3.2 Pipeline Incidents
In the US, the Department of Transportation (DOT) regulates the design, construction, operation and maintenance, and spill response planning for CO2 pipelines. The DOT administers pipeline regulations through the Office of Pipeline Safety (OPS) within the Pipelines and Hazardous Materials Safety Administration (PHMSA). Although CO2 is listed as a Class 2.2 (non-flammable gas) hazardous material under DOT regulations the agency applies nearly the same safety requirements to CO2 pipelines as it does to pipelines carrying hazardous liquids such as crude oil, gasoline, and anhydrous ammonia [Ref 12].
Statistics on pipeline incidents can be found at OPS within the U.S. Department of Transportation, Pipeline and Hazardous Materials Safety Administration [Ref 13], and is summarized below:
- In the period 1986–2001: 11 incidents related to pipeline transport of CO2 are reported with a total of one fatality and two injuries. According to the incident log, the fatality was related to welding work and not as a direct consequence of pipeline operation. 9 of the incidents were related to the pipeline (all onshore), whereas the remaining two occurred at the pumping station.
- In the period 2002– 2008: 18 incidents related to pipeline transport of CO2 are reported with no fatalities and injuries. 9 of these incidents were solely related to the onshore pipeline itself, whereas the remaining were related to incidents at pump/metering stations or terminal/tank farm piping and equipment, including sumps.
The failure modes of all the 29 reported incidents from 1986–2008 are grouped and presented in Figure 3-1.
Figure 3-1: Grouping of reported failure modes for CO2 pipeline systems
In comparison to the above statistics, there were 5,610 accidents causing 107 fatalities and 520 injuries related to natural gas and hazardous liquids (excluding CO2) pipelines during the period 1986–2006. Reported data for natural gas pipelines in the US showed the principal causes of pipeline accidents were outside force (35%), corrosion (32%), other (17%), weld and pipe failures (13%) and operator error (3%). The category “outside force” includes “human error” accidents principally as a result of third party damage by contractors, farmers and utility workers. The “other” category includes incidents such as vandalism, train derailment and improper operation of manual valves [Ref 14].
A mile-by-mile comparison is made by Gale and Davidson [Ref 14], and according to their study CO2 pipelines have a frequency of incident of 0.33 per 1000 km per year, whereas natural gas and hazardous liquids pipelines have a frequency of 0.17 and 0.82, respectively.
Table 3-1: Statistics of pipeline incident in the USA [Ref 14]
|Natural gas transmission (1986–2001)||Hazardous liquids (1986–2001)||CO2 (1990–2001)|
|No. of incidents||1287||3035||10|
|No. of injuries||217||249||0|
|No. of fatalities||58||36||0|
|No. incidents (per 1000 km pipeline per year)||0.17||0.82||0.33|
As seen from the numbers in Table 3-1, the frequency of incidents of CO2 pipelines between 1990 and 2001 was higher than that of natural gas pipelines. It is not clear why the frequency of incidents of CO2 pipelines is higher. A possible explanation could be that the confidence interval is larger due to the low sample number. Analysts suggest that, as the number of CO2 pipelines expands to support CCS, statistically the number of incidents involving CO2 should be similar to those for natural gas transmission [Ref 15].