Improving Process Safety & Reliability by Understanding Machinery Health

– Holistic Approach Uses Standards-Compliant Solutions to Streamline Maintenance

Safety can’t wait. Ensuring that a plant’s staff and equipment are not at risk of accidents is the single most important thing any organisation can do to ensure long-term viability.

Whether the economy is good, and organisations have more resources to work with, or markets are down and demand has shrunk, allowing gaps and blind spots in safety systems means jeopardising safety and putting workers, the company’s most essential asset, at risk.

What many organisations fail to recognise is that safety does not exist in a vacuum. Some peace of mind is possible for plant managers simply by knowing that rotating equipment will shut down automatically when sensors detect a fault.

However, true plant safety can only be achieved when systems are well integrated and implemented in a way that makes them easy for staff to use.

Instead of focusing on individual pieces of equipment, organisations must examine how safety system upgrades can be performed holistically for long term-viability.

By planning for long-term implementation and use of safety system upgrades, plants can not only improve safety, but also improve reliability, all while saving money and streamlining future improvements.

A safety system example…

For a large food manufacturing company in the US Midwest, Emerson, was able to offer the perfect solution to implementing a safety system with the organisation’s future needs in mind.

The organisation was working with machinery health monitors that were no longer supported by the manufacturer. Moreover, knowing that the system was obsolete and needed to be replaced, maintenance crews had given up on maintaining a standardised maintenance strategy.

Because there was no corporate standard maintenance strategy, different plants operated systems very differently. One plant might have equipment measuring points that were non-existent at a plant in another state.

There was no guarantee that a variable that one set of technicians depended on would be measured at every plant in the organisation. Even instrumentation could vary from location to location.

The differences between plants were of particular concern for management because the organisation has a policy of moving experienced technicians between plants during outages.

It is not uncommon for half of the maintenance staff of a functioning plant to help out at another location during serious equipment failure. However, when these technicians travelled to other plants, their ability to help was hampered.

Many of the measurements and devices they had come to rely on at their home plant were not in place or functioning differently at the new location. As a result, the maintenance crew spent hours learning new ways to identify the problems rather than resolving the issues.

In addition to the lack of standardisation, the legacy monitors slowed integration with the plant’s modern DeltaV distributed control system. The traditional control system integration that the organisation had been using for its previous machinery monitors was non-intuitive and expensive.

Discovery and integration of monitors was complex, time consuming, and expensive. Data mapping was difficult and required regular maintenance, using up time that could have been spent more productively on other tasks.

Even when properly connected, the legacy monitors were very limited in the data they could report to the control system, leaving maintenance blind on many essential machinery health variables.

When the safety functions connected to milling equipment and wet process centrifuges needed an update, the organisation decided to adopt a best-practice approach to improving the company’s standard for safety (Figure 1).

This approach meant updating and improving all the designs for each safety function plants relied upon.

The organisation engaged vendors with a proven track record in best-practice safety systems. Because of its long history using DeltaV, the organisation contacted Emerson to evaluate the benefits of rolling out new safety equipment.

The organisation quickly learned that working with its control system vendor to develop a machinery health equipment solution offered significant benefits. Emerson provided best-in- class machinery health and safety monitoring equipment in the CSI 6500.

The vendor also helped develop an enterprise-wide machinery health and safety programme that standardised safety system equipment, processes, and features at all plant facilities.

In addition, the company gained a single point of contact for all of its machinery health devices and software, making implementation and support significantly easier.

Working together with Emerson subject matter experts, the organisation developed a plan to roll out a standardised machinery health and safety system to the entire fleet over the next 3 years.

By 2018, all legacy monitors will be gone, replaced by new equipment that can report far more detailed vibration data to the plant’s control system.

Plants throughout the organisation will no longer have to worry about spurious trips due to ageing monitors, and will have constant access to a wealth of information about the health of critical equipment.

At the end of the machinery health programme roll-out, all plants will function under a standardised machinery health initiative. The monitoring equipment and collected variables will be the same fro device to device, and from plant to plant, helping maintenance staff avoid having to re-invent the wheel for problem detection and diagnosis.

It will also allow the organisation to track problems fleet-wide, so the maintenance team can identify trends in machinery health issues and begin preventing rather than simply repairing many equipment problems.

Process Safety fast…

Maintenance teams no longer need to worry about integrating machinery health monitors with the organisation’s control system. By standardising control system and machinery health monitoring equipment under the umbrella of one vendor, the organisation gained access to Emerson’s easy three-step integration between machinery protection and the DeltaV, control system.

Safety system adds and changes that used to take days can now be completed in under an hour. Any communication issues between the monitors and the control system can be easily and quickly detected and diagnosed, without the need to untangle a complicated web of integration.

