API RP 2350 Overfill Protection Recommended Practice for Storage Tanks in Petroleum Facilities: Frequently Asked Questions (Part 2)

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During the past few months, we have fielded dozens of questions about the recently revised API RP 2350 recommended practice for overfill protection. This week, we are sharing some of the most frequently asked questions that we’ve received to help you understand this very complex topic. For more information about API 2350, please review last week’s blog post.

Frequently Asked Questions about API RP 2350

  • Question: Does API 2350 apply to tanks filled from trucks?

  • Answer: API 2350 limits itself to tanks filled via a pipeline or marine vessels. It does not include wheeled vessels such as trucks because they simply do not carry much product. API 2350 is specific to pipeline and marine vessels because the potential for devastating overflow is from sources that have a much higher capacity than a truck.

  • Question: How popular are the category 1, 2 and 3 tanks? Which category is the most popular?

  • Answer: For most companies, it is really about existing resources rather than tank type popularity. While most new tanks are likely to be a category 2 or category 3, the recommendation does leave room to categorize any existing tanks that are less automated and use them as fully- or semi-attended. This gives the owner/operator an opportunity to meet the specification, regardless of the type of equipment that they have on their tank.

    As owners/operators review their facilities, they need to look at the type of equipment that they currently have. To get to category 3, there will be additional equipment and personnel costs involved to automate and add devices; however, following the new recommended practices can help limit liability and costs if an incident occurs. Assessing these risks – and what the company can afford to do – will determine the category level of its tanks.

  • Question: Can I use radar gauges in tanks with an internal floating roof or only in tanks that have a fixed roof?

  • Answer: You can use radar under either condition because a non-contact radar device senses the position of the roof itself. If there is no floating roof, the radar will detect the fluid. Depending on the dielectric of the fluid, you can set up the radar transmitter to measure either the roof or the liquid to detect an overfill situation.

  • Question: Can I apply API 2350 recommended practices to tanks with flexible internal roofs that have pontoons?

  • Answer: Yes. Ultimately, the standard is based upon overfill protection. A floating or pontoon roof just changes the types of technologies that you should consider using. Radar technology may be a good choice, but mechanical devices such as a displacer switch can work because they are also activated by the floating roof.

  • Question: If proof testing shows that a system does not work and the operator fixes the valve or alarm operation, does this change the testing frequency (especially if the system fails a subsequent test)?

  • Answer: We would recommend increasing the testing frequency if you have a history of failed tests; however, API 2350 does not address proof testing in that much detail. It does specify the maximum intervals, but it is up to the owners/operators to institute additional testing if they think it is necessary. In a situation where you have had previous failures, it makes sense to increase the testing frequency until you again have enough confidence in the equipment to use the API 2350 testing intervals.

  • Question: My float switch has a push-to-test feature. Is this an acceptable high-level alarm switch?

  • Answer: Manufacturers added the push-to-test feature to many floats several years ago. This was done to activate or short out the relay, which would send a signal back to the control room or operator to indicate that there was a positional change.

    Unfortunately, many float switches today are magnetically coupled between the relay and the float and do not actually move the float during the push-to-test. As a result, when the float has any type of buildup around it – or any kind of malfunction that does not allow it to move properly – the push-to-test falsely indicates that the device is operating. The push-to-test feature is really only checking the positioning of the relay and the integrity of the wiring system back to the control room.

    To determine the validity of a push-to-test feature, you need to determine the type of float switch you have and how the push-to-test works (i.e., does it actually physically check the position or movement of the float). In reality, any type of self-testing device (or any device that has the capability to provide diagnostics) is a better choice for a high-level switch. This is especially true when you are dealing with critical levels because the self-diagnostics of these devices are more reliable than the push-to-test on a float switch that doesn’t actually test the integrity of the float.

  • Question: What are the wireless allowances outlined by API 2350?

  • Answer: API 2350 deals with safety and protection. Although wireless is becoming more popular, it is less reliable. As a result, wireless is forbidden in an overfill prevention system (OPS). Wireless will never be as reliable as a wired piece of equipment, so it makes sense that the recommended practices do not allow wireless in a safety system.

Next week, we will wrap up our series of frequently asked questions about API RP 2350. For more information about these new recommended practices, please view our recent API RP 2350 webinar.

Register to Attend Our API 2350 Webinar Now!

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