April 2023, Vol. 250, No. 4

Tech Notes

Tech Notes: Unpiggable In-Line Inspection Completed in South America

Special to P&GJ 

(P&GJ) — A team of Dexon pipeline engineers recently completed the inspection of a 20-mile (32-km), 3-inch diameter unpiggable or “challenging” underground petrochemical distribution pipeline, running from an onshore processing facility to a port on the South American coast.

Pipeline engineer Panuset Roopsang and a team from Dexon’s inspection department, with a client following the inspection.

This was the first inspection for this pipeline in its 30-year life due to the challenging nature of the inspection. 

The small diameter of the pipeline meant that specialized tool development, modification, and testing were required at Dexon’s headquarters in Thailand prior to the inspection, with onsite client verification performed in early December of 2022. 

The Challenge 

  • Inspection of a long-range 20-mile (32-km) distribution pipeline (A typical 3-inch transfer lines run for only a few hundred meters in a single plant) 
  • Pipeline characteristics such as weld penetration can cause significant internal diameter restrictions in small-diameter pipelines 
  • A lack of previous inspection data with this being the first inspection for this pipeline 
  • Online inspection 

The small diameter of the pipeline, paired with the long inspection length of  20 miles (32 km), made this inspection challenging. Typical 3-inch transfer pipelines run for a few hundred (200 to 400) meters within a single plant making this run 106 times longer usual. While weld penetration and other characteristics in small-diameter pipelines can cause significant reductions in the pipeline’s internal diameter.  

Limited space inside the tool bodies caused by the small diameter required customized design, modification and testing of the tool prior to the inspection. Providing sufficient battery life and data storage to complete the inspection.  

The lack of an inspection history causing uncertainty around the geometric condition of the pipeline in underground sections which could possibly lead to a stall. The client required the inspection to be completed online reducing the impact on operations. 


  • Customized design and modification of the existing 3-inch small diameter UT-MC fleet. 
  • Customization of onsite test loop configurations to replicate inspection conditions. 
  • Extensive long-range durability testing at the onsite test yard. 
  • Onsite client inspection data verification.  
  • Comprehensive cleaning and gauging to adequately gauge the geometric condition of the pipeline prior to inspection.  

The pig traveling at approximately 1 m/s over the distance, for a total inspection time of nine hours from launching to receiving. Dexon Mechanical Solutions (DMS) performed alterations to the onsite test loop configurations to replicate inspection conditions and allow for extensive long-range durability testing prior to the inspection.  

Onsite client inspection data verification was performed in early December of 2022 with a team of pipeline operators visiting Dexon’s headquarters in Thailand. 

Cleaning and gauging were performed onsite to adequately determine the geometric condition of the pipeline to avoid a stall in the line. 

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