During an internal inspection of a large vessel, the inspector discovers a significant coke deposit. What is the next appropriate action?

Choosing to determine if the base metal under the coke deposit is corroding reflects an important aspect of pressure vessel inspection and integrity management. When significant coke deposits are found, it is critical to assess the condition of the underlying material. This is because the presence of deposits can often hide corrosion or other forms of degradation that may compromise the vessel's integrity.

Measuring the deposit thickness could provide some information about the extent of the buildup, but it does not directly address the condition of the base metal beneath. Simply cleaning the deposit may not be advisable without understanding the condition of the metal underneath. Ignoring the deposit, even if it appears stable, poses a risk, as any undetected corrosion could lead to failure under operating conditions.

Hence, the focus on evaluating the base metal ensures that the inspector is considering both the immediate safety and long-term reliability of the pressure vessel. This assessment is crucial for making informed decisions about maintenance or repairs that may be necessary to ensure continued safe operation.