Protecting Pipelines At Crossings: Are Casings Obsolete?

Tony Keane, executive director of NACE International, recently assembled a panel of NACE member pipeline corrosion control experts to answer a series of questions on the challenges involved with assessing and protecting pipelines at cased road and railway crossings.

“Corrosion professionals are charged with protecting pipelines and other structures in all types of environments and conditions, and under strict regulatory requirements,” Keane explained. “Cased pipeline crossings pose particular challenges, not only because the carrier pipes within the casings are vulnerable to corrosion, but because assessments are hampered by the difficulty and high cost of accessing these pipelines compared to those that are not cased.”

The five panelists have extensive experience with the regulations, standards, and procedures involved in assessing and monitoring cased crossings. They are Jeff Didas, corrosion project manager at Colonial Pipeline Company; Drew Hevle, principal corrosion engineer for El Paso Pipeline Group; David H. Kroon, executive vice president and chief engineer of Corrpro Companies, Inc.; Norman J. Moriber, chief corrosion engineer for MearsGroup, Inc.; and Jerry Rau, director of pipeline integrity at Panhandle Energy.

Keane: What are the benefits and drawbacks to using cased hazardous liquid and gas pipelines at roadway and railroad crossings when considering corrosion and other types of damage?

Rau: I believe that there are no benefits to cased crossings. The legacy reasoning was to provide the capability to remove or replace the carrier pipe without disturbing the roadway. In actual practice, this is not widely attempted. Greater strength or wall thickness, concrete coatings, and other methods provide protection to the pipe from mechanical damage and external loads. The downsides to these installations far outweigh any benefit.

However, having said this, there are no additional or unknown hazards to pipeline integrity because a casing exists. Like any pipeline installation or facility threats, their integrity can be managed.

Kroon: Casings have historically been used at road and railroad crossings to accommodate higher dead loads (overburden for deep pipe) and live loads (traffic). They also help prevent third-party damage, although at the greater depths of the crossings, this may have minimal benefit. From a corrosion point of view, casings should simply be avoided.

Hevle: The benefits to cased pipelines for third-party damage and overburden stresses are almost completely obviated by modern horizontal directional drilling construction techniques, and yet many agencies require casings nonetheless. The disadvantages from a pipeline corrosion point of view are many: additional design and construction costs, additional maintenance and monitoring of electrical isolation, and the problems associated with electrical shorts, including remediation, additional monitoring, and increased loads on the cathodic protection (CP) systems. Cased pipelines that require direct assessment (DA) incur much higher integrity assessment costs.