Analysis of pressurization scenarios

An increase in pressure beyond the maximum permissible operating pressure of a device must be securely prevented at all times.

Even equipment not covered by the Pressure Equipment Directive (DGRL) because the permissible operating pressure is less than 0.5 bar _ü should be protected to prevent this from being exceeded and from loss of the integrity of the device.

Analysis of pressurization scenarios should ideally be performed by a team consisting of a chemist who knows the media and reactions involved, a plant employee who knows the particular plant well, and a safety expert. A process description and piping and instrumentation diagram should be used to discuss any possible deviations from normal operation and to consider their possible effect on pressure, temperature or change in reaction.

Mechanical, thermal and chemical causes of a pressure increase may be distinguished.

Mechanical causes for an impermissible pressure increase include, for example, failure of a flow regulator, an incorrectly adjusted pump or a final surge problem. Design cases such as gas entry or liquid entry from a higher pressure level are derived from these mechanical causes.

Thermal causes include, for example, failure of the heating steam control system, which leads to maximum heating via the shell of the vessel, or solar radiation, which leads to heating of the contents of the vessel, particularly in the case of storage tanks installed outdoors. Fire (including fire as defined in ISO 23251 or API 520/ 521) is also a thermal cause of an impermissible pressure increase. The increase in pressure in the equipment is caused either by an increase in vapor pressure or by thermal expansion of the confined medium.

Chemical causes for a pressure increase in the vessel are usually deviations from normal operation during a reaction such as incorrect dosing, blocked exhaust paths, or failure of the cooling system, which can lead to a runaway reaction. Gas-producing reactions are distinguished here from exothermic reactions. In gas-producing systems, the pressure is primarily generated by gas evolution and is largely independent of temperature. In exothermic reactions, the pressure is usually caused by an increase in vapor pressure resulting from the rapid rise temperature within the reaction system. In the case of hybrid systems, the pressure increase results from both the gas production and the increase in vapor pressure due to the exothermic reaction.

We can help you find all possible design scenarios and identify the critical cases.