What are the characteristics of welding materials?

It is highly unlikely that any single hazardous factor will be present in isolation during welding operations employing various welding processes; in addition to the primary hazards associated with welding materials, there is also a significant likelihood that several of the aforementioned hazardous factors will coexist. It should also be noted that some hazardous factors exhibit greater toxic effects on the human body than do individual, isolated hazards. Therefore, even when the levels of certain hazardous factors in welding materials appear to be within acceptable hygienic standards, appropriate occupational health and safety measures must still be implemented.

What are the characteristics of welding materials?

(1) The primary focus of research on welding occupational health is fusion welding, with arc welding presenting the most significant occupational health concerns and submerged-arc welding and electroslag welding posing the fewest.

(2) The primary hazardous factors associated with shielded metal arc welding, carbon arc gouging, and CO2 gas-shielded welding include the fumes and dust generated during the welding process. This is particularly true for shielded metal arc welding and carbon arc gouging. When these processes are carried out over extended periods in confined spaces—such as boilers, ship holds, sealed containers, and pipelines—with inadequate occupational health and safety measures, they can pose serious risks to the respiratory system and, in severe cases, lead to welder’s pneumoconiosis.

(3) Toxic gases are the primary hazardous factors in gas welding and plasma arc welding, and high concentrations can cause symptoms of poisoning. In particular, ozone and nitrogen oxides are formed when the high-temperature radiation from the electric arc acts on the oxygen and nitrogen in the air.

(4) Arc radiation is a common harmful factor in all types of arc welding, and the resulting photoelectrical ophthalmia is a specific occupational disease associated with arc welding. Arc radiation can also damage the skin, leading welders to develop dermatitis, erythema, small blisters, and other skin disorders. In addition, cotton fabric fibers may be damaged.

What are the precautions for welding materials?

1. Stainless steel welding electrodes are generally available in two types: titanium-calcium and low-hydrogen. Whenever possible, direct current should be used for welding, as this helps prevent the electrode from overheating and melting too deeply. Titanium-calcium coated electrodes are not suitable for all-position welding; they are best used for flat and fillet welds only. Low-hydrogen coated electrodes, on the other hand, can be used for all-position welding.

2. Stainless steel electrodes must be dried before use. To prevent defects such as cracks, depressions, and porosity, titanium-calcium coated electrodes should be dried at 150–250°C for 1 hour prior to welding, while low-hydrogen coated electrodes should be dried at 200–300°C for 1 hour before welding. Repeated drying is not permitted, as this can easily cause the coating to flake off.

3. Clean the weld joint thoroughly; ensure that the welding electrode does not come into contact with oil or other contaminants, as this can increase the carbon content of the weld and compromise weld quality.

4. To prevent intergranular corrosion caused by overheating, the welding current should not be too high—typically about 20% lower than that used for carbon steel electrodes—and the arc length should be kept short. If the floor cools rapidly, narrow welds are more appropriate.

5. When drawing arcs, do not initiate the arc from an unwelded area; therefore, it is best to use an arc plate made from welded components or similar materials to establish the arc.

6. Short-arc welding should be used whenever possible. The arc length is typically 2–3 mm; an excessively long arc can easily lead to hot cracking.

7. Welding in the cloud: Short-arc, rapid welding should be employed, and lateral weaving is generally not permitted. The purpose is to minimize heat input and the width of the heat-affected zone, enhance the weld’s resistance to internal corrosion, and reduce the tendency for hot cracking.

8. When welding dissimilar steels, carefully select the electrode to prevent inappropriate hot cracking or embrittlement of the metal caused by high-temperature heat treatment. Refer to the selection criteria for electrodes used in stainless steel and dissimilar steel welding, and adopt appropriate welding procedures.