The purpose of RBI is to identify susceptible pressure vessels, piping and fireproofed structural supports subject to CUI/CUF, to prioritize inspections, and to develop an inspection plan to reduce risk.
1. The information needed to assess the likelihood of failure due to CUI or CUF damage includes, but is not limited to:
• Specific site environment
• Material of construction
• Age of component
• Operating process temperature
• Exposure to intermittent/cyclic service
• Areas with missing insulation
• Age of insulation/fireproofing
• Type of coating present, if any
• Age of coating
• Presence and condition of steam tracing
This data can be obtained from a variety of sources, and can include the original engineering records, Management of Change (MOC) database, maintenance work order records, and inspection records. Other data, which pertains to the physical condition of the component, can be obtained from a field inspection. These inspections can be incorporated into the external inspection programs, or may be part of a special emphasis CUI inspection project.
2. Prior to conducting the assessment, the atmospheric environment of the area being assessed within the plant needs to be classified. Examples of atmospheric environment descriptors included in API RP 581 are arid/dry area, temperate area, severe area, arid marine/cooling tower drift area.
3. Due to the highly localized nature of damage, CUI and CUF assessments lend themselves to a qualitative assessment approach to assess the likelihood of failure.
3.1 The owner/user may modify (i.e. add or eliminate) the number of parameters, change the description of individual parameter categories, modify the value of individual parameter ratings, increase or decrease the minimum or maximum range of individual parameters, or the total number of likelihood rating categories to address company or site-specific factors.
4. The owner/ user should consider the differences between potential failure modes for each of the damage mechanisms when assessing consequence. Namely,
• Corrosion hole from CUI (most frequently a small leak)
• Cracking for ECSCC of austenitic/duplex stainless steels (most frequently a small leak)
• Rupture/Structural instability (rare event)
It should be recognized that while many CUI leaks occur from smaller pits, a number of CUI loss of integrity events have occurred as a result of larger locally thinned areas. The owner/user should assess the consequence of both types of risks in the risk assessment process.
5. Consequence assessment should conform to the documented site consequence assessment process. Guidance on RBI consequence assessment can be found in API RP 580 and 581. Though CUI damage is most often likely to produce an equipment reliability issue, in rare cases, safety and environmental issues can arise.
1. The information needed to assess the likelihood of failure due to CUI or CUF damage includes, but is not limited to:
• Specific site environment
• Material of construction
• Age of component
• Operating process temperature
• Exposure to intermittent/cyclic service
• Areas with missing insulation
• Age of insulation/fireproofing
• Type of coating present, if any
• Age of coating
• Presence and condition of steam tracing
This data can be obtained from a variety of sources, and can include the original engineering records, Management of Change (MOC) database, maintenance work order records, and inspection records. Other data, which pertains to the physical condition of the component, can be obtained from a field inspection. These inspections can be incorporated into the external inspection programs, or may be part of a special emphasis CUI inspection project.
2. Prior to conducting the assessment, the atmospheric environment of the area being assessed within the plant needs to be classified. Examples of atmospheric environment descriptors included in API RP 581 are arid/dry area, temperate area, severe area, arid marine/cooling tower drift area.
3. Due to the highly localized nature of damage, CUI and CUF assessments lend themselves to a qualitative assessment approach to assess the likelihood of failure.
3.1 The owner/user may modify (i.e. add or eliminate) the number of parameters, change the description of individual parameter categories, modify the value of individual parameter ratings, increase or decrease the minimum or maximum range of individual parameters, or the total number of likelihood rating categories to address company or site-specific factors.
4. The owner/ user should consider the differences between potential failure modes for each of the damage mechanisms when assessing consequence. Namely,
• Corrosion hole from CUI (most frequently a small leak)
• Cracking for ECSCC of austenitic/duplex stainless steels (most frequently a small leak)
• Rupture/Structural instability (rare event)
It should be recognized that while many CUI leaks occur from smaller pits, a number of CUI loss of integrity events have occurred as a result of larger locally thinned areas. The owner/user should assess the consequence of both types of risks in the risk assessment process.
5. Consequence assessment should conform to the documented site consequence assessment process. Guidance on RBI consequence assessment can be found in API RP 580 and 581. Though CUI damage is most often likely to produce an equipment reliability issue, in rare cases, safety and environmental issues can arise.
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