United States Department of Transportation
i
Natural Gas Encasement for Highway Crossings
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2015-03-01
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[PDF-2.31 MB]
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Abstract:The University Transportation Center for Alabama researchers examined the Alabama Department of Transportation’s current policy regarding the encasement of natural gas and hazardous liquid pipelines at roadway crossings. The group collected information from a variety of sources regarding the benefits and drawbacks of encasement, including current standards, state policies, interviews with utility company personnel and utility contractor personnel, academic and non-academic publications, and gas pipeline incident reports. Though PHMSA incident reports indicate that encasement reduces excavation damages, the group recommended that the encasement of natural gas and hazardous liquid pipelines should not be mandatory at highway crossings except for special situations already cited in the ALDOT Utilities Manual. Instead, natural gas and hazardous material pipeline designers should follow the Code of Federal Regulations (CFR) Title 49 Volume 3 -- Parts 192 and 195, respectively -- which by reference includes all the necessary standards for pipeline design. The following findings support the conclusions: • PHMSA recommends uncased crossings where practicable, • ASME 31.4 specifies that uncased crossings are “preferred” for hazardous liquid pipelines, • NACE International (formerly the National Association of Corrosion Engineers) considers casings a corrosion hazard and recommends against them, • Though costs vary by installation, a cased crossing may typically cost twice as much as an equivalent uncased crossing • Several hypothesized benefits of casing (such as usefulness for replacing damaged pipes at road crossings) have not been proven in service, • The risk associated with uncased crossings appears to be orders of magnitude below acceptable limits, and • The majority of city and local road crossings in Alabama are uncased to no apparent detriment.
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