Where should an inspector consider getting thickness readings if a vessel lacks a thickness history?

When an inspector is faced with a pressure vessel that lacks a thickness history, it's crucial to obtain a comprehensive understanding of its current condition. Taking thickness readings at one location only, such as at the weld joints, would not provide a complete picture of the vessel's integrity. Similarly, focusing only on the most corroded areas or just the top and bottom of the vessel would ignore critical regions where degradation might occur, potentially leading to missed issues.

The approach of measuring thickness at one on the four quadrants of each shell ring and the four quadrants of both heads is the most thorough and systematic method. This strategy ensures that the inspector captures variations in material thickness across different sections of the vessel. By sampling in this way, the inspector can identify trends, areas of concern, and the overall condition of the vessel more accurately. It provides a more representative assessment of the vessel's integrity, helping to inform maintenance decisions and safety evaluations.