In Australia (and the UK), pipeline operating companies have a regulatory obligation to ensure that their assets are designed, constructed, operated and maintained so that risk to people and the environment is as low as reasonably practicable (ALARP). In many routine cases, demonstration that risk is ALARP is a matter of compliance with relevant technical standards. There are some cases, however, that are more complex.

If a pipeline has been subject to significant urban encroachment and does not conform to current design standards for this service, how does a pipeline operator decide whether risk controls are sufficient? In Australia, rather than either ‘grandfathering’ requirements or mandating retrospective compliance with new standards, operators are required to ensure pipelines are safe and that risk levels are acceptable. The answer in cases such as this is a matter of judgment and we have legal, moral and reputational responsibilities to get decisions such as this right. There is currently no formal requirement in the US for pipeline risks to be ALARP, although the concept is gradually being introduced to US industry safety law. Examples include US offshore well control rules, California refinery safety regulations and the nuclear sector concept of ‘as low as reasonably achievable’.

In this paper, we demonstrate application of the ALARP process to a case study pipeline built in the 1960s that has been heavily encroached by urban development. The Australian risk-based approach required formal ALARP assessment including consideration of options to reduce pressure, relocate or replace the pipeline, or increase the level of physical or procedural protection.

Current and predicted operating conditions on this existing pipeline allowed reduction in operating pressure in some of the encroached segments, sufficient to achieve the equivalent of current Australian requirements for ‘No Rupture’ in high consequence areas for new pipelines. In other areas this was not achievable and a lesser degree of pressure reduction was instigated, in combination with physical barrier protection. The physical barrier slabbing comprised over 7 km of 20 mm thick high-density polyethylene (HDPE) slabs, buried above the pipeline. This approach was new in Australia and required field trials to confirm effectiveness against tiger tooth excavators and rotary augers.

These upgrades to the case study pipeline have significantly decreased the risk of pipeline failure, by reducing both likelihood and consequences of accidental impact. In combination with rigorous procedural controls such as patrol surveillance and community liaison, real risk reduction has been achieved and ALARP has been demonstrated.

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