In a vessel that moved from hydrocarbon service to chemical service, which thickness reading should be considered the "Initial Thickness" for corrosion rate calculation?

In a vessel that moved from hydrocarbon service to chemical service, which thickness reading should be considered the "Initial Thickness" for corrosion rate calculation?

• A. 1986 reading
• B. 2005 reading
• C. Reading to use is selected by Corrosion Specialist
• D. Reading to use is selected by the Inspector

Answer: (B)

In a scenario where a pressure vessel transitions from hydrocarbon service to chemical service, the "Initial Thickness" for calculating the corrosion rate is typically derived from the most recent thickness reading before the service change. This is because the condition of the vessel material is essential for assessing its integrity under the new service conditions. In this context, the 2005 reading would be deemed most appropriate since it is likely the last documented measurement before this transition occurred. This new service may expose the vessel to different corrosive environments, and understanding the thickness from the last known state helps in evaluating how much material may have been lost due to corrosion since then and assists in establishing a reliable corrosion rate. Choosing an older reading, such as from 1986, may not accurately reflect the vessel's condition as it neglects any changes that occurred during the intervening years in hydrocarbon service. Moreover, while the input from corrosion specialists or inspectors is valuable for contextual understanding and risk analysis, the most recent measurement prior to the service change serves as the best baseline for corrosion rate calculations.

In a scenario where a pressure vessel transitions from hydrocarbon service to chemical service, the "Initial Thickness" for calculating the corrosion rate is typically derived from the most recent thickness reading before the service change. This is because the condition of the vessel material is essential for assessing its integrity under the new service conditions.

In this context, the 2005 reading would be deemed most appropriate since it is likely the last documented measurement before this transition occurred. This new service may expose the vessel to different corrosive environments, and understanding the thickness from the last known state helps in evaluating how much material may have been lost due to corrosion since then and assists in establishing a reliable corrosion rate.

Choosing an older reading, such as from 1986, may not accurately reflect the vessel's condition as it neglects any changes that occurred during the intervening years in hydrocarbon service. Moreover, while the input from corrosion specialists or inspectors is valuable for contextual understanding and risk analysis, the most recent measurement prior to the service change serves as the best baseline for corrosion rate calculations.