Cased Crossings and Guided Wave Ultrasonics
When transmission pipelines traverse through areas of high consequence to people, property or the environment, they are required to follow PHMSA's Integrity Management (IM) requirements. An IM approach identifies specific threats to the pipeline that operators must address through a plan to prevent, detect, characterize and remediate them.
In some cases, pipelines are cased when they cross under rivers, roads and rail road right of ways. When these cased crossings are located in a High Consequence Area (HCA), they fall under the IM requirements and must be in compliance with prescribed milestones. With best estimates, there are thousands of cased crossings nationwide and hundreds if not thousands located in HCAs.
Cased crossings are essentially a pipe within a pipe and utilize centralizers for maintaining an equal axial distance between the carrier pipe and the casing. Some are filled with wax, open to the atmosphere or sealed. Cased crossings can range from approximately 20 to over 300 feet long. These varying scenarios combined with the fact that the line cannot be dug up without major disruption to other infrastructure or public services labels them as tough to inspect areas and pose unique challenges for pipeline operators.
Historically, in-line inspection, pressure testing and Direct Assessment (DA) provided the only assessment options for the pipeline industry. But in some cases, obstructions in the pipeline, the expense of pressure testing, the revenue loss from downtime and the uncertainty of risk and data within the DA process detract and remove these as viable assessment options. In these situations, other technologies or assessment options have been proposed to PHMSA and reviewed case by case.
PHMSA, the pipeline industry and Standards Developing Organizations (SDO) are collaborating to create additional assessment options for cased crossings. A comprehensive program to address the integrity management of cased crossings is well underway involving collaborative research, technology demonstrations, consultation with subject matter experts, the integration of knowledge with SDOs and the culmination of all efforts into a focused integrity management process.
This web page documents the relevant collaboration and is a resource for all affected stakeholders.