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Accurate estimates of fluid flow reaction forces are especially necessary for pressure relief systems. Substantial fluid flow reaction forces can be developed when relief systems actuate for both reactive and non-reactive systems. Specific relief systems scenarios where dynamic loads may be important include but are not limited to pressure relief caused by runaway reactions, loss of high-pressure/low-pressure interface, control valve failure, heat exchanger tube failure, etc.

Determining if and when a vessel and/or piping component is going to fail under fire exposure and/or from cold temperature embrittlement is an important factor in consequence analysis and risk assessment. This paper describes detailed methods for establishing the conditions for vessel/piping failure and whether the material of construction for vessels and piping is properly selected for fire exposure and/or cold depressuring/relief.

Research by Chiyoda, Pentair and ioMosaic showed that pressure relief valve (PRV) instability leading to flutter and/or chatter is due to the coupling of the PRV disk motion with the quarter wave pipe/fluid mode frequency without resonance. Izuchi simplified his detailed modeling analysis to restrict the inlet line length for stable PRV operation and derived an analytical expression for simple inlet line geometries.

QRA and ERS Analysis are both components of a successful Process Safety Management Program. While both studies often share the same information, they tend to remain separate, independent, studies. However, at facilities where relief valves can vent toxic and flammable materials directly to the atmosphere, these discharges can be a significant contributor to overall risk.

A properly sized reclosing pressure relief valve (PRV) can protect process equipment against a variety of overpressure scenarios. Fire exposure scenarios leading to overpressure are particularly challenging, especially where a reclosing pressure relief device provides the only means of pressure relief.

This paper discusses how RAGAGEP considerations now require evaluation and proper documentation of risk factors that are often overlooked including but not limited to: dispersion analysis, thermal radiation, noise, vibration risk, reaction forces and structural supports, metal cold temperatures due to expansion cooling and two phase flow, hot temperatures due to fire exposure and/or runaway reactions, PRV stability, chemical reaction systems, and loss of high pressure/low pressure interface.

It is a common practice to insulate storage tanks containing reactive chemicals to protect against fire exposure. While this mitigation technique is appropriate for vessels handling non-reactive chemicals, reactive chemicals storage represents a special challenge and must be examined on a case-by-case basis.

The risks of shell and tube heat exchanger (STHE) sudden tube failure scenarios are often considered in relief and flare systems design and evaluation. Scenarios involving the release of high pressure gas following a sudden tube failure, especially where the shell is filled with liquids, require the use of relief and flow dynamics for better understanding of and assessment of risks, risk reduction, and relief requirements.

The landscape of relief systems and general process safety management compliance is evolving. This evolution is due in part to enforcement or potential enforcement of RAGAGEP. Because of RAGAGEP [1, 2] considerations, oversizing a relief device is no longer acceptable or desirable from an engineering perspective and from a legal liability perspective.

Numerous scenarios can lead to retrograde and phase change (RPC) flow in relief and depressuring systems. Potential hazard scenarios considered often include, but are not limited to, depressuring during process upsets (cold depressuring), relief or depressuring under fire exposure, and relief or depressuring under runaway reactions.

Retrograde and phase change (RPC) flow considerations are important for relief and flare systems design and evaluations. RPC flow can occur in high pressure systems, including subcooled and/or supercritical flow, or at lower pressures where the starting relief conditions are close to a phase boundary.

This paper outlines the basic understanding of the operability of rupture disks, the concept of Manufacturing Design Range, ASME-dictated tolerance, and how the owner of rupture disks may inadvertently and surreptitiously slip into code violation due to misinterpretation of technicalities and testing lot-creeps.

Proper characterization of reactive systems is required to ensure the mechanical integrity of processing equipment and to avoid potential hazards such as fires, explosions, and toxic cloud dispersions. As the temperature of the vessel contents deviates from safe operating limits and becomes too high, the rate of heat production by the chemical reaction (i.e., exponential function of temperature) can exceed the processing equipment rate of heat loss and/or cooling capacity (i.e., linear function of temperature) leading to a runaway reaction.

The loss of High Pressure (HP) / Low Pressure (LP) interface has to be evaluated in order to (a) ensure that the downstream equipment can handle the energy and/or mass accumulation and (b) to also ensure that the upstream equipment can handle the rapid depressurization.

With the increased regulatory focus on pressure relief and flare systems (PRFS) design basis, many companies are in the process of updating their existing relief systems design documentation.