BG&E’s Experience With Cased Carriers On Transmission Lines

The Pipeline Safety Improvement Act of 2002 is federally mandated legislation that addresses risk analysis and integrity management programs for pipeline operators. It also directs the U.S. Department of Transportation (DOT) to adopt regulations relating to integrity management. DOT finalized these regulations on Dec. 17, 2004.

Natural gas transmission pipeline operators were required to begin conducting assessment by June 17, 2004, have a management program in place by Dec. 17, 2004, and to complete baseline assessments of pipe in high consequence areas (HCAs) by 2012.

This included challenging External Corrosion Direct Assessment (ECDA) situations, such as: river, road, and expressway crossings; casings; bare pipe; and AC interference. These ECDA areas are difficult to assess for most LDCs with transmission lines.

As a result, “What are we going to do about casings?” became an oft-repeated phase for Baltimore Gas & Electric’s (BG&E’s) pipeline integrity team back in 2007. There were approximately 70 cased crossings identified on the company’s transmission pipe in HCAs regulated by the transmission integrity rule.

BG&E’s assessment method for transmission lines is ECDA. Pipe inside of casing is covered by the rule, but cannot be indirectly inspected or directly examined.

In 2007, the 2012 deadline for finishing the baseline assessment seemed far off; however, experience suggested the deadline was right around the corner.

The Pipeline Integrity Team had four options for dealing with casings. The first option was to see whether the cased carriers really were in HCAs, by definition. When the transmission system was initially examined for delineation of HCAs, in some instance two HCAs were joined into one if the distance between them was a few hundred feet. Occasionally a cased carrier was found to be in that area. The second option was to use alternative technology to assess the condition of the carrier pipe inside the casing. Guided wave (GW) was selected as the assessment method. The third option was to remove the casing completely. It was unclear how that would be accomplished, but was worth investigating. The fourth option was to completely replace the cased carrier pipe.

The team made an initial assessment of which cased carriers in the system were not in HCAs, which would be assessed by guided-waved, which could be removed and which would probably be replaced. An initial schedule and plan for all cased carriers was developed, but first a pilot program would be developed and executed in order to determine costs and operational concerns – procedures, permitting, traffic considerations, coordination of excavation contractors and GW contractors.

Pilot Program
A pilot program was conducted in 2008. Five cased carriers were selected. All were under secondary roads. Four of the casings were between 45-50 feet long. One casing was 84 feet long. All were GW tested. Two of the casings were completely removed.
This pilot program identified several areas of concern: