If the current vessel wall thickness is 0.500" and the minimum required shell thickness is 0.400", what is the maximum pit depth allowed?

If the current vessel wall thickness is 0.500" and the minimum required shell thickness is 0.400", what is the maximum pit depth allowed?

• A. Less than 0.100"
• B. Less than 0.200"
• C. Less than 0.250"
• D. Less than 0.300"

Answer: (D)

To determine the maximum allowable pit depth, it's important to consider the difference between the current wall thickness and the minimum required thickness of the pressure vessel. The current vessel wall thickness is 0.500 inches, while the minimum required shell thickness is 0.400 inches. First, we calculate the available thickness that can be lost due to pitting. This is done by subtracting the minimum required thickness from the current wall thickness: 0.500 inches (current thickness) - 0.400 inches (minimum thickness) = 0.100 inches. This result shows that the maximum total loss of material in the vessel wall—due to corrosion or other factors—cannot exceed 0.100 inches to ensure the vessel still meets the required minimum thickness for safe operation. However, the maximum pit depth must also take into account that pitting damage can create localized areas of reduced thickness. To ensure that the structural integrity and pressure containment of the vessel are maintained, engineering standards typically allow for a pit depth that is less than the total allowable thickness loss considered safe in service. In many guidelines, such as those outlined by API RP 577 and other relevant codes, a common rule of thumb is that the maximum pit depth should be less than half

To determine the maximum allowable pit depth, it's important to consider the difference between the current wall thickness and the minimum required thickness of the pressure vessel. The current vessel wall thickness is 0.500 inches, while the minimum required shell thickness is 0.400 inches.

First, we calculate the available thickness that can be lost due to pitting. This is done by subtracting the minimum required thickness from the current wall thickness:

0.500 inches (current thickness) - 0.400 inches (minimum thickness) = 0.100 inches.

This result shows that the maximum total loss of material in the vessel wall—due to corrosion or other factors—cannot exceed 0.100 inches to ensure the vessel still meets the required minimum thickness for safe operation.

However, the maximum pit depth must also take into account that pitting damage can create localized areas of reduced thickness. To ensure that the structural integrity and pressure containment of the vessel are maintained, engineering standards typically allow for a pit depth that is less than the total allowable thickness loss considered safe in service.

In many guidelines, such as those outlined by API RP 577 and other relevant codes, a common rule of thumb is that the maximum pit depth should be less than half