For a fillet weld 4 inches long in a statically loaded non-tubular joint under AWS D1.1, which condition of piping porosity is unacceptable?

In the context of AWS D1.1, piping porosity refers to the presence of small voids or gas pockets within a weld that can compromise its integrity. The acceptable limits for porosity in welded joints are specifically defined to maintain the strength and reliability of the weld.

The correct choice indicates that the unacceptable condition is having five piping pores that sum to a diameter equal to 1/2 inch. This is considered unacceptable because the code stipulates limits on the size and number of pores to ensure that the weld can perform effectively under load.

When assessing porosity, the number of individual defects and their combined dimensions are critical. While a single large pore or several smaller pores can be evaluated, the cumulative effect of porosity can lead to significant weakness in the weld. In this case, five pores summing to 1/2 inch exceeds the allowable number and size, as it indicates a higher density of defects which could potentially lead to failure under load conditions.

For the other options, they either contain fewer pores or smaller total diameters that might fall within acceptable limits, making them more permissible. Therefore, option C is the only one that reflects a condition that is deemed unacceptable based on the standards set by AWS D1.1.