Low Pressure Does Not Equal Low Risk: Strategies to Protect Tanks Against Overpressure and Undervacuum

Industry personnel often perceive low pressure tanks as being less dangerous than pressure vessels, particularly due to their less stringent standards for design and construction. However, this approach is mistaken as it overlooks the fact that a typical low pressure tank can often contain more material and be more easily be opened to the atmosphere in response to a process upset when compared with a typical pressure vessel. This paper will discuss types of safeguards to prevent overpressure and undervacuum of low pressure tanks, will identify the strengths and weaknesses of these safeguards using consequence modeling techniques where applicable, and will recommend overall safeguarding strategies in order to best utilize the strengths and mitigate the weaknesses of the available safeguards.

Consequence Modeling Examples:

• Forming flammable atmospheres when venting pressure to atmosphere via conservation vents and/or emergency vents
• Forming flammable internal atmospheres when pulling in air to break vacuum via vacuum vents and/or conservation vents
• Asphyxiation hazards due to venting inert internal atmosphere indoors or in a congested area
• Atmospheric venting via poorly maintained flame/detonation arrestors
• Hazardous liquid relief to secondary containment via overflow line