Pressure Relief System Revalidation and Mitigation of an Oil Refinery Case Study

The Challenge

A California oil refinery capable of refining 240 thousand barrels of crude oil per day needed to evaluate a vapor break-through scenario from a high-pressure vessel to a low-pressure vessel using dynamics. In their desire to ensure compliance with OSHA PSM regulations, the client retained ioMosaic Corporation to complete an evaluation. According to the OSHA Petroleum Refinery PSM National Emphasis Program (NEP), failure to document relief system design and design basis is one of the most common types of PSM non-compliance.

Our Approach

The project was conducted using SuperChems™, a component of Process Safety Office®. Modeling vapor gas blow-by scenario through the control valve was based on the following steps:

• Calculated the flow rate through the control valve using the detailed isometrics and control valve data. The flow rate is a function of the difference from the source pressure (high-pressure vessel) and the backpressure (low-pressure vessel). Thus, a backpressure curve was generated.
• Evaluated the currently installed relief device using the two-phase dynamic model and considering the gas blow-by stream connected to the protected equipment. Additionally, the ioMosaic team used the non-boiling liquid height model (DIERS technology) to conduct the dynamic analysis.

The Result

The existing relief device was found inadequate. As a result, the ioMosaic team conducted several two-phase dynamic simulations (mitigation) until the system was found to be adequate. The final results consisted of replacing the current relief device with two 6R8 PRVs, one set at the protected equipment MAWP, and the second PRV at the MAWP plus 5% allowable accumulation per code.

Learn More

Our mission is to help you protect your people, your plant, your stakeholder value and our planet. To learn more about how we can help you manage risk, call us at 1.844.ioMosaic.