Standard Operating Procedure: Tungsten Inert Gas (TIG) Welding

This Standard Operating Procedure (SOP) outlines the mandatory safety protocols, equipment preparation, and technical execution required for Gas Tungsten Arc Welding (GTAW), commonly known as TIG welding. TIG welding is a precision joining process that requires meticulous attention to cleanliness, machine settings, and electrode geometry. Adherence to these procedures ensures structural integrity, optimal weld aesthetics, and the safety of the welding operator. All personnel must hold current certification or receive direct supervision from a qualified lead welder before attempting these procedures.

1. Safety and Personal Protective Equipment (PPE)

• Respiratory Protection: Ensure adequate local exhaust ventilation or use a P100 respirator if welding galvanized or coated materials.
• Eye and Face Protection: Wear an auto-darkening welding helmet with the correct shade setting (typically 10–13) and ensure the clear cover lens is free of spatter.
• Skin Protection: Wear flame-resistant (FR) cotton or leather welding jackets, leather gloves, and high-top leather boots. Avoid synthetic fabrics that may melt.
• Workspace Safety: Clear the area of flammable liquids, gases, or combustible materials. Verify that a fire extinguisher (Class ABC) is within reach.

2. Equipment Setup and Calibration

• Gas Shielding: Verify the gas cylinder contains 100% Argon or the specified Argon/Helium mix. Open the cylinder valve slowly, then set the flow meter to 15–20 cubic feet per hour (CFH).
• Electrode Preparation: Choose the appropriate tungsten (e.g., 2% Lanthanated for versatility). Grind the tungsten point longitudinally (parallel to the rod) on a dedicated grinder to ensure a consistent arc.
• Machine Configuration: Set the machine to "DCEN" (Direct Current Electrode Negative) for steel/stainless, or "AC" (Alternating Current) for aluminum.
• Polarity and Amperage: Connect the torch to the negative terminal and the work clamp to the positive terminal. Set the amperage based on material thickness (approx. 1 amp per 0.001 inch of material).

3. Material Preparation and Fit-up

• Surface Cleaning: Remove all oils, grease, paint, or mill scale from the weld zone using a dedicated stainless steel wire brush or acetone.
• Joint Alignment: Ensure edges are square or beveled according to the weld procedure specification (WPS). Tack-weld the joint at regular intervals to prevent thermal distortion.
• Gap Management: Maintain a consistent gap (fit-up) to avoid excessive "burn-through" or lack of penetration.

4. Execution of the Weld

• Arc Initiation: Hold the torch at a 75-degree angle. Initiate the arc (lift-start or high-frequency start) without touching the tungsten to the workpiece.
• Puddle Control: Establish a molten weld puddle. Wait until the puddle is uniform before adding filler metal.
• Dipping Technique: Add filler metal at the leading edge of the puddle. Do not push the filler rod into the arc, as this causes contamination.
• Shielding Maintenance: Keep the torch gas cup over the cooling weld bead for several seconds after breaking the arc to prevent oxidation (post-flow).

Pro Tips & Pitfalls

• Pitfall - Tungsten Contamination: If the tungsten touches the filler metal or the puddle, it will become contaminated. You must stop immediately, remove the contaminated portion by grinding, and re-sharpen the tip.
• Pitfall - "Sugaring": On stainless steel, a grey or black, crusty appearance on the backside of the weld indicates oxidation. Always use a backing gas (purging) for critical stainless steel joints.
• Pro Tip - Torch Ergonomics: Practice "dry runs" (without power) to ensure your hand position allows for a full range of motion. Rest your forearm or wrist on the table to stabilize the torch.
• Pro Tip - The "Dab" Rhythm: Focus on a consistent rhythm of "dip-move-pause." Consistency in rhythm results in the classic "stack of dimes" appearance.

Frequently Asked Questions (FAQ)

1. Why is my tungsten turning blue or black after welding? This is typically caused by insufficient post-flow gas. Increase your post-flow setting to ensure the tungsten remains shielded by Argon while it cools down.

2. Should I push or pull the torch? For TIG welding, you should almost always "push" the torch (the cup leading the direction of travel). Pulling the torch can draw atmospheric contaminants into the weld puddle, causing porosity.

3. How do I know if I am using the right tungsten size? Generally, 1/16" tungsten is suitable for up to 100 amps, 3/32" for 100–200 amps, and 1/8" for over 200 amps. Using too small a tungsten for high amperage will cause it to melt and ball up.