Finding the optimal balance between risk and inspection-activity costs can sometimes be tricky. Risk-based inspection (RBI) is a technique aimed at assessing the possible loss of containment due to material deterioration in pressurized equipment. It is a fundamental tool for the integrity management process focused on assets in facilities, as it makes it possible to manage threats through the inspection of installations. In this article, our experts Nadia Jerez, Senior Engineer, and Oscar Gómez, Engineer MSc, explain how their team developed an algorithm that performs quantitative risk calculations and recommends inspection frequency for a client in our South America region.
RELEVANCE OF RBI FOR THE INDUSTRY
Several codes (e.g. API 510, API 570 and API 653) suggest inspection frequencies and activities based on the type of installation and an asset’s operational conditions. However, such recommendations are fixed and may not reflect the actual condition of the asset. The RBI framework described in the API RP 581 standard allows performing quantitative assessments to fine-tune inspection frequencies and define a specific inspection plan for each asset.
The RBI inspection plan produced according to this methodology should be complemented with an additional comprehensive set of integrity operating windows (IOWs, in accordance with API RP 584) for each process unit and a rigorous management of change (MOC) program. The combination of these efforts will provide the basis for the complete integrity management of pressure vessels and piping in the refining and petrochemical process industry.
RELEVANCE OF RBI FOR THE OPERATORS
The main output from an RBI assessment is the inspection plan that addresses different ways to manage risks on an individual installation level. This approach highlights risk from a safety/health/environmental perspective and/or from an economic standpoint. Then, the implementation of this plan provides either an overall reduction in risk for the assessed facilities and installations or an acceptance/understanding of the current risk.
Figure 1 - Pareto rule; much of the total risk is concentrated in a small percentage of the installation, 80 to 20%
The RBI inspection plans also identify equipment that does not require inspection activities or some other form of mitigation because the risk is not high enough to exceed acceptable levels. This way, inspection and maintenance activities can be prioritized based on a cost-effective approach (see Figure 2 below).
Figure 2 - Examples of the RBI investment compared to inspection and maintenance savings and production-cost savings 
RBI FOR GASMAR
ROSEN completed a comprehensive risk-based inspection study for a GASMAR facility at the Chilean Pacific coast. The client required assistance in the optimization of inspection activities for all pressure vessels and piping in a liquefied petroleum gas (LPG) terminal using the API RP 581 methodology.
WHAT WAS THE CHALLENGE?
The ROSEN project team started by executing a high-level qualitative assessment that provided the client with an overview of the risk levels in different sections of the terminal and helped to prioritize the assets. Then, the installations were assessed using quantitative methods based on the API RP 581 methodology. As a result, the client was able to understand the current risk level (as per probability and consequence of failure) of the process and utility installation and could then define inspection plans for each of them.
WHAT WAS THE OUTCOME?
The team developed an algorithm that performs quantitative risk calculations and recommends inspection frequency. Based on the final risk matrix results for both the pressure vessels and the piping, our experts detected no high-risk features in any of the analyzed assets.
Figure 3 - Final risk matrix result for pressure vessels (left) and piping (right) in GASMAR facility. In all the analyzed assets, there are no high-risk results
As a result, an optimal balance between risk and inspection-activity costs was recommended.
Figure 4 - Summary of the inspection activities for pressure vessels (PV) and piping for the next ten years
Ultimately, the quality of ROSEN’s report surpassed the client’s expectations. This project adds to the list of RBI assessments ROSEN has executed worldwide in the past ten years, for onshore and offshore facilities alike. Soon, RBI functionality will also be available in ROSEN’s integrity management platform NIMA.
 DNV presentation at IAPG Congress, November 2006, Bs. As., Arg.