Chemical Plant Wireless Sensor System

Root Cause Failure Analysis (RCFA) success at a Chemical Plant using high resolution wireless vibration sensors to inspect equipment with high overall vibration.

A commonly used wireless vibration sensor system was installed on a fan in a chemical plant. The system, part of a wireless instrumentation network, was only measuring overall values and some narrow bands. The system alerted the customer of an existing issue: overall vibration levels were high on a critical machine. As the only available information was the overall value, the customer had no way of knowing exactly how serious the problem was, or the cause of the problem.

SOLUTION

We installed the Wi-care™ vibration system on the machine. Installation and commissioning was completed in less than 15 minutes, and the first measurement results were received. Every 15 minutes, a spectrum was measured with Fmax of 4kHz and 6400 lines of resolution.

RESULTS

This was the trend plot after 4 hours:

It is obvious that the vibration level is fluctuating a lot. We employed the following methodology to find out why.

From the above plot, we select a measurement point when the machine was vibrating at 10mm/s (12PM), and analyse the spectrum.

The next measurement point we select is at 1:12PM, when the machine’s overall vibration is over 20mm/s.

When we compare both spectra, there is one difference – the speed. When the production increases, the speed of the fan increases from 1590RPM to 1665RPM and the vibration levels double

CONCLUSION

The imbalance value is high in both cases, so cleaning and field balancing are recommended. However, the fact that a small change in speed, has a major influence on the imbalance value, is an indication that the fan is also running close to it’s resonance frequency (critical speed).

Thanks to these results, the customer knows the root cause of the problem and can now plan action to solve it.

To obtain this information, Wi-care™ sensors were installed on the machine, and also powered a gateway in the neighbourhood. This installation took less than 15 minutes. Half a day later, this conclusion was produced. This proves once again that the Wi-care™ remote condition monitoring system is a Plug & Play system that provides high resolution data and high accuracy in determination of fault.

Ventilation Fan Predictive Maintenance System

A predictive maintenance department at a chemical plant was alarmed by a sudden increase in overall vibration values of their Wi-care™ system, installed on a ventilation fan for their production units.

The spectrum below is the spectrum at the moment the highest amplitude was reached.

The high peak shown above is at 8 orders or 380Hz with an amplitude of 7.6 mm/s.

The following cascade plot shows clearly that all the increased energy is purely coming from this 8 order peak.

What is the reason for this 8 order peak? This is a fan with 8 blades. 8 orders is the blade pass frequency.

This is was a fan that needs cleaning on a regular basis. The cleaning is done over a weekend with water under pressure. During the cleaning procedure, maintenance personnel must open a fan at the bottom of the fan house to allow the cleaning water to leave the installation.

In this particular case, they forgot to open the fan, and the fan house was full with water when the fan was started. The fan turned on, and acted as a pump. This was identified as a result of the alarm generated by the Wi-care™ condition monitoring system.

After opening the valve and removing the water, the fan was running again in smooth conditions.

The following cascade plot (3D Waterfall) shows the spectrum before, during and after.

Where there has been a significant, immediate change in operating parameters, overall vibration serves as a useful alarm system that calls for further investigation.

Utilising condition monitoring technology that includes both overall vibration alarms and high-resolution vibration spectrum analysis, ensures that the cause of the alarm can be quickly and accurately identified, and specific follow-up actions can be scheduled.

Ball Mill Gearbox Fault Identified Before Failure

A Wi-care™ wireless condition monitoring system was installed to monitor a Ball Mill gearbox and associated 1MW electrical drive that were suspected to be faulty at a well-established Cement Plant operating at full capacity.

The customer requested technical support after a suspected increase in the vibration level of the equipment. A Wi-care™ wireless condition monitoring system was installed to enable in-depth and concise monitoring and diagnosis of the vibration on the complete assembly.

SOLUTION

The Wi-care™ system was set up on the gearbox and the electrical drive in minutes using magnetic locators to cover classical vibration directions, vertical, horizontal and axial planes. Note on the right side of the equipment (pictured above) the Wi-care™ speed sensor directly measuring with a key-phasor on the shaft.

Standard spectrum collected via Wi-care™ on the vertical axis. Display in speed units. The dominant frequency appears at 373.9Hz and it’s harmonics.

When zooming in on 373.9Hz appears modulation at 5Hz. The amplitude is close to 4mm/s RMS.

Following on from inspection of the drawings and data sheets, we can find the gearbox specifications and calculate theoretical fault frequencies.

