Kraig Simpson
Vice President of Global Technology Solutions
Rotating Machinery Services (RMS)
He holds a B.S. in Mechanical Engineering from Mississippi State University. Prior to RMS, Kraig worked for ExxonMobil for 10 years.His professional experience has been primarily focused on turnaround, maintenance, and project support. Much of his experience is related to leveraging technology and innovative solutions to reinvent maintenance techniques for turbomachinery. He has applied the virtual assembly philosophy for numerous applications including turbomachinery overhauls and brownfield project execution. He has previously presented case studies and tutorials
on the topic of virtual assembly at various industry conferences, including TPS and ATPS
Josh Cowart
Director of Global Technology Solutions
Rotating Machinery Services (RMS)
Josh began his career as a machinist at ExxonMobil and advanced through various roles, eventually becoming the Lead Turnaround Planner for the Baton Rouge, LA Chemical Plant. Josh planned and executed more than 50 turbomachinery overhauls throughout his career, primarily in ethylene process gas and refrigeration services. Josh traveled to ExxonMobil sites globally to share knowledge, review turnaround plans, and provide innovative solutions. He helped pioneer virtual assembly for both turbomachinery and static equipment applications. In his current role, Josh oversees both Field Service and Metrology personnel.
Adam Walker
Senior Maintenance and Reliability Manager
Westlake Chemical (Lake Charles)
He holds a B.S. in Mechanical Engineering from Louisiana State University. Adam started his career as a Project Engineer for PPG. He also held various engineering and maintenance roles at Axiall Corporation (acquired by Westlake Chemical in 2016). Prior to his current role, Adam was the Reliability Team Leader at LyondellBasell. In his current role, Adam oversees maintenance and reliability efforts, most notably for a 2025 ethylene turnaround.
Corey Fenetz
Reliability Superintended
Rotating Equipment at Westlake Chemical
applying his expertise to ensure optimal performance and longevity of critical rotating machinery. He earned his Bachelor’s degree and has built a strong career in industrial reliability and maintenance. At Westlake, Corey leads teams focused on preventive and predictive strategies, equipment uptime, and safety, leveraging his engineering background to drive operational excellence in petrochemical plant maintenance
Benjamin Gatte
Reliability Engineer
Westlake Chemical
He holds a B.S. in Mechanical Engineering from McNeese State University. In his current role, Ben focuses on improving equipment performance and operational efficiency through preventative maintenance and data-driven strategies. His background includes a strong foundation in mechanical systems, gained through both academic training and hands-on industrial experience in the petrochemical sector
ABSTRACT
Anyone involved in planning and executing turbomachinery turnarounds understands the importance of developing a solid plan and having an experienced team to execute that plan. Though there have been many advancements throughout the years positively impacting turnaround safety and quality, the execution duration of a turbomachinery overhaul has been relatively unchanged. Over the last decade, however, vast improvements in technology have enabled engineers and technicians to reimagine how quickly a turbomachine can be overhauled.
Advanced precision metrology is one of the tools being used to reduce turbomachinery downtime durations by up to 75%, while improving quality and safety [1]. Turbomachinery can be virtually assembled to identify and address assembly issues prior to physical assembly and eliminates traditional, manual, and iterative techniques. Internal clearances and component positioning can be optimized virtually, enabling the precise physical assembly of spare components. Virtual assembly allows us to reimagine the execution sequence for overhauling turbomachinery, enabling the rotor, bearings, and seals to be worked in parallel to the compressor casing, diaphragms, and other stationary components. Virtual assembly enables an innovative, modular approach to maintenance.
However, there is a significant amount of detailed planning required to successfully utilize precision metrology to make real-time decisions. Detailed pre-turnaround planning is necessary to optimize the execution sequence for turbomachinery overhauls, especially when there are multiple equipment bodies needing to be worked in parallel. By integrating precision metrology with large area laser scanning, maintenance digital twins can be developed, enabling a realistic simulation down to a very granular level.
