Dear all

This is my first post at AMP so I hope I am using the correct forum.

My name is Claes Fredö and my company, Qring, works with troubleshooting such that we usually set up a multichannel system to record data 24/7 and leave it there for a duration of anything from hours to years depending on the problem. This methodology is very much the opposite of usual condition monitoring and aim at identifying and catching the occasional gremlin that pester a system, i.e. finding the needle in the haystack.

In addition, Qring tries to measure using a plethora of sensors as we find it more likely to believe a sighting when caught by two or more sensors of varying design. From time to time, the key piece of the puzzle may originate from understanding why a sensor misbehaves.

We are currently dealing with a pipe system that has a hanger that has failed a few times. The system is made up by a bunch of centrifugal and reciprocating pumps who share a pipe support.

Unfortunately, I am not able to share any data.

We measure 43ch vibration up to 1 kHz using accelerometers, relative position/orientation using a bunch of wire string sensors, mechanical stress using ordinary strain gauges configured in quarter bridges, temperature, pressure, pulsation using piezocables (http://qringtech.com/2014/01/2...o-measure-pulsation/) and summed current (L1+L2+L3+N+Ground) using Rogowski coils and ordinary inductive clamps. We do not measure summed current out of anything but convenience and use it as a quick and dirty way to troubleshoot things such as torsion vibration (http://qringtech.com/2017/05/2...sis-of-flue-gas-fan/ ).  

We find the highest mechanical load not to arise when any of the pumps are running. We find also that there is correlation between vibration and summed current.

After much scratching my head, signal validity checking and running the problem by a seasoned power electronics specialist - it appears that the peak stress load/vibration is caused by AC ground potential that cause AC current to redistribute between the three pipe systems at the shared pipe support where two supports are guided sliding and one is fix.

The physics is there and if I am correct in my understanding of the problem, AC current would act like an electromagnet at the sliding supports.

To clarify and define, the summed current that we measure does not really tell us the amount of current that runs through the piping as there is a ground cable located between our measurement position on the power cable and the pipe.

Digging into details, it appears to be something that emits short duration burst near 1 kHz. I base this on the fact that we sample up to 1 kHz, have anti folding filters on the instrumentation and as the Rogowski coils we use only measure up to 3 kHz.

AC and DC ground current is a common problem for piping. It is easy to find work safety instructions telling people to ground the pipe system before working on it. Also, ground problems and EDM is well known for bearings.

However, googling the matter as well as searching this forum, I find nothing written about piping, ground current and vibration. It appears to be an oddity, I suspect, not because of its nature but of the problem being multidisciplinary.

My question to the forum is - has anyone come across a similar problem for piping where ground potential or some other source?

At this time, my focus is whether someone has come across a similar problem rather than trying to identify the AC current source.

Sincerely

Claes

 

Original Post

I myself have not seen what you describe. My two cents, if something is breaking it is moving, if it is moving it is happening at a given frequency or it is a sudden burst of energy. Once you identify the frequency on the pipe support then you can work backwards to find what machine can cause the vibration?

Recommend you place a large coil spring in between the anchor source and pipe support, the spring will then absorb the energy

Dave

Hi Dave

Thx for reply. You are not alone in not having seen it before. Internet is virtually empty on the subject.

It appears to be intermittent bursts of current ~1 kHz. Finding the culrpit may take some work. Those in the know say it, e.g. might be a transformer that shuts on/off as the phases always are out of symmetry when turning on. In the same gist, it may be something major that shuts off where I expect the reverse.

I imagine a fix would be simple - just add a grounding cable between the pipes to unload the pipe support. 

FYI - I am currently working on an Xray machine where current also causes vibration.

The awful thing in finding an oddity once is that it keeps rearing its head once one know how to look for it. 

All the best

Claes

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