RBI Program Reducing Turnaround Inspection Scope at a Refinery

Executive Summary

A refinery operating a time-based equipment inspection program required a transition to a risk-based approach, as escalating turnaround scope and cost had outpaced any corresponding safety justification for the equipment being inspected. The facility's engineering team suspected — correctly, as the RBI assessment confirmed — that inspection effort was not well correlated with actual equipment risk, with some genuinely high-risk items under-inspected while some low-risk items consumed disproportionate turnaround time. This representative example illustrates API 580/581-aligned RBI methodology and findings typical of refineries transitioning from time-based to risk-based inspection programs.

Facility Background

The refinery's static equipment population covered several hundred pressure vessels, piping circuits, storage tanks, and heat exchangers across crude processing, hydroprocessing, and utility systems, with an inspection program historically based on largely uniform, code-minimum time intervals rather than equipment-specific risk. Turnaround scope had grown over successive cycles as more equipment reached inspection due-dates simultaneously under the time-based schedule, without a corresponding risk-based justification for the resources being allocated to each item.

Hazard Profile

• —Active damage mechanisms varying significantly across the equipment population, including sulfidation corrosion in high-temperature crude units, hydrogen-related cracking in hydroprocessing equipment, and general corrosion in utility and cooling water systems
• —Consequence of failure ranging from minor utility system leaks to major hydrocarbon loss-of-containment events in high-pressure, high-temperature process equipment
• —Equipment age variation across the population, with some assets significantly exceeding the age at which original design-basis corrosion allowance assumptions remain reliable
• —Turnaround scheduling constraints creating pressure to defer or compress inspection scope without a risk basis for which deferrals were actually acceptable

Study Methodology

1. 1.Equipment population data consolidation, compiling process conditions, materials of construction, and inspection history for over 400 equipment items into the RBI assessment basis
2. 2.Probability of failure assessment per API 581 methodology, evaluating active damage mechanisms for each equipment item based on process conditions and prior inspection findings
3. 3.Consequence of failure assessment considering safety, environmental, and financial impact of a credible loss of containment at each equipment item, using simplified consequence modelling calibrated to equipment type and location
4. 4.Risk ranking of the full equipment population, identifying the highest-risk items disproportionately driving overall facility risk
5. 5.Inspection plan optimisation, adjusting technique and interval per equipment item based on its calculated risk ranking rather than a uniform time-based default
6. 6.Turnaround scope recommendation, translating the risk-based inspection plan into a prioritised turnaround work list

Key Findings

• —A small subset of equipment, roughly 8% of the population, accounted for a disproportionate share of total calculated facility risk, driven primarily by active high-temperature sulfidation and hydrogen-cracking mechanisms
• —A larger subset of equipment, subject to benign service conditions with well-controlled damage mechanisms, was being inspected at a frequency the calculated risk did not justify
• —Several equipment items had inspection history data insufficient to support a fully quantitative probability-of-failure calculation, requiring a conservative default assumption pending additional inspection data
• —Consequence of failure rankings correlated strongly with equipment size and proximity to occupied control areas, consistent with expectations but not previously reflected in the facility's inspection prioritisation

Risk Reduction Measures

• —Inspection frequency increased and technique upgraded (including advanced non-destructive testing methods) for the highest-risk 8% of the equipment population
• —Inspection interval extended for the lower-risk equipment subset shown to carry risk well within acceptable bounds, reducing next turnaround scope by 22% on these items
• —A data-gathering inspection scheduled for equipment items with insufficient historical data, to support a fully quantitative risk ranking at the next assessment cycle
• —RBI program formally adopted as a living system, with risk rankings scheduled for periodic update as new inspection data becomes available

Lessons Learned

Technical Takeaways

• —Base inspection interval and technique decisions on calculated risk ranking, not uniform time-based defaults
• —Expect a small fraction of equipment to account for a disproportionate share of total facility risk, and prioritise accordingly
• —Schedule targeted data-gathering inspections for equipment lacking sufficient history for quantitative risk ranking
• —Treat RBI as a living program requiring periodic risk ranking updates, not a one-time reprioritisation