If welding at 150 A, approximately how long should the post-flow last?

• A. About 15 seconds
• B. About 150 seconds
• C. About 1.5 seconds
• D. About 12 seconds

Answer: (A)

Post-flow is the time the shielding gas keeps flowing after the weld arc stops to protect the hot weld and prevent oxidation as it cools. The amount of post-flow you need increases with amperage because higher heat means the weld and heat-affected zone stay hot longer and are more vulnerable to air contamination. A common rule-of-thumb is about one second of post-flow for every ten amperes (roughly 0.1 seconds per amp). At 150 A, that works out to about 15 seconds. Too short a post-flow risks oxidation of the weld, while going much longer is usually unnecessary. So, aim around 15 seconds after stopping the arc for this current level.