Risk Informed Work Selection

Abstract

Asset integrity management is a life cycle concept typically initiated in the conceptual and detailed design phase of projects. Parallel with the development of equipment and system lists, the process of building maintenance job plans starts. Tools, such as criticality assessment, are used to identify the type of engineering deliverable from which the maintenance job plan is built. For a large majority of equipment and systems, original equipment manufacturer (OEM) recommended or fleet inspection, maintenance and testing (IMT) plans are adequate. For a smaller subset, more detailed plans leveraging risk-based inspection (RBI) and reliability-centered maintenance (RCM) concepts are developed building a regime of preventative maintenance focused on data collection in the commissioning and early operation of the facility. For an extremely limited subset of equipment, mostly machinery, but could include pipelines, electrical and product analyzers, the most detailed plans are developed which are highly specific to a particular equipment tag. Criticality assessment is commonly cited as a core process for prioritization of RBI/RCM plan development initially with spare parts inventories and work management later in the life cycle. International standards such as ISO 14224, Petroleum, petrochemical and natural gas industries — Collection and exchange of reliability and maintenance data for equipment, provide a framework for asset hierarchy and taxonomy which will prove to be important during the operating phase of the life cycle where surveillance and corrective maintenance data will be leverage to optimize maintenance job plans. ISO 14224 refers to IEC 60812, Failure modes and effects analysis (FMEA and FMECA), for treatment of Failure Mode Effects and Criticality Assessment (FMECA). To a large extent, ISO 60812 leaves determination of the variables to drive criticality assessment up to the operator saying only that two or more variables should be used. Variables used commonly include consequence of failure, but also maintainability and complexity. Benchmarks for criticality assessment suggest about 10% of equipment merits identification as critical (reference needed). Criticality is important as a foundation to integrity management as work linked to primary function carries an inherited technical characteristic of the equipment and systems. Over time, additional equipment and systems will be added (or removed) from critical equipment lists through continuous improvement processes such as root cause failure analysis (RCFA). With the prioritization of developing maintenance plans through fleet and RBI/RCM processes and their resultant deliverables defined, the detailed plans are identified through collaboration of technical, maintenance and operations staff specialists. Fundamentally, the process involves identification of hazards which can result in impaired primary and secondary functionality, estimation of unmitigated risk, identification of work to mitigate risk, estimation of mitigated risk, calculation of benefit-to-cost and documenting the analysis into the system of record. Consistency in the processes can be assured through application of procedures and references that typically reference a risk matrix. As each hazard is reviewed, there may be multiple failures modes (e.g. hole, crack, rupture) which needs to be considered independently. Consequence assessment is performed for a range of Safety Health Environmental and Security (SHES) scenarios associated with the failure mode. Probability assessment for the scenarios is performed using the available design parameters. The combined consequence and probability form the initial unmitigated risk basis for the scenario. Inspection, maintenance and testing activities are selected by the collaborating specialists with focus of input from technical on probability mitigation, maintenance on cost and operations on benefit. The scenarios is then revisited to document the mitigated risk.