There is a complex network of ~800 miles (1280 km) of above ground pipelines in one of the largest oil
fields on the North Slope of Alaska. This infrastructure has been in operation for nearly three decades,
transporting crude oil, water and gas. The vast majority of the piping network is insulated with
polyurethane foam over bare steel, and is therefore susceptible to corrosion under insulation (CUI).
The sheer magnitude of the number of locations susceptible to CUI poses integrity management
challenges that call for a better understanding of damage onset and progression rates as well as
underlying causes. Radiographic testing, visual inspection, and refurbishment data were analyzed for
~73 miles (117 km) of pipelines where complete external corrosion inspection histories were available.
The analysis showed that the accumulated damage distribution over time could be fit to Weibull curves,
which appear to correlate with the total number of CUI repairs and refurbishments that need to be done
each year. The Weibull curves generated were employed to predict the number of CUI susceptible
locations that would need repair or refurbishment each year for all 800 miles of pipelines in the field.
The model can be further used as input to risk assessments to support maintenance strategies, and as
background rationale for budgeting and manpower optimization for inspection, repair and refurbishment
activities.
Key Words: corrosion under insulation, CUI, pipeline, Weibull statistical analysis