In the event of an imbalance in the volumetric flows in and out of a container, a change of pressure can result within the container. The flow rate entering and exiting the container can be determined using common engineering calculation techniques, either by evaluating the capacity of a single limiting source term or single piping component, multiple piping components in series, the limitations of a fluid driver, or the combined effect of the fluid driver and the intervening piping system. Several cases of overpressure scenarios are evaluated in this manner, including heat exchanger tube failure, inlet control valve failure, and inadvertent valve opening.

The transfer of heat into or out of a constant volume container results in an attempt of the entrapped fluid to change in overall density, leading to pressure increases or decreases. The change in fluid…

When performing pressure relief analysis, the blocked system outlet is one of the most common overpressure scenarios requiring consideration.  A blocked system outlet can occur on almost any piece of equipment.  A blocked outlet may…

All control valves, regardless of their fail-safe position, have the potential to go wide open.  Failure open of an inlet control valve is typically considered an applicable overpressure scenario for a pressure vessel when the…

Many of the relieving requirements for credible overpressure scenarios we calculate implicitly assume that the only mass/energy allowed to leave the system is through the relief device; however, there are some instances of reasonable attempts…

API Standard 521, 6th Edition, §4.4.12.4.1 provides an equation (shown below) for the calculation of the pressure rise due to hydraulic expansion of a non-boiling liquid1.  The calculation is comprised of four basic components: the…

We recently encountered cases where the corrected hydrotest pressure needed to be determined, and thought it would be useful to share the calculation process.  The cases in question were various tube ruptures potentially affecting a…

Following the release of the most recent Fireside Chat on pressure relief critical controls, we received a question specific to critical check valves, or non-return valves (NRVs), and our thoughts on taking credit for them…

There are several controls used in a facility in various ways that directly affect the relief system design or design basis, and are critical to the design of a pressure relief system.  While there are…

An inadvertent mixing of hot and volatile fluids can result in overpressure if the volatile fluid is vaporized and sufficient volumetric accumulation occurs.  Hot fluid temperatures exceeding the bubblepoint temperature of the volatile fluid is…