Maintenance digital twins can highlight special tooling, rigging plans for complex lifts, and technical hold points for taking critical measurements. These detailed simulations can be leveraged for training engineers, technicians, and supervision prior to a downtime to ensure everyone understands the equipment layout, pieces and parts within the machine, and methods for overhauling the equipment. Digital twins can also be used for training new employees that may not have an opportunity to see the equipment open for many years and for knowledge retention of more experienced employees, capturing and incorporating their vast experience collected throughout their careers.
Virtual assembly and maintenance digital twins enable a novel approach when overhauling turbomachinery. Downtimes in this industry typically result in huge monetary losses, costing some customers millions of dollars per day. By leveraging advanced technology, assembly issues can be identified in advance of causing schedule delays, and execution sequences can be optimized, shifting the paradigm for how maintenance has been conducted for the past 75+ years. Leveraging precision metrology and scanning, complete digital replicas are created for each machine down to the smallest components. This data is then stored for future downtimes, driving even more efficiencies and insights for those subsequent outages.
This tutorial addresses how precision metrology, virtual assembly, and maintenance digital twins are changing the way the industry plans and executes turnarounds. An example ethylene train is considered in this tutorial with emphasis on all typical phases from start to finish, involving pre-turnaround, turnaround, and post-turnaround activities. Technology integration is discussed in detail to explain how such a vast reduction in execution duration is achieved on a complex, large, multi-body train
INTRODUCTION
Turbomachinery is intricately designed for precision machined components to perfectly fit together with very tight tolerances. Generally,
when the machines are first assembled in a factory, technicians can work slowly and meticulously in a low-stress, temperature-controlled environment. The complex machines are assembled and shipped to customers where they will sometimes operate nonstop for a decade or more before requiring maintenance. Great advancements have been made to improve the reliability of these machines and to extend maintenance intervals. This makes it difficult to justify purchasing a complete spare machine for many applications. Therefore, when a turbomachine requires maintenance, many operators are required to partially or entirely halt production. In some industries, production losses can equate to millions of dollars per day
Unlike initially assembling the turbomachine in a low-stress environment on a non-expedited basis, maintenance is often conducted in high-stress environments with numerous crafts working around the clock. Operators typically align maintenance schedules for entire facilities to minimize disruptions to production and therefore lump most turbomachinery and static equipment maintenance together within a compressed duration. These planned maintenance windows are commonly known throughout many industries as turnarounds. Due to the size and complexity of the turnarounds, operators are often required to halt production for weeks or even months to facilitate all planned maintenance activities. Hundreds of employees and contractors clean, repair, and replace equipment. In addition to the
production losses, this also represents a notable safety risk.
During a typical centrifugal compressor overhaul, numerous lifting activities are executed. Traditional assembly generally requires multiple iterations of lifting components such as the rotor and upper casing to take critical measurements and make fine adjustments. In addition to these lifting activities taking valuable time, they also require numerous resources, pose safety risks for employees, and increase the probability of damaging a critical component during the lifting process. In many instances, other maintenance activities in the surrounding area are halted while critical lifts are occurring to minimize risks to the associated safety hazards.
Operators have invested substantial time, money, and resources to explore ways to minimize turnaround durations, reduce personnel safety exposure, and improve the probability of a turnaround being executed without any quality incidents. Regardless of turnaround size and complexity, a comprehensive planning effort is one of the primary operator investments. These planning efforts can comprise of numerous personnel ranging from Operations, Engineers, Maintenance Specialists, Original Equipment Manufacturers (OEMs), third party service providers, and contractors.
All planning efforts must be integrated across all disciplines. During a typical turnaround, there are many other functions requiring integrated planning efforts in addition to planning to overhaul the turbomachinery. Operations must develop a plan to rid the system of process gas. Valves must be functional, and blinds must be inserted to ensure proper isolation. Instrument Technicians develop plans to disconnect, repair, and replace critical instrumentation. Electrical Engineers build plans to isolate and inspect electric motors, often executing associated maintenance or upgrades during the same turnaround window. Heat exchangers must be cleaned and inspected. Vessels and piping sections require repairs. Controls improvements are implemented to upgrade critical safety systems. Projects are executed to upgrade obsolete equipment or to meet new environmental regulations. Methods of transporting large equipment must be considered along with crane rental. Temporary facilities are established to accommodate hundreds of contract workers.
