Inspectioneering Journal

Extending the Life of an Offshore Pipeline

By F Egan at Zadco, D G Jones at PII Pipeline Solutions business of GE Oil & Gas, and J Healy at Macaw Engineering Ltd. This article appears in the September/October 2006 issue of Inspectioneering Journal.
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The Situation

Active corrosion in onshore and offshore pipelines is an increasing problem. Consequently, pipeline operators regularly use intelligent inspection pigs to detect and size corrosion. Inspection data can be combined with probability based “Fitness-For-Purpose” assessment methods, to determine the effect of corrosion on the immediate and future integrity of the pipeline.

  • corrosion inhibition
  • repair
  • de-rating
  • and/or pipeline replacement

A Middle East operator owned an offshore crude oil pipeline, which contained extensive internal corrosion. He wanted to know if the pipeline’s life could be extended.

The Approach

Fully quantitative probabilistic corrosion assessments were conducted in 1995 and 2003 using SORM (second-order reliability method) methods, to provide the operator with the technical basis required to ensure the long-term integrity of the pipeline. The relationships between:

  • probability of failure
  • operating pressure
  • corrosion growth rate
  • number of repairs and
  • safe remaining pipeline life, were investigated, in order to schedule optimally the RBI programme. In 2003, GE used its unique RunComTM (RUN COMparison, which measures corrosion growth from raw MFL data) software to quantify accurately the corrosion growth distribution in the pipeline, enabling accurate stochastic modelling of corrosion growth behaviour. This working relationship has continued with the operator for 15 years over 5 inspections; the most recent of which was in 2003.

The Results & Benefits

It was identified that if the corrosion rate could be limited below a certain value, the operating life of the pipeline could be extended by > 30 years. The cost of corrosion monitoring and control measures to achieve his rate over 30 years was estimated at $60 million. The alternative of pipeline replacement was estimated at $250 million. The detailed assessment confirmed that corrosion control would offer a significant return on investment. Repeat inspections have confirmed both that the improved Corrosion Management Strategy developed by the operator has been effective; and that the predictions from the fully quantitative assessment were accurate.

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