At the sites where roll-out is complete, technicians are already seeing stunning results. Using the software configurable interface for the CSI 6500, maintenance crews can make adjustments and tweaks as needed to critical equipment in the plant.

Now, when crews try new configurations to improve and optimise production, they can see immediate results and reports on the changes they make. The software provides a clear picture of what is happening with equipment at any given moment (Figure 2).

Technicians have even found unexpected benefits from upgrading monitoring equipment. Two separate plants immediately started seeing nuisance trips from thrust issues on start-up after implementing their new machinery health monitors.

Because previous devices didn’t register the trip, the maintenance teams knew that the problem had to be a result of the more sensitive monitoring available on the new devices.

After investigating the problem, technicians discovered that the vibration sensor was not mounted properly and was slamming against the bearing, tripping the system.

Not only were the sensors now sensitive enough to detect the issue, but standardisation across the fleet allowed multiple teams to work together to bring the problem under control.

Working with a trusted partner has opened up new opportunities for the organisation. The existing connectivity between the machinery health monitors and the DeltaV DCS simplifies the process for future safety system expansions.

The organisation is already evaluating implementation of a predictive maintenance package, so the current machinery health infrastructure upgrade has been designed with that future in mind.

Using standardisation as a guiding principle, the design and layout have been developed to make upgrading easier, with some power and wiring already in place. When the organisation decides to upgrade, it will be less expensive and simpler to install predictive maintenance options.

By increasing the capabilities of machinery health equipment and making standardisation across the organisation a priority, the members of the implementation team have set the company up for future successes.

The organisation can be confident that any equipment failures will be immediately addressed. They can also rest assured that any future upgrades, questions, or concerns can all be addressed from a single point of contact, making the system simpler to support, maintain, and upgrade.

Understanding key measurement types in online shutdown protection systems

It is important to understand some of the key measurement types in an online shutdown protection system. Not all assets will have all measurement types, but many will be common to multiple devices. As such, it is good to be familiar with all of them.

Shaft Vibration (relative)

This measurement type is always done on a fluid film sleeve bearing and is supplied using eddy current sensor technology.

Shaft Vibration (absolute)

This measurement type is always done on a fluid film sleeve bearing. Relative shaft vibration is

measured, and the absolute bearing housing vibration is measured using an accelerometer or velocity sensor along the same axis as the eddy current sensor.

Bearing Vibration

Bearing vibration readings are taken on both antifriction bearings and fluid film sleeve bearings. Accelerometers, piezoelectric based velocity sensors, and seismic, electrodynamic based velocity sensors are usually employed to measure the bearing or machine case overall absolute vibration.

Position Measurement

Position and expansion on shafts, bearing housings, and machine cases are measured using eddy current sensors on rotating machines.

Eccentricity

Shaft eccentricity is the dynamic movement of the outer shaft surface to the geometrical centre of the shaft (also called residual gap).

This measurement requires a tachometer phase reference to initiate the time series collection and the measurement consists of one complete shaft revolution measured with an eddy current sensor.

Phase

A tachometer is used to produce a pulse when a target passes it once per shaft revolution. This timing pulse can be used to provide a phase reference point for all the vibration measurements on a machine.

This allows phase comparisons of the multiple vibration measurements on a machine using two dimension visuals such as each bearing’s XY orbit data.

Differential Expansion

Differential expansion (relative expansion) is a measure of the change in the clearances between machine parts caused by thermal expansion or contraction. (e.g., rotor discs to turbine housing). The most common method to measure this effect is by using eddy current sensors.

Valve Position

Valve travel amount is used to determine whether a valve is open, partially open or closed. LVDT sensors have the long displacement measurement capability to measure valve position.

Speed Measurement (acceleration, direction, and more)

Speed measurements are usually collected by an eddy current sensor reading a pulse wheel or a gearwheel. The current speed in hertz is calculated by dividing the amount of pulses per second by the number of gear teeth on the wheel.

By having many pulses per revolution it’s possible to quickly determine if the asset speed is consistent, accelerating or decelerating.

Axial Position Protection

A fluid film sleeve oil ‘thrust’ bearing is designed to be the fixed bearing of a fixed/floating bearing pair. This bearing is expected to keep the shaft from wandering in the axial direction which will result in a catastrophic event when the clearances in a rotating machine such as a steam turbine disappear and high speed metal to metal contact of the rotor with the housing and seals occurs.

Process Variables

Because of the growing application of sophisticated and networked modern analysis and diagnostic online prediction and protection systems, it becomes increasingly easy and essential to capture process parameters and trend them along with the online prediction and protection analysis parameters to allow the visualisation of potential relationships between them.