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The following post was originally published on Magnetrol International's blog, which covers level and flow measurement solutions and application issues.

In the aftermath of several tragic tank overfill incidents in recent years, the American Petroleum Institute revised its API RP 2350 recommended practice to address malfunctioning or insufficient tank level gauging. During the past few months, we’ve received numerous questions about these new recommendations for overfill protection, and will be sharing answers to the most frequently asked questions on this blog during the next few weeks.

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Question: Is API RP 2350 required?

Answer: API RP 2350 is not a regulation or a law. It is a recommendation that API published as a self-policing tool for the industry. We do know that insurance companies are asking their clients to comply with the new API RP 2350 standards–and that your liability will be mitigated if an incident should occur and you have followed the recommendations of API RP 2350. So, while it’s not a law but, it makes good sense.

Question: How can an owner/operator determine if their proof testing of overfill prevention system (OPS) equipment is adequate?

Answer: With proof testing, you are trying to determine the status of all of the components of your OPS, and a wet test is the ultimate way to see if the entire loop is working correctly and operating as designed. When you do a proof test of a single device, you can use an electronic simulation that sends a signal back to the control room or to the operator to indicate that the device is in a functional state. Many proof tests are simply an electronic simulation, perhaps just a relay positioning change. But the ultimate proof tests are the ones that physically cause the device to move or actually simulate the fluid.

Proof testing per API RP 2350 does not require the completion of a wet test; however, performing a simulation and doing a test will show you if a device is working or not. For devices that sit idle for long periods of time before any fluid reaches them, it is especially critical to test them on a regular basis to ensure that they are working properly.

Question: Does API RP 2350 apply to upstream industries or only to refining?

Answer: It can apply across both upstream and downstream markets. The API RP 2350 recommendations define an eligible above-ground tank by the size of the tank, how the product is delivered, and which type of liquid is in the tank. These are the only stipulations, and you can apply them anywhere along the line.

Question: Are tank categories 1 (fully attended) and 2 (semi-attended) still in use as technology improvements have taken place?

Answer: The API RP 2350 4th edition update is a significant change from the 3rd edition. The 4th edition introduces many new recommendations, including the tank categories and the requirement for an independent high level alarm. Due to these new–and very specific recommendations–many operators are finding that their equipment is not suitable for a category 3 (unattended) tank.

Fortunately, the specification does give you time to update your equipment and provides options that you can use to categorize your tanks in the meantime. But, if the equipment is not automated and does not meet category 2 or 3 requirements, you must have the site attended at all times during product transfer.

Question: What’s the difference between an automated overfill protection system (AOPS) and the SIS safety instrument system (SIS)?

Answer: The AOPS is specific to the tank itself and to the filling operation or process, which is part of the procedures that you use to handle an overfill situation at your facility. The SIS also applies to the process side of the safety shutdown system, but ultimately an SIS device provides higher reliability and has a higher safety standard. Having an SIL- or SIS-rated device will increase the reliability and would be beneficial during the safety shutdown of a device.

Many systems used in automatic tanks systems are SIS- or SIL-rated, but it is up to a facility’s owner/operator to determine if they want to go with that type of process. The procedures and the testing that you use for the various levels of concern will also help determine whether you need to invest in this level of technology.

Question: Does API 2350 also apply to tank transfers in a refinery?

Answer: API 2350 does not specifically apply to tank transfers, but the specification is designed to protect any given tank against overfill. So, if a tank is filled via a pipeline or a marine vessel and fits all of the other API 2350 criteria, it should be equipped with an OPS according to the specification.

In addition, API 2350 focuses on the tank and how the tank is used, rather than one specific transfer. For example, if two tanks are in the same facility, one operator controls the flow of the product between both tanks. However, if the tanks are located at different facilities or remote locations where there is a second operator, the overfill protection would definitely be needed because two different parties are involved in the receipt.

To read Magnetrol's Part II post in this FAQ series, click here. To read Magnetrol's Part III post in this FAQ series, click here

Also, you can view Magnetrol's On-Demand Webinar on API RP 2350. Click here to register.