overpressure protection

RKR provides world-class expertise in all areas of pressure relief analysis from well pads to petrochemicals and everything in between. This service if often referred to as a PSV or Flare Study which is a misnomer as the vast majority of the effort has little to do with the actual relief device or flare system and more to do with data collection/verification, overpressure scenario evaluation and required relief rate quantification. RKR has developed PRESSIO 2024 to integrate these basic steps performed in a typical evaluation and produce optimal, user-friendly documentation (See Sample):

Data Collection
Facility Drawings – PFD’s, P&IDs, Cause and Effect, One-Lines
Heat and Material Balance – Process Simulation or Stream Tables
Equipment – U1-A’s, Drawings, Nameplates
Rotating Equipment – Performance Curves, Mechanical Design Details
Instrumentation – Control Valve, Restriction Orifice Specifications
Relief valves – Test reports, Manufacturer’s Sizing, Inlet and Outlet Piping

RKR Tip – The data collection effort is where a great PSM and/or overall documentation management program can pay off as having this information organized and readily available greatly reduces the time and effort required to complete the rest of the steps.

Overpressure Scenario Evaluation
The analysis of potential overpressure scenarios, which are generally considered to be a single failure that could potentially result in overpressure, requires detailed knowledge of the process as well as applicable standards from various groups such as API, NFPA, ASME, DOT and ASHRAE.  Most oil and gas facilities follow API standards including API STD 520, API STD 521 and API STD 2000 with STD 521 providing detailed guidelines on typical overpressure scenarios for consideration.  RKR provides comments for each scenario considered (credible or not) that detail the key parameters considered and logic used to assess the credibility of each scenario. 

RKR Tip – The identification of overpressure scenarios is the foundation of the overall analysis.  Detailed documentation of the decision-making rationale is essential and often overlooked with a “yes or no” approach using the list of scenarios from API STD 521.  A credible scenario missed goes completely unevaluated which is vastly more important than arguing about the best pressure drop routine or a 5% difference in calculated latent heats for the fire case.

Required Relief Rate Quantification
For each credible overpressure scenario, the required relief rate to prevent overpressure is quantified using methods from industry standards, corporate standards and Recognized and Generally Accepted Good Engineering Practices (RAGAGEP).  PRESSIO 2024 brings all of these methods together in an integrated manner to deliver consistency and efficiency.

RKR Tip – The relevant industry standards are not always prescriptive and require interpretation.  If detailed corporate standards/clarifications are not available it is advisable to develop an methods and assumptions document prior to diving into the calculations.  For example, what level should be used in a vessel for determination of the wetted surface area.

Relief Device Capacity Evaluation
All of the parameters to evaluate the relief device capacity have already been set during the required relief rate calculation, therefore determining the device capacity compared to the required relief rate is relatively straightforward and completely integrated in PRESSIO 2024.  Based on the actual capacity, the inlet and outlet pressure drops for relief valves are determined to ensure stable operation, reaction forces are quantified and any potential low temperature concerns are identified.

RKR Tip – For new designs where the manufacturer is not yet known, API default areas and Kd’s are used for quoting relief devices while the most recent test records are generally the best source of information for existing installations.