The recently revised API RP 2350 recommended practice for overfill protection has generated much discussion about tank level sensing. During the past two weeks, this blog has answered some of the most frequently asked questions we’ve received about using this standard to improve tank safety. This week, we’re wrapping up this blog series by answering a final set of questions about this complex topic.
Frequently Asked Questions about API RP 2350
- Question: Does API RP 2350 apply to refineries?
- Answer: Absolutely. API RP 2350 does not reference the location or the type of site, but it does define which storage tanks the standards apply to, including the size of the tank, how you fill the tank and how much the tank can hold.
- Question: Are any compact probes or sensors available that can sense the presence of a very small amount of fluid (i.e., a few cubic inches of liquid)?
- Answer: If you have a very small amount of fluid in a pipe or on top of a roof, an ultrasonic gap switch can detect it – and may work more efficiently than a mechanical device. Another option is an electronic sensor. Some non-contact radar devices may also be able to detect small amounts of fluid in some applications and installations.
- Question: What is the typical lifetime of a single-point, top-mount displacer switch?
- Answer: A displacer switch is extremely reliable; however, the lifetime is highly dependent upon regular maintenance as well as the type of application and how often the application activates it. Generally, you can expect a displacer level switch to last 20 years; however, we have seen some last as long as 50 years. In addition, you can greatly minimize device failure by using current maintenance recommendations and installing a proofer device.
- Question: My system consists of SIL 1-rated devices, including radar switches. Do I comply with the new API 2350 RP?
- Answer: Although having a high level of reliability is good, the components alone do not comply because API RP 2350 covers the overall system. You must also have procedures in place that relate to timing, tank categorization, processes and communication within your system to meet the intent of API RP 2350.
- Question: Can I still use my tuning fork and capacitance switches for an HH alarm?
- Answer: With high-high level alarms, the reliability of your switches is critical. If you can perform regular self-tests to ensure that the unit is operating properly, you can continue to use these devices in installations such as a fixed roof where fluid contacts the device. However, if you have a floating roof, these types of liquid sensing devices will not work on the roof itself. You will need to invest in a more advanced technology that can detect the roof as well as the liquid.
- Question: How accurate and reliable is radar transmitter technology?
- Answer: If you are looking for a radar system to measure the level, it depends on the type of radar, the measurement accuracy needed and whether the measurement involves a custody transfer situation.
For example, if you simply need a positional indication or approximate measurement (i.e., to measure level within a half inch or a few millimeters), a pulse burst radar transmitter is a good option. However, pulse burst technology is not as accurate as a frequency modulated continuous wave radar, which can measure level accurately within 1 millimeter or less and is more suitable for inventory tracking.