Traditional turnaround planning methodologies, such as those outlined by Rudisel and colleagues [2], established a structured framework for managing mechanical overhauls through meticulous scheduling, scope control, and contractor integration. These principles remain relevant; however, the industry has reached a turning point where planning is no longer constrained to static documentation and sequential tasking.The integration of precision metrology and maintenance digital twins enables dynamic, simulation-based planning that allows teams to virtually execute work packages, validate clearances, model rigging activities, and preassemble components in parallel. This paper builds upon those foundational practices by demonstrating how technology is redefining not just how work is tracked, but how it is conceived and executed in the first place.
In many instances, the work scope for turbomachinery sets the overall duration for the turnaround due to the complexity of cleaning,inspecting, and assembling new or spare internals and achieving the necessary, intricate operating clearances. Fortunately, advancements in technology have enabled significant duration reductions associated with many of these tasks. Precision metrology can be used to digitally map spare parts and internal stationary components, allowing engineers to evaluate how these components will precisely fit together and to make necessary adjustments prior to physically assembling pieces and parts. This ensures the parts fit together the very first time and eliminates time-consuming, iterative measurement techniques. This virtual assembly process significantly reduces the number of necessary lifting activities and minimizes high risk activities associated with both safety and quality events.
Though using precision metrology for virtual assembly during turnarounds can enable tasks to be completed more efficiently than traditional methods, the process requires significant technical forethought. Users should understand exactly what measurements to capture, and the data analysis process should be well understood. Engineers and Technicians will develop detailed measurement plans in advance of turnarounds, ensuring alignment and efficient workflow during the event. It can sometimes be challenging to envision how measurements will be taken and then virtually combined in software with other components for analysis. This is where a visual replica or maintenance digital twin can be extremely valuable. Data capture and analysis can be visually represented in detail. These digital twins can include every aspect of a turbomachinery overhaul, including sequence of events, special tooling, and complex rigging
and lifting. A maintenance digital twin can be an invaluable tool for training engineers, technicians, and contractors prior to turnarounds and can be leveraged for many years after a turnaround for training personnel. These digital twins can also be updated post-turnaround to include learnings and optimization efforts for future outages.
This tutorial builds upon the 2024 Turbomachinery & Pump Symposium manuscript titled “Transforming Maintenance Using Virtual Assembly” [1], which introduced the foundational principles of precision metrology and virtual assembly in turbomachinery overhauls. While that work established baseline workflows and demonstrated proof-of-concept through individual compressor and turbine examples, the current paper expands the discussion significantly by focusing on full-train integration and execution. This includes advanced case studies such as a multi-body ethylene train turnaround involving equipment from multiple OEMs, with no OEM oversight, and the deployment of a detailed maintenance digital twin. The paper further explores the application of digital twins for training, planning, and execution. The previous paper introduced precision metrology hardware and measurement techniques, while providing details and results associated with two independent case studies. This manuscript further explores virtual assembly capability and emphasizes systems-level adoption, integrated scheduling, field/shop synchronization, and provides a central focus on maintenance
digital twins. Additionally, the results now quantify turnaround duration reductions through validated case metrics, offering new insights into repeatability, risk mitigation, and workforce development.
VIRTUAL ASSEMBLY
Laser scanning and portable metrology tools have advanced tremendously over the last decade. Though most of these tools were initially designed for controlled shop environments, recent advancements in portability and reliability of the devices are enabling flexibility. An extraordinary amount of detail and data can be captured in a matter of minutes. When properly applied with experienced personnel, these tools enable decisions to be made much faster than historically. These devices can capture data with an accuracy of less than 0.001” in most environments [3]. The high level of accuracy and portability introduces many unique opportunities to leverage these tools during turnarounds, even in field environments.