RESULTS

Calculated gear mesh frequency of 373.71Hz and it’s harmonics match the measured frequency of 373.9Hz. Detected 5Hz modulation is linked to a ring defect (5.01 calculated). Amplitude trend indicates a 100% growth over a few days.

Based on recommendations via Wi-care™ measurements, the decision was taken by the customer to initiate maintenance inspection. The root cause of the gear defect was excessive looseness in the gear assembly due to structural cracks. The customer was then able to take immediate action to resolve the problem.

Paper machine – high temperature application

Environmental conditions are tough because certain areas will have a humidity of near 100% and temperatures reaching 130°C.

In general, paper machines have a total length between 100 and 200 metres and produce paper between 6 and 10 metres wide. Some can produce as much as 2km of paper per minute. In other words, 120km of paper per hour.

The press section and drying section are equipped with hundreds of large roller bearings, each of them critical to the operation of the machine. Because of the criticality of the bearings, vibration monitoring programs using periodic route-based measurements are very common in the paper industry.

Although online monitoring solutions are becoming more common, both hardware and installation costs of these systems often remain an obstacle. As a result, one expects periodic vibration measurements will remain the method of choice in many cases, and for many years to come.

Due to the sheer amount of bearings and the working conditions, monitoring programs will continuously provide for the follow up of the progression of defective bearings, trying to estimate the optimal timing for intervention. For paper plants, it is important to limit the amount of planned maintenance stops to a minimum and certainly to avoid additional unplanned stops for urgent bearing replacements. So, often the maintenance responsible will be very well aware of a severe bearing defect but will want to run until the next scheduled production stop, if unacceptable risks can be avoided.

SOLUTION

The following example is a case study where Wi-care™ monitoring system was requested for a defective bearing, to intensively follow up the progression of the defect, allowing to support the decision if it could continue to run through the upcoming weekend, providing a less costly opportunity to replace the bearing.

As always, installation, implementation and commissioning of the Wi-care™ system was completed in less than 15 minutes. Because of the difficult environmental conditions (temperature and humidity), a solution with the high temperature accelerometer with integrated cable and a separate Wi-care™ transmitter was selected. The gateway was installed in the repair shop nearby.

RESULTS

Below is a trend plot of overall vibration amplitude, measured from Friday until Monday (when the machine was stopped).

The amplitudes are increasing slowly and consistently. The blue circle indicates a period of a couple of hours, where production speed was lowered and amplitudes dropped accordingly. The red circle shows a short production stop, because of a paper break, a common event for most paper production machines.

Below plot shows the spectrum of the damaged bearing, with the classic pattern of an inner race defect, with strong presence of running speed sidebands.

CONCLUSION

Because of the gradual, but certainly not exponentially increasing amplitudes, and by being familiar with the amplitudes that similar bearing defects exhibited in the past, it was decided to continue to run through the weekend. Stopping the machine after the weekend significantly lowered the cost of the repair, while permanently and remotely monitoring the defect made this possible without taking unacceptable risks.

Included are two pictures illustrating the severely damaged bearing, encountered during the repair. Also, the 3D waterfall graph comparing the vibration spectra before and after the repair.

Mill Discharge Lubrication Issue

Bureau Veritas is a world leader in testing, inspection and certification services.

Global Pumps provided a trial remote condition monitoring system for the Bureau Veritas Minerals geoanalytical laboratory in Adelaide, to assist in ensuring the success of a critical project involving testing and analysis of mineral resources for a mining company. The project ran for 6 weeks with two rotating 12 hour shifts.

The Issue

On 27 June 2017 the mill and mill discharge pump began to experience a fault. This was immediately detected by the attached sensor which generated a vibration alert in the condition monitoring system. The alert was sent by email to Global Pumps.

Alerts and Notifications

The email was immediately followed up by a phone call from John at Global Pumps with warning of the vibration alert to David Millan at Bureau Veritas. While the pump was being inspected, John called again warning of a high temperature alert on the pump.

Immediate Actions

After the second phone call from John, the pump was immediately inspected which revealed that it was running hot. Action was taken to grease the pump bearings and the temperature immediately decreased, The pump casing was then monitored throughout the day with no further problems.

Preventative actions

The condition monitoring sensor on the mill discharge pump worked perfectly and the initial alerts were followed up by the supplier with phone calls to warn of impending trouble. Previously this event would have gone unnoticed and the pump would run to failure. This would result in ceased operations, with high cost of downtime and associated labour and repair costs, and the project would have halted completely.

“The Global conditioning monitoring solution enabled us to avoid a critical equipment failure that would have caused a total shutdown in our operations.”

David Millin
Project Supervisor – Integrated Pilot Plant, Bureau Veritas Australia Pty Ltd