Custom caliper solution helps client locate diameter change without excavation

Challenge

A client needed to inspect a 3,000‑ft section of 6‑in. gas pipeline that included an undocumented 4‑in. sub‑segment. The line crossed an environmentally sensitive corridor and an active railroad, making excavation and exploratory digs impractical and high‑risk. The client required a safe, nonintrusive method to confirm the reduced diameter and verify tool passage before running an inspection tool.

Solution

Paxon and a technical collaborator designed a dummy pig and a custom 6‑in. × 4‑in. caliper tool capable of navigating both diameters and 1D bends via wireline. Paxon depressurized a 300‑ft segment to 0 psi to enable a tethered inspection. Initial tow‑pig attempts could not pass the tight diameter transition. To overcome this, Paxon and the collaborator partnered with a parachute‑pig manufacturer to develop an alternative pull method. After overnight delivery, Paxon executed a staged approach:

A parachute pig pulled 1/8-in. rope through the full segment
The rope was used to pull mule tape back through
The mule tape was connected to the wireline to pull the dummy tool and confirm clearance
After confirming the package could pass, Paxon completed the full caliper run without tool damage

Result

Paxon safely identified the location of the reduced‑diameter section and delivered a complete geometry inspection and XYZ mapping of the 3,000‑ft line for integrity and GIS records. The nonintrusive method allowed the client to avoid excavation, protect the environmentally sensitive corridor and railroad crossing, and confirm the pipeline’s configuration with confidence.

Key outcomes

Located undocumented diameter change without excavation
Custom 6-in. × 4-in. caliper tool designed for the specific challenge
Complete geometry inspection and XYZ mapping delivered
Environmentally sensitive corridor and railroad crossing protected
Zero excavation or exploratory digs required
Pipeline configuration confirmed with full integrity records
Innovative parachute-pig pull method developed on-site
GIS-ready data delivered for long-term asset documentation

Paxon services applied

Integrity management

Custom caliper tool design, geometry inspection, XYZ mapping, and asset documentation for pipeline integrity records.

Construction and inspection management

Field oversight for depressurization, tethered tool runs, and safe execution in an environmentally sensitive corridor.

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Integrity management