Pipeline Inspections

The Prediction of Pipeline Condition:

The AESL Condition Assessment Process uses inspection data from the smartCAT™ or the smartCAT™ 360 magnetic inspection tools, and from spot readings using a commercial ultrasonic tool, to define the potential for the leakage and structural failure in longer lengths of the pipeline:

Pipeline leakage is predicted based on the potential growth of individual corrosion pits until they are through wall.

Pipeline structural performance predictions are based on the measured corrosion levels and the applied loading regimes, considering the following:

Leakage Prediction:

The potential for leakage from the un-inspected lengths of pipeline, due to through wall pitting, is based on the identified pitting corrosion patterns and range of pit depths in the inspected length(s). The process predicts:

• The defect depth range including the maximum defect depth, and numbers of defects of each depth, along the un-inspected pipeline section
• The maximum corrosion rate based on the measured original pipe wall thickness, the deepest predicted corrosion pit and the pipes age
• The time to through wall pitting corrosion and the growth in numbers of such corrosion pits with time

Where prediction is considered statistically valid, predictions of the current likelihood of pipeline leakage, due to through wall corrosion, and of the future increase in patterns of such leakage as corrosion progresses are provided.

These leakage predictions are based on the standard AESL pipeline inspection process outputs. However, the statistically predictions are based on analysis of the corrosion pits within a defined grid pattern. The number of corrosion pits identified in the inspected 1m lengths of the pipeline determines whether statistical prediction is possible. If appropriate, additional inspection sites to obtain the necessary amount of inspection data can be agreed with the customer.

Structural Performance Predictions

Structural performance predictions are based on an analysis of the pipeline deterioration and the maximum applied loading regimes. The structural performance predictions consider:

Surface loading for crushing or bending failure (overburden, traffic etc)

Fracture risk for grey iron pipe based on initiation from a single pitting defect

Failure risk for ductile iron and steel pipe based on estimated membrane and bending stresses

Predictions of the time for these failure modes to occur based on estimated corrosion rates

The likelihood of structural failure of the pipeline due to corrosion deterioration is calculated using standard and AESL developed stress analysis modelling techniques.