This recommended pipeline risk assessment methodology is similar to SRA (Structural Reliability Analyses) and LSD (Limit State Design) or LRFD (Load and Resistance Factor Design). This is coincidental, since the methodology was developed independently from these techniques. However, despite the similarities, there are key differences.
- Focus on engineering principles rather than incident history
- Accommodates either point estimates or probability distributions as inputs (Level 1 vs Level 2,3,4 methods)
- Accommodates various definitions of ‘failure’ (choice of limit state)
- Provides platform for various levels of rigor in evaluation (e.g., remaining strength calculations)
- Offers more efficient solutions compared to previous, more-prescriptive methods (e.g., use of fixed safety factors)
- This recommended risk assessment approach insists on independent evaluations of exposure, mitigation, resistance, and consequence. SRA and LSD methodologies will often use the equivalent of ‘mitigated exposures’ in their analyses. For instance, the frequency of excavator impact frequently includes associated mitigation measures such as depth of cover, signs/markers, public education, one-call systems, etc. regardless of how variable those measures might be along a pipeline’s length. While not necessarily limiting the utility of SRA or LSD, the confounding of these ingredients can result in serious limitations in a risk assessment.
- This recommended risk assessment approach deemphasizes the underlying probability theory (which is common to both this and the SRA/LSD approaches) and focuses on making the methodology more transparent and approachable to a non-technical audience.
- We can take some comfort in the fact that this newer risk assessment methodology shares key aspects of the older and well-tested SRA and LSD methods.
- We should also recognize that in at least one key aspect, this methodology avoids a limitation in the older approaches. That is the separation of confounding factors that usually occurs in SRA, LSD. By insisting that exposure, mitigation, and resistance be independently measured, the confounding is avoided.