When rods come out of the holding oven at 250 degrees, how long can they be exposed to air?

The correct duration of exposure to air for rods that have been heated to 250 degrees Fahrenheit is crucial for ensuring that the rods maintain their metallurgical properties. When it comes to high-strength structural steels, specific time limits are set to prevent issues like moisture absorption or oxidation, which can adversely affect the rods' performance.

For rods rated at 70 KSI, the standard allows for an exposure time of up to 4 hours. This longer duration is possible because these rods generally have a lower strength and are more forgiving in terms of changes in properties due to environmental exposure. The exposure time diminishes for higher strength materials, as they are more sensitive to these changes.

In the context of the other options, while higher strength materials such as 80 KSI, 90 KSI, and 100 KSI rods can be exposed to air, their permissible times are much shorter due to their susceptibility to losing their desired characteristics when subjected to the same conditions. However, the option indicating 4 hours for 70 KSI rods is aligned with the guidelines in the Structural Welding Code, making it the correct response.