What is the minimum value rule for impact testing according to API 650?

• A. No specimen can be above the minimum value
• B. No specimen can be less than 2/3 of the specified minimum value
• C. No more than one specimen can comply with the minimum value
• D. All specimens must exceed the specified minimum value

Answer: (B)

The minimum value rule for impact testing according to API 650 specifies that no specimen can be less than two-thirds of the specified minimum value. This rule is in place to ensure that the materials used in the construction of welded tanks possess adequate toughness to withstand impact forces, particularly in low-temperature conditions. The intent is to ensure that even if some specimens have variations in their properties, a minimum threshold of toughness is maintained to avoid brittle failure of the material.

This approach provides a reasonable compromise in allowing some variability in test results while still managing safety and performance requirements. Specimens with impact values below this threshold may indicate compromised material integrity, which can lead to failures in tank operations. Thus, ensuring that all test results are at least at this level helps to establish a safety margin in the material properties used in tank construction.