Building a CUI inspection program: a checklist

Most CUI programs fail in one of two ways. Either they are turnaround lists, where insulation gets removed wherever scaffolding happens to be, or they are spreadsheets that rank everything and inspect nothing. The checklist below is meant to keep a program between those two failure modes. Each step names its inputs, its output and the question it answers.

1. Inventory the insulated assets

Question: what do we own that can suffer CUI?

• List every insulated or fireproofed circuit, vessel, exchanger and tank in scope, with a stable identifier that matches the piping isometrics and the maintenance system.
• Record for each: material, design and operating temperature, cycling or intermittent service, insulation material and thickness, jacketing type, coating under insulation and its date, environment (marine, cooling tower, deluge, industrial), and the count of supports, penetrations and low points where practical.
• Capture the inspection and repair history: date, method, locations, readings, findings, and what was repaired.
• Flag insulation that serves no process or personnel-protection purpose as a removal candidate. The cheapest CUI inspection is on a line that no longer has insulation.

Output: a circuit register. Most of it already exists in isometrics, the equipment database and old inspection reports; the work is consolidation. If the history is in PDFs, see turning inspection reports into data.

2. Screen for susceptibility

Question: which items can be set aside, and which need a closer look?

• Apply the temperature guidance in API RP 583: carbon steel roughly −12 °C to 175 °C, austenitic stainless roughly 50 °C to 175 °C for chloride cracking. Items steadily outside these bands are low susceptibility unless they cycle through them.
• Note the accelerating conditions: absorbent insulation, no or aged coating, marine or cooling-tower exposure, intermittent service, complex geometry, visible jacketing damage.
• Do the walk-down. External visual inspection of the insulation system is required by the inspection codes anyway, and it supplies the condition field.

Output: every circuit tagged as low, medium or high susceptibility, with the reasons recorded.

3. Rank, then backtest

Question: in what order should we spend the inspection budget?

• Score the medium and high circuits on the factors from step 1 and 2, using a consistent scale. API RP 581's CUI damage factor is the formal version; a weighted score is the practical one.
• Decide whether to weight likelihood by consequence (fluid hazard, criticality, cost of an outage) or to rank likelihood alone and apply consequence as a filter.
• Backtest: hide the findings from the last campaign, rank blind, and compare how quickly the ranking reaches the known findings versus the order you would otherwise use. Adjust weights only if the plant's own findings justify it.

Output: a ranked list with the drivers shown per circuit, and a gain chart or equivalent showing the backtest. See risk-based inspection for CUI and the workbench demo.

4. Plan the inspection by method

Question: what will we do at each circuit, and where on it?

• Match method to circuit: pulsed eddy current for insulated carbon steel runs, profile radiography for small bore and supports, guided wave for long inaccessible runs, insulation removal and UT for quantification and for stainless steel. The trade-offs are in CUI inspection methods.
• Name the locations: supports, low points, dead legs, penetrations, terminations. A plan that says "PEC circuit 14" is not a plan; "PEC the twelve supports and two low points on circuit 14, window the lowest reading" is.
• Set follow-up rules in advance: below what reading do we strip, and who decides on repair.
• Arrange access, permits and reinsulation resources at the same time as the NDE crew. Open windows that wait weeks for a weather seal create the next CUI site.

Output: a work list per circuit with method, locations, thresholds and access, sequenced by rank.

5. Execute and record

Question: what did we find, exactly where?

• Record every reading against the circuit identifier and a fixed datum so the next campaign can return to the same point, not just the same line.
• Capture the condition of the coating and the insulation at every window, not only the wall reading. These update the susceptibility fields for the next ranking.
• Photograph before and after reinsulation. Note the seal used.
• Keep screening readings and measurements in separate fields. A PEC percentage and a UT thickness are different kinds of evidence and are graded differently for inspection effectiveness.

Output: structured findings that feed steps 6 and 7, not a folder of PDFs.

6. Evaluate and repair

Question: is the item fit for service, and what do we fix?

• Compare measured wall to the required thickness and remaining corrosion allowance; escalate to a fitness-for-service assessment where loss is significant.
• Specify repairs to the standard the program has adopted: surface preparation, coating system for the operating temperature, insulation material, jacketing and sealing, per AMPP SP0198 and the owner's specification.
• Fix the cause where one is visible: the leaking trap, the upward-facing seam, the missing drip ring.

Output: repair orders and an updated remaining-life estimate per item.

7. Re-rank and review

Question: did the program work, and what changes next time?

• Feed the new findings, coating conditions and repairs back into the register and re-run the ranking. Circuits that were opened and repaired move down; circuits that were screened low move up in confidence but not in rank.
• Rerun the backtest with the new campaign as the held-out set. This is the program's own scorecard.
• Review the method mix: if every low PEC reading turned out to be sound on stripping, the threshold is too conservative; if a leak occurred on a circuit ranked low, find which field was wrong.
• Set the next campaign's scope and budget from the ranking, and document the review for the inspection codes' program requirements.

Output: a program that gets better each cycle, and evidence that it does.

The one-page version

References

• API RP 583, Corrosion Under Insulation and Fireproofing, program elements. Our summary.
• API RP 580 and API RP 581 for the risk-based framework and the CUI damage factor.
• API 570 and API 510 for external inspection intervals and the program records the codes expect.
• AMPP SP0198 for coating and insulation system repair specifications.