How New Level Monitoring Devices Help Improve Plant Safety

Related Vendors

DÜPERTHAL Sicherheitstechnik GmbH & Co. KG

Anton Paar GmbH

ProMinent GmbH

Emerson Process Management GmbH & Co. OHG

Emerson Process Management GmbH & Co.OHG

Proof-testing

Devices within safety instrumented systems in liquid level measurement applications must undergo regular proof-testing to make sure that they are operating to the required safety integrity level. Traditionally, device proof-testing not only takes a great deal of time and effort, but it also presents certain safety risks.

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If the test is carried out with the device still in the tank, it could involve having to change the tank level, if this is specified in the proof-test procedure. This is an inefficient, time-consuming task that requires the process to be stopped at inconvenient times, and creates the problem of disposing of the liquid used to perform the task. Proof-testing requirements could also involve technicians having to climb tanks, thereby increasing the risk of personal injury, especially when plants are in areas with extreme environments. Proof-testing can also be carried out by removing instruments from the tank and performing the test away from the process. However, this also has its dangers, as workers could potentially be exposed to vapour releases from the tanks when removing a device.

Given the safety risks involved, as well as the costs and the loss of plant productivity, proof-testing is something that plant managers would like to perform as infrequently as possible, while continuing to comply with the requirements for SIL 2-rated functions. Advances in today’s level measurement devices increase safety, efficiency and ease-of-use by enabling proof-testing to be performed remotely and in-process, without affecting tank operations. They also enable proof-testing to be performed less frequently. That’s because new generation devices’ undetected failures are so infrequent that proof-testing can easily be fitted into scheduled turnarounds, whether they are performed yearly, at intervals of five years, or possibly even longer.

The latest non-contacting radar transmitters, such as Emerson’s SIL 3-capable Rosemount 5408, can now be remotely proof-tested from the safety of a control room by following a simple instruction documented in the device’s safety manual. From a remote location, and without interrupting the process by changing the tank level, an operator can complete a comprehensive proof-test covering output circuitry, measurement electronics and wetted parts. This not only makes the proof-test much quicker but also safer, as it eliminates the need for workers to climb tanks and consequently keeps them away from danger.

Simulation Saves Time and Increases Process Availability

Vibrating fork level switches can be proof-tested remotely thanks to regulations relating to safety instrumented systems which permit the simulation of overfill conditions to activate the detector and generate an alarm signal. This simulation method not only saves time and increases process availability compared with traditional proof- testing procedures, but by enabling the test to be performed remotely it also increases safety by keeping workers off tanks and away from process liquids and gases.

Using this simulation method, the latest switches, such as Emerson’s Rosemount 2140, can now be proof-tested remotely simply by issuing a Hart command. The command puts the switch into a test mode, which cycles the output through wet, dry and fault states to check that the device is functioning as required.

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