The American Petroleum Institute has formed a methodology for tank overfill protection with the publishing of its newest edition to API 2350. Taking a few pages from this standard can help in implementing an effective tank overfill prevention program.
API 2350 Edition 4 outlines the minimum requirements needed to comply with the latest best practices to prevent tank overfills in petroleum facilities. Some might ask, “Why should I care if I don’t have a large oil tank?” It is the approach that API 2350 Edition 4 takes that makes it relevant to any operator of tanks that are at risk of an overfill.
To be compliant with the API 2350 standard, certain criteria must be satisfied in order to prove that the risk of overfill has been reduced to an acceptable level. API 2350 now requires the performance of a risk assessment for each tank by evaluating the likelihood and consequences of an overflow. This enables an organization to prioritize and allocate resources appropriately.
To aid in this effort, the standard requires that each tank be categorized into three groups. This classification process makes it easier to evaluate the existing tank gauging configuration on each tank.
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The following is a general overview for each of the categories. While the standard does not state which category is best, it can be presumed that the higher the category, the more reliable the tank gauging system is.
Category 1: In this configuration, all operations are performed manually by a local operator. Basically, this means that an actual person has to be right there by the tank to shut the valve during a receipt in order to prevent an overflow. Also, there are no transmittable alarms or equipment to annunciate alarms. So, while there may be tank level gauging equipment installed, it is entirely up to the operator to know when a high level has been reached.
Category 2: In the second category, the tank is equipped with sensors and alarms to notify personnel of a high level. This way operators don’t have to be right by the tank to know if there is a risk of overfill. Furthermore, shutting off the valve no longer requires an operator to be there next to the tank. Since the sensors and alarms can transmit level information, an operator may be able to cancel a receipt by closing the valve remotely from a control room.
Category 3: The only difference between the second and third categories is that a Category 3 tank is equipped with an independent high-level alarm. This category is theoretically more reliable since it has a backup sensor in case the primary one fails. Just like Category 2, the operator may cancel a receipt from a remote location or locally.
Automatic Overfill Prevention System (AOPS): This final category is separate from the first three categories. The AOPS is never intended to be used on its own, but in addition to one of the other configurations (usually Category 2 or 3). Sometimes AOPS is referred to as Category 4. The advantage to AOPS is that it is capable of executing a shut off without human intervention.
Implementing a tank overfill prevention standard like suggested in API 2350 is well worth the investment. Nobody wants to be responsible for a disastrous spill—but there is more to it than prevention. Companies that execute a management system to prevent overfills may also realize optimization in their normal day-to-day operations.
By dutifully following a well-developed and structured system, tank owner/operators can be more efficient in the way they manage their resources. The question should not be whether to implement an OPP like API 2350, but when.
To download the API 2350 standard, visit www.api.org.
Caleb Hanson is a graduate of Utah State University and is currently working for Automation Products Group as a technical support specialist. He enjoys assisting professionals to overcome their tank level control challenges and has built a reputation as the “go to guy” for such applications.
This post is based on a more detailed feature article that will appear in the March 2013 issue of Flow Control magazine. If you are not yet a subscriber to Flow Control magazine, you can register for a free subscription here.
