16 Inch Williams Gas Pipeline Inspected for SCC Using PII’s New Ultrasonic Tool

The in-line-Inspection of Williams’ Gas West Pipeline in September 2001 was successfully completed using the newly developed 16” UltraScan® CD tool of GE PII Pipeline Solutions. The particular pipeline section inspected was known to be affected by Stress Corrosion Cracking (SCC). The inspection was carried out using the liquid batching technique developed by PII Pipeline Solutions. A special launcher and receiver barrel was designed to enable the handling of a series of three batching pigs in front of and two behind the inspection tool. A manifold of “kicker lines” was mounted to the barrel to launch the batching pigs and the inspection tool. The main benefits of this new design were minimizing operational downtime, ensuring complete air/natural gas displacement from the launcher, and providing for a smoother launch procedure. Due to the large elevation changes within the pipeline section, a key concern was maintaining pig velocity within 1m/s for adequate data resolution. Rather than rely on a general “rule of thumb”, a transient analysis was performed to define a range of possible batch sizes and better understand the expected pressure gradients while pumping the water slug. Based on actual data collected during this successful run, the transient model will be refined to better handle friction effects between the sealing cups and disks in future batch inspection runs. The data analysis stage for large crack features is completed and full analysis for small defects is ongoing. Analysis and excavation results are discussed in the paper. Results from this inspection are expected to considerably extend the understanding of crack formation in this pipeline and will be used to help establish an overall integrity management plan for the pipeline.