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Welding porosity refers to the presence of small cavities or pores within the weld metal. These cavities are essentially trapped gas bubbles that remain within the weld as it solidifies, which can weaken the joint and reduce its overall strength. In appearance, porosity looks like small holes or bubbles on the surface or inside the weld bead.

Causes of Welding Porosity
Contaminants on the Base Metal

Cause: Contaminants like oil, grease, moisture, dirt, or rust on the welding surface can vaporize due to the high heat, producing gases that get trapped in the weld.
Prevention: Properly clean and prepare the metal surface before welding by removing any contaminants to reduce the likelihood of porosity.
Moisture in the Filler Material or Electrode

Cause: If filler material, electrodes, or fluxes contain moisture, the heat of welding can cause the moisture to vaporize into hydrogen, forming pores as the weld solidifies.
Prevention: Store filler materials and electrodes in a dry environment, and use proper storage containers or ovens to prevent moisture absorption.
Shielding Gas Issues

Cause: In gas-shielded welding processes like MIG or TIG, shielding gas protects the weld pool from atmospheric contamination. Issues like incorrect gas flow rate, leaks, or drafts can allow air to mix with the shielding gas, causing porosity.
Prevention: Use the recommended shielding gas flow rate, check for leaks, and avoid welding in windy areas without protective barriers.
Improper Welding Technique

Cause: Techniques like holding the torch too far from the weld pool, or welding at improper angles, can reduce the effectiveness of the shielding gas, allowing oxygen or nitrogen from the atmosphere to contaminate the weld.
Prevention: Use consistent techniques, maintain the recommended distance and angle, and ensure the shielding gas fully covers the weld pool.
High Sulfur or Carbon Content in the Base Metal

Cause: Metals with high sulfur or carbon content can produce gases when heated, leading to porosity.
Prevention: Choose base metals that are compatible with the welding process and filler material, and consider preheating to reduce the risk of gas formation in certain metals.
Excessive Heat or High Welding Speed

Cause: High welding speed can trap gas before it has time to escape, while excessive heat can cause more gases to form in the weld pool, increasing porosity.
Prevention: Adjust the heat settings and welding speed to ensure proper fusion and allow time for gases to escape from the weld pool before solidification.