how do you feel about radar level gauge transmitters for process safety

[diat150]

in my experience, they dont work well in my field, which is oil and gas production.

ive worked with rosemount apex, rosemount 3300, k-tec mt2000, and k-tec mt5000, and all are prone to the same failure. spikes or dropoffs in the level, or just nonreaction to a change in level. its been a constant fight despite different models and manufacturers. next up is the new rosemount 5400 series.


I just wanted to get a feel for how reliable radars have been for you in your experience and field.

I would prefer using float based mechanical switch or float based level transmitters, but others seem to think radars are better for our application. the amount of failures and shutdowns we have had tell a different story.

I am ok with using it for process level control, they just dont seem tobe stable enough to handle he safety side of the process, which leads to many unneeded shutdowns.

 

[NOLA]

I would never consider using them in a safety application. This time last year, I was wrapping up the commissioning of a new offshore oil & gas platform that had over 15 Rosemount 3300 guided wave radar transmitters used for level control and Ktek magnetic float transmitters used for level safety. We were having a lot of problems with the radar transmitters going into alarm mode which causes the output signal to bounce back and forth between 0 mA and 24 mA, which was causing valves to slam open and closed. You can only imagine what would have happened if they were tied to the safety system. We are still not a 100% sure what is the cause of this, but it is probably a combination of scaling on the probe, emulsion layers, and foaming. When they are turned properly and working fine, they are great; I just don't like how they bounce when they see a change in the process. We ended up mapping the Kteks to the level controllers as an interim fix.

 

[danw]

I assume you're talking about using a point level switch as a high or low limit?

Our rule is to use a different technology for high/low limit switches than for the primary continuous level signal, so that the failure mode will not likely be the same.

Floats are simple and sweet, but subject to hanging if the medium isn't self-cleaning, so we also consider capacitance if the dialectric is high enough, or ultrasonic gap point level switches. Once in awhile one even ends up with DP as a back-up.

Condensation on radar antenna seems to be suspect for some of these freaky loss of signal situations.

 

[NOLA]

No, I am not talking about point level switches.

I am talking about using the radar transmitters for continuous level control and using the Ktek magnetic float transmitters for safety (HH, H, L, LL) shutdowns and alarms. The shutdown and alarm setpoints can be adjusted in the PLC via the HMI. Therefore, we are meeting the requirement of using separate technologies for safety and control.

Come to find out, the new Rosemount 5300 has a feature that allows you to set up to a 60 second delay before reacting to an error condition. This would alleviate the problem we are experiencing. It also has some other nice features such as the capability to dynamically adjust to changing dielectric properties.

 

[Mike Dyble]

We use Vega guided microwave in a safety application on liquid chlorine tank levels. But we also monitor tank weight, so we have two different technologies which contribute to the inputs to the ESD system, with 1oo2 voting. So high weight or high level stop filling.

They have been reliable, we havnt had any major problems. (Which is just as well as changing one involves empting a tank with up to 100t of chlorine in it, and then purging it).

 

[diat150]

I assume you're talking about using a point level switch as a high or low limit?

Our rule is to use a different technology for high/low limit switches than for the primary continuous level signal, so that the failure mode will not likely be the same.

Floats are simple and sweet, but subject to hanging if the medium isn't self-cleaning, so we also consider capacitance if the dialectric is high enough, or ultrasonic gap point level switches. Once in awhile one even ends up with DP as a back-up.

Condensation on radar antenna seems to be suspect for some of these freaky loss of signal situations.

what we have is two of the exact kind of radar next to each other, one for safety and one for process. they dont always screw up at the same time. the problem is we shut in a huge amount of production pretty regularly due to malfunction on radar gauges.

weve gotten alot of push back from the engineers on this so i was just wondering if it is just me that thinks radars are just not reliable enough to use as a safety device.