Pressure Relief Sizing
Relief sizing
In order to run a safe manufacturing process, it is critical to understand the individual reactions within the process. These reactions can be exothermic or endothermic, each of which can be hazardous. These reactions could be a part of the desired chemistry of the process. However, these reactions could also be caused by undesired chemistry such as side reactions. Environmental changes can also result in undesired chemistry. Therefore, identification and assessment of these reactions is important especially during the scaleup of an operation. Belmont Scientific provides cost effective testing which is listed in the table below.
| Properties Measured/Estimated | Standard or Test Technique | Key Test/Instrument |
|---|---|---|
| Onset temperature Heat flow rate Heat of melt Latent heat of evaporation Melting/boiling temperature Enthalpy of endotherm Enthalpy of exotherm | ASTM E537 Standard Test Method for the Thermal Stability of Chemicals by Differential Scanning Calorimetry (DSC) | Differential Scanning Calorimeter (DSC) by TA Instrument |
| Heat capacity | ASTM E1269 Standard Test Method for Determining Specific Heat Capacity by Differential Scanning Calorimeter (DSC) | Differential Scanning Calorimeter (DSC) by TA Instrument |
| Onset temperature Temperature rise rate Pressure rise rate Heat of reaction Amount of gas generated | ASTM E1981-98 (2012)e1 Standard Guide for Assessing Thermal Stability of Materials by Method of Accelerating Rate Calorimetry (ARC) | ARC from CSI and ARC 254 from Netzsch Group of Selb, Germany (High Thermal Inertia) |
| Onset temperature Temperature rise rate Pressure rise rate Heat of reaction Amount of gas generated Vent flow regime | ASTM E1981-98 (2012)e1 Standard Guide for Assessing Thermal Stability of Materials by Method of Accelerating Rate Calorimetry (ARC) | Vent Size Package 2 (VSP2) from Fauske & Associate, LLC, Burr Ridge, IL USA (Low Thermal Inertia) |
On-site Calorimetry Testing: BSI provides on-site thermal hazard testing services using DSC, ARC®, and VSP2.
Shock Sensitivity Testing: BSI uses a blasting cap test method to characterize materials for shock sensitivity. Test uses about a 15ml sample size and is a Go/No-Go test. This test can also be performed on-site.
We design and validate pressure relief systems (PSVs/PRVs) for chemical, petrochemical, battery, and specialty process industries. Our relief sizing service covers non-reactive and reactive PSV scenarios, two-phase relief, and advanced kinetic modeling for reactive systems — backed by lab calorimetry and best-practice engineering.
Our testing programs are tailored for:
Process safety evaluations and hazard assessments
Emergency relief system design and DIERS vent sizing
Reactive chemical screening and compatibility assessments
Our Core Services
1. PSV Relief Sizing — Non-Reactive Systems
Full relief sizing for hydrocarbon, inert, and other non-reactive process streams:
Identification of credible overpressure scenarios (blocked discharge, thermal expansion, fire, relief from compressor or pump failure)
API 521 / API 520-compliant sizing calculations (liquid, gas, vapor) and PSV selection support
Liquid flashing analysis and two-phase decision logic when applicable
Valve metering and inlet piping recommendations to avoid chatter or blowdown issues
2. PSV Relief Sizing — Reactive Systems
Specialized relief sizing where the source term can grow due to chemical reaction:
Reaction-driven scenario development (e.g., runaway, self-accelerating decomposition)
Lab-supported heat and gas generation rates
Determination of required relief area and set points based on worst-case adiabatic/dynamic scenarios
Integration of kinetic modeling outputs to capture realistic heat/gas evolution
3. Two-Phase Relief & Multiphase Flow Design
Design and modeling for relief of mixed liquid/vapor streams:
Flashing analysis (isenthalpic, equilibrium estimates) and two-phase mass flow calculations
Evaluation of inlet piping and downstream backpressure effects on capacity
Liquid-droplet carryover, slugging and piping stress considerations
Recommendations for knock-out drums, two-phase separators, or pilot relief systems if required
4. Kinetic Modeling for Reactive PSVs
We translate lab data into robust kinetic models used for safe relief sizing:
- Fit kinetic parameters (Arrhenius, nth-order, autocatalytic, etc.) to calorimetry data
- Predict heat release rates (HRR), gas generation, and time-to-maximum rate for scenario bounding
- Couple kinetics to thermal/pressure network models to compute required relief capacity under realistic kinetics
- Provide sensitivity studies (uncertainty, scaling from lab to plant) and conservative bounding approaches
Our Methodology :
Why Choose Belmont Scientific?
FAQ:
1. Which standards do you follow for non-reactive relief sizing?
We follow industry practice and codes (example: API 520/521, ASME recommendations) for scenario identification and sizing methodology
2. What are the industry standards or guidelines for reactive relief system design?
- DIERS Guidelines (AIChE) – foundational framework for reactive vent sizing
- API 520 / 521 – Relief system design and venting of reactive systems
- CCPS Guidelines for Safe Handling of Reactive Chemicals – kinetic data and modeling practices
3. Why are reactive PSVs more complex to size than non-reactive ones?
Reactive systems can generate heat and gaseous products that accelerate over time (runaway reactions). Sizing must account for the worst credible rate of gas production and heat release — often requiring laboratory calorimetry and kinetic modeling to quantify the source term.
4. What exactly is two-phase relief and when is it needed?
Two-phase relief occurs when the fluid discharging through the PSV contains both liquid and vapor (e.g., flashing during depressurization or entrained vapor). It’s needed whenever flashing, entrainment, or liquid carryover into relief piping is credible and affects flow capacity or downstream handling. Two-phase flow behavior is more complex: flow efficiency can drop, choking behavior differs, and mass flux depends on quality (liquid fraction). In many cases, two-phase discharge requires a larger relief area or additional separation equipment downstream.
5. What lab data do you need for kinetic modeling?
Typical inputs are heat flows, onset temperature of self-heating, self-heating and pressure rise rates, heat of reaction, pressure/temperature traces, and venting behavior. These allow determination of activation energy, frequency factor, reaction order, and gas yield.