Communiqués

TSB # P 09/97

(For release 17 July 1997)

(Hull, Quebec) - The Transportation Safety Board of Canada (TSB), in its final report on the rupture and fire on two natural gas pipelines near Rapid City, Manitoba, has identified deficiencies involving the emergency shut down (ESD) of these pipelines. The Board has issued two safety recommendations to address these deficiencies and has expressed concern about the horizontal spacing between adjacent pipelines. The Board also notes that significant safety action has already been taken to address other concerns arising from this occurrence.

The accident took place in the early morning of 29 July 1995, at TransCanada PipeLines Limited (TCPL) compressor Station 30, about three kilometres southeast of Rapid City. The Board concluded that the initial rupture and fire occurred on a 42-inch natural gas pipeline (100-4) as a result of a pre-existing stress corrosion crack (SCC) in a piece of pipe downstream of the compressor station. This piece of pipe had been fabricated in the field and coated with polyethylene tape.

The resulting explosion and fire destroyed much of the communications system at the compressor station and made it difficult to shut off the flow of gas in line 100-4. As a result, natural gas pipeline 100-3, a 36-inch line adjacent to line 100-4, sustained fire damage that weakened it, and it too ruptured and caught fire. A 48-inch natural gas pipeline (100-5) which passed under lines 100-3 and 100-4 sustained minor fire damage to the coating of the pipe.

The TSB investigation also discovered a problem with the supervisory control and data acquisition (SCADA) system. This fault in the SCADA system delayed the shutdown and isolation of lines 100-4 and 100-3. TCPL has advised the TSB that these faults in the ESD and isolate commands have now been corrected.

Since the rupture, TCPL has expanded its SCC management program of hydrostatic re-testing, soils modelling to assist in determining potential SCC locations, investigative digs, and pipe replacement.

Shortly following this accident, the National Energy Board (NEB), the pipeline regulator, ordered a public inquiry into SCC occurrences on Canadian oil and gas pipelines. The report, released to the public on 19 December 1996, contained 27 recommendations to promote public safety on buried oil and gas pipelines in Canada. The TSB believes that implementation of the measures recommended by the NEB will go a long way towards better managing the risks associated with SCC in pipelines.

Even though considerable action has been taken, the TSB is concerned that the regional operating controller was unable to effect a rapid shut-down of the system. This inability to shut down the system led to considerable collateral damage in and around the compressor station and to the rupture of line 100-3.

The Board believes that ESD systems should be hardened against explosive forces and fires, and should be capable of automatically isolating flow of product to an accident site, overriding other commands if necessary, until it has been verified that it is safe to reactivate normal operations. To that end, the Board has recommended that:

The National Energy Board reassess the design provisions for "emergency shut-down" anywhere in the pipeline system with a view to ensuring the rapid isolation from the flow of product in the event of a ruptured line. [P97-01]

In addition to the problem with the remote ESD, there also was a problem with the on-site ESD. The TSB understands that compressor stations are often unstaffed. Nevertheless, as a backup to the remote system defences for ESD, company employees should be capable of ensuring an ESD locally. In addition to ESD equipment and training, there should be a feedback loop, so that employees can determine if the shut-down has been initiated. The Board has therefore recommended that, as a part of the design review of Recommendation P97-01:

The National Energy Board reassess the adequacy of the emergency shut-down systems at compressor stations, with a view to ensuring that operators are aware of the operating status of the system under emergency conditions. [P97-02]

The Board also noted that there are currently Canadian Standards Association requirements for vertical spacing between pipeline systems in Canada; these requirements address the safety issues associated with pipeline systems that cross over each other. However, there are no similar requirements for the horizontal spacing of pipeline systems. The Board is concerned that current spacing standards may be inadequate in this regard, especially considering the potential consequences of a natural gas pipeline failure, particularly in highly populated areas.

The Transportation Safety Board of Canada is an independent agency operating under its own Act of Parliament. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.

-(30)-