Minimum no. of tubes?

[ww2i]

What is the minimum number of tubes to be inspected for a heat exchanger when it is made available for inspection?
Is there any criteria available?

[tuan]

There is a criteria mentioned in some of the standard but I do not recall now.
Remember our maintenance colleagues along with inspection make sure of that minimum tubes covered.

[irish]

Minimum tubes to inspect = 10% (if ≤100 tubes) or 5% (if >100 tubes, but ≥10 tubes).
This reference is from ASME PCC-2 Article 312, over an above which you can apply risk based adjustments as per API 572.
Like what we do in critical services (flammable, toxic, or high-pressure systems), 20–30% minimum or even 100% of tubes, depending upon history, and the inspection test results.
No one wants to let the opportunity go wasted, and at the same time, overdoing would give nothing in return.

[neo]

Thanks Irish for this reference.

[ben]

The reference which we have come across most of the times is from API RP 572 which emphasizes risk-based inspection in this case.
The number of tubes inspected should be adjusted based on:

• Service severity (e.g., corrosive fluids, fouling tendency).
  Past inspection history.
  Criticality of the exchanger in the process.

[ww2i]

Thanks. The references especially worked.