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What Is API 2000? | Process Engineering Glossary
What Is API 2000?
API 2000, formally titled Venting Atmospheric and Low-Pressure Storage Tanks, is a standard published by the American Petroleum Institute that establishes requirements for both normal and emergency venting of atmospheric and low-pressure storage tanks. It covers the vent capacity needed to prevent a tank from developing excessive internal pressure or vacuum during routine operations like filling and emptying, as well as under emergency conditions such as external fire exposure.
The standard provides calculation methods and reference tables for determining required venting capacity based on tank size, operating conditions, and the specific normal or emergency scenario being evaluated, giving engineers a recognized basis for both pressure and vacuum relief device sizing on this class of vessel.
Applications of API 2000
Normal Venting Requirements
Routine tank filling and emptying displaces vapor or draws in air at rates that have to be accommodated by properly sized vents; API 2000 provides the basis for calculating this normal venting requirement so a tank isn’t over- or under-pressured during everyday operation.
Emergency Venting for Fire Exposure
When a tank is exposed to an external fire, the contained liquid can generate vapor far faster than normal operating conditions require venting for. API 2000 includes specific methods for calculating this emergency venting capacity, which is typically the larger and governing requirement compared to normal operating vents.
Tank Design Coordination
Venting requirements determined under API 2000 directly inform the selection and sizing of both pressure and vacuum relief devices on the tank, tying the standard closely to the tank’s overall mechanical design and the specific relief hardware ultimately installed.
Benefits of Knowing API 2000
Provides a recognized calculation basis. Using API 2000’s methods gives a documented, industry-recognized basis for venting capacity that stands up to regulatory and insurance review.
Separates normal and emergency requirements. Explicitly distinguishing routine operating venting from fire emergency venting ensures neither scenario is under-addressed by a single generic calculation.
Coordinates tank and device design. Following API 2000 keeps the tank’s mechanical design and its installed relief devices aligned against the same governing venting requirement.
Limitations to Consider
Scope is limited to atmospheric and low-pressure tanks. API 2000 applies specifically to atmospheric and low-pressure storage tanks; higher-pressure vessels fall under different codes such as ASME Section VIII, and applying API 2000 methods outside its intended scope isn’t appropriate.
Requires accurate input data. Calculated venting requirements are only as reliable as the tank dimensions, fluid properties, and operating rates used as inputs, and generic or outdated data can understate the actual requirement.
Doesn’t replace a full relief system evaluation. API 2000 addresses tank venting specifically; a complete relief system design may still need to account for other scenarios and equipment beyond what the standard directly covers.
API 2000 FAQ
How does API 2000 relate to vacuum relief valve selection?
API 2000’s normal and emergency venting calculations, published by the American Petroleum Institute, directly determine the required capacity for both pressure and vacuum relief valve devices installed on a storage tank, making it the standard reference point for sizing both sides of a tank’s set pressure and venting protection.
Why does API 2000 apply to atmospheric vessels specifically rather than all pressure vessels?
Atmospheric vessels and low-pressure tanks have thin-walled construction that behaves very differently under overpressure and vacuum than a thick-walled pressure vessel, which is why they’re governed by a dedicated venting standard rather than the same code used for higher-pressure pressure vessel design.
How does API 2000 interact with relief device selection like pilot-operated valves?
Once API 2000 establishes the required venting capacity, that number becomes the target the selected device, whether a simple weight-loaded vent, a pilot-operated relief valve, or another design, has to meet, tying the standard’s output directly into device-level relief valve sizing.
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