Which statement correctly defines the maximum thickness inspection interval for Class 2 & 3 piping?

Which statement correctly defines the maximum thickness inspection interval for Class 2 & 3 piping?

• A. The greater of 10 years or half-life of the pipe.
• B. The lesser of 12 years or half-life of the pipe.
• C. Exactly 10 years for all pipes.
• D. The lesser of 10 years or half-life of the pipe.

Answer: (D)

The key idea is setting a thickness inspection interval based on how quickly the pipe walls are thinning. For Class 2 & 3 piping, the maximum interval is the lesser of 10 years or the pipe’s half-life. The half-life here is the time required for the remaining wall thickness to drop to half at the current or projected corrosion rate. If the corrosion rate is fast, the half-life is short, so you must inspect sooner than 10 years. If thinning is slow and the half-life exceeds 10 years, you’re still limited to a 10-year cap. The other options either allow longer intervals than are safe or ignore the corrosion-rate-based limit, which is why they’re not correct.

The key idea is setting a thickness inspection interval based on how quickly the pipe walls are thinning. For Class 2 & 3 piping, the maximum interval is the lesser of 10 years or the pipe’s half-life. The half-life here is the time required for the remaining wall thickness to drop to half at the current or projected corrosion rate. If the corrosion rate is fast, the half-life is short, so you must inspect sooner than 10 years. If thinning is slow and the half-life exceeds 10 years, you’re still limited to a 10-year cap. The other options either allow longer intervals than are safe or ignore the corrosion-rate-based limit, which is why they’re not correct.