workpieces is too large and cannot be adjusted, do not insert iron strips or similar materials. Build up weld beads on both sides of the joint first, then proceed with formal welding.      (7) Stop welding if the work is exposed to wind, snow or rain during the process.      (8) Inspect each weld visually after completion. If defects such as pores, slag inclusions or weld beads are found, remove them completely and perform repair welding.      (9) When welding critical equipment and pipelines, use the same type of electrode for tack welding as for formal welding. Control arc striking and tack welding positions to avoid scratching the base metal.