The use of class locations is an old approach that addresses the risk posed by gas transmission pipelines by designating the maximum design pressure for a pipeline based on the population of the area through which the pipeline traverses. The Pipeline and Hazardous Materials Safety Administration (PHMSA) is now considering eliminating the class location system and replacing it with an expanded integrity management (IM) approach. 

The PHMSA is soliciting feedback on a lengthy list of issues it will consider before making a rulemaking decision.  Comments must be submitted by September 30, 2013.

Class location

According to the PHMSA, the class location concept pre-dates federal regulation of pipelines.  Class location is determined by counting the number of dwellings within 660 feet of the pipeline for 1 mile (for Classes 1 to 3) or by determining that four-story buildings are prevalent along the pipeline (Class 4).  Design factors used to determine the design pressure for steel pipe and which generally reflect the maximum allowable percentage of the specified minimum yield strength (SMYS) are 0.72 for Class 1; 0.60 for Class 2; 0.50 for Class 3; and 0.40 for Class 4.  Pipelines are designed based on population along their route and thus, class location.

A class location can change as population grows and more people live or work near the pipeline.  When a class location changes, a pipeline operator must either reduce the pipe’s operating pressure to reduce stress levels in the pipe; replace the existing pipe with pipe that has thicker walls or higher yield strength to yield a lower operating stress at the same operating pressure; or, where the class is changing only one class rating, such as from a Class 1 to Class 2 location, conduct a pressure test at a higher pressure.

IM

IM for gas transmission lines uses a different approach to identify areas of higher risk along pipelines.  The term high consequence area (HCA) is used to identify pipelines that are subject to ongoing pipeline integrity assessments.  HCAs are defined by counting the number of dwellings for human occupancy or identified sites where people congregate, such as a hospital or daycare facility, within a calculated circle a pipeline failure could affect.  Operators must periodically inspect the condition of their pipelines in an HCA and remediate any degradation that might affect the pipeline’s integrity.

Safety inspections

The PHMSA notes that while the class location requirements provide an additional safety margin for more densely populated areas, the class location does not address the potential reduction of that safety margin over time due to corrosion or other types of pipe degradation.

“IM requirements and HCA calculations provide additional safety for more densely populated areas because operators are required to conduct periodic inspections of the pipe and because repair timelines are specified for the anomalies identified within an HCA,” states the PHMSA.  “Substituting an IM approach for the use of class locations would allow the operation of the pipeline at higher pressures while conducting integrity inspections and remediation to maintain safety.”

Single design factor

The PHMSA is particularly interested in receiving comments on whether a single design factor for pipelines should be used if class locations are eliminated and IM requirements are expanded beyond HCAs.

PHMSA’s notice and request for comment were published in the August 1, 2013, FR.