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Source |
Corrosion Rate or Degree of Corrosion |
Remaining Life or Fitness for Service |
Application |
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API 570 |
Long-term (between last and initial inspections): |
(use corrosion rate resulting in shortest remaining life) |
Piping |
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Short-term (between last and previous inspections): |
Piping and Vessels |
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NBIC – 23 |
a) calculated from data collected by owner or user on vessels in the same or similar service b) owner or user’s experience or from published data c) determinations made after 1000 hours of service |
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API 510 |
See API RP 579 for fitness for service determinations |
Vessels |
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API 653 |
t1 = the lowest average thickness of a profile t2 = the least thickness, in inches, in an area of corrosion, exclusive of pits |
Fit for service if: a) 2 minimum t ≥ t b) 2 .6 minimum t ≥ t (corrosion allowance required for service until next inspection should be added to t minimum) |
Tanks |
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ASME B31.3 |
The selection of material to resist deterioration in service is not within the scope of this Code. |
Piping and Heat Transfer Components |
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ASME B31.5 |
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IIAR 109 |
If the heat exchanger or pressure vessel shows signs of corrosion beyond mild surface corrosion, it should be further inspected for soundness. If corrosion exists on piping, the pipe should be cleaned down to bare metal and painted with a rust preventable paint. (4.3.4)
The badly corroded pipe should be replaced. (4.7.4) |
Piping, Vessels, and Heat Transfer Components |
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IIAR 110 |
Where external corrosion has formed pits or caused a material loss that reduces the thickness of the pressure vessel or shell-and-tube heat exchanger, the inspecting person should measure or cause to be measured the thickness of the remaining metal to determine whether the replacement is necessary…the design records…the design codes…the calculated minimum wall thickness, and the NBIC rules or other appropriate guidance for evaluating corrosion should be considered.
The actual metal thickness should be determined using an appropriate non-destructive testing technique, for example: ultrasonic measurements. (6.4.4.2) |
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t actual = the actual minimum thickness, determined at the time of inspection t minimum = the minimum required thickness for the limiting section or zone |
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Source: IRC Mechanical Integrity Workshop |
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