A significant proportion of North America's natural gas transmission network consists of vintage low-frequency electric resistance welded (LF-ERW) pipe. These assets can be susceptible to longitudinal seam threats, including selective seam weld corrosion and lack of fusion. Conventional axial magnetic flux leakage (MFL-A) may not provide a strong response to such features, while traditional free-swimming inline inspection can be impractical in pipelines with limited access, low flow, restrictive geometry, or no permanent launcher and receiver.

This white paper presents a 2025 inspection completed by Pacific Gas and Electric Company and Intero Integrity Services on a 6,400 ft segment of 10 in. LF-ERW natural gas transmission pipeline installed in 1966. The team deployed Intero's tetherless, self-propelled Pipe Explorer robotic platform through temporary hot-tap fittings without interrupting normal gas service. The robot collected axial MFL, circumferential MFL (MFL-C), laser deformation, and internal video data.

A newly developed segmented MFL-C seam sensor was aligned to the longitudinal seam of each of the segment's 146 pipe spools. The inspection reported 30 longitudinal indications, including four anomalies that met the reporting and sizing threshold. The reportable features produced clear MFL-C responses but were not visible as equivalent anomalies in the axial dataset. By combining controlled robotic navigation with complementary sensing technologies, the project delivered a comprehensive integrity dataset for a challenging-to-inspect pipeline and expanded the options available for evidence-based management of seam-related risk in aging ERW assets.

Download the white paper to learn more.