Figure 1. Precision Metrology Hardware used to Probe Centrifugal Compressor Rotor
Diaphragm Alignment using Virtual Bearing Centerline
One of the more basic ways to use precision metrology is for simple alignment purposes. Figure 2 shows an example of checking bearing and seal bore alignment with diaphragms. This involves probing or scanning machined surfaces for bearing and seal journals in a casing along with each diaphragm bore. A datum is established along the bearing journals, and then the centerline of all other measured bores is compared to this datum. This allows technicians to make physical adjustments in a field or shop environment to ensure proper concentricity throughout the machine. A laser tracker can be attached to a magnetic base mated to a casing split line. Once the datum is established, a measurement probe can be used to quickly probe the bore of a diaphragm each time an adjustment to its position is made.
Real-time monitoring of positional changes is also possible using fixed points for monitoring via a “watch window” in the software. For instance, if a diaphragm centerline is 0.010” low and 0.014” to the right relative to the bearing centerline (datum), the diaphragm position can be physically adjusted with the oversight of a laser tracker and metrology software monitoring movement until the proper diaphragm position is achieved. The traditional method for executing this same task involves placing a mandrel in the bearings of the machine and rotating it with a dial indicator attached. Measurements are collected at various intervals as the mandrel is rotated. Though this has been an acceptable solution for decades, it involves designing, fabricating, transporting, and lifting a mandrel. These costly and timeconsuming tasks are eliminated using precision metrology. In this application, precision metrology is a much more affordable and quick
method for internal alignment.
Diaphragm Alignment using Virtual Spare Rotor
For larger turbines without specific guidance from the OEM for setting diaphragms, it may be necessary to take the use of metrology a step further. Gravity can cause larger rotors to sag substantially in between bearings. The spare rotor can be scanned and probed, typically prior to a planned turnaround. Once the digital replica is created, the rotor can be virtually overlaid into the turbine casing during the turnaround. The same steps described in the previous example are completed to establish bearing centerline in the turbine casing. The rotor is then virtually placed within the same environment and aligned with the bearing journals. When probing the diaphragm bores to establish positions, the comparison is now performed against the rotor centerline at that given axial location within the casing. In other words, in the previous example, the bearing centerline was assumed to be a straight line for aligning diaphragms. In the case of the larger machine, the diaphragms are aligned with respect to the actual rotor geometry in its static position between bearings. This generally aligns with OEM guidance for aligning diaphragms with larger rotors or mandrels, ensuring that diaphragms are properly positioned with appropriate interstage seal clearance during startup and through operation.
Figure 2. Steam Turbine Virtual Assembly – Diaphragm Alignment
Radial and Axial Virtual Clearance Checks
In addition to supporting bore and diaphragm alignment and concentricity checks, precision metrology can be further utilized to evaluate critical internal clearances. In the above example, the steam turbine rotor was scanned and probed prior to the turnaround. This means that all critical radial and axial geometry was digitally mapped. During the turnaround, with the rotor virtually overlaid into the bearing journals, the interstage packing/seals can be scanned and probed along with all other critical geometry, such as the leading/trailing edge of stationary diaphragms and blade tip radial surfaces. During this detailed overlay, it is even more critical that the rotor not only be properly aligned radially within the bearings but also be virtually positioned in the appropriate axial location. There are generally instructions provided from the OEM inclusive to cross-sectional assembly drawings stating which axial geometry should be used to correctly position the rotor axially. With a proper measurement plan, technicians can determine in real-time all axial and radial clearances between rotating and stationary components, highlighting areas of concern in which a measurement is out-of-tolerance. When executed correctly, this level of virtual assembly can provide substantial time savings and eliminate various lifting activities.
Figure 3. Steam Turbine Virtual Assembly
Traditionally (without precision metrology), the spare rotor is physically installed into the casing. Scotch tape of a known thickness is often positioned at various locations along each set of stationary seals. The rotor is physically installed into the casing and then removed.If the scotch tape did not make obvious contact with the rotor, additional layers of tape are applied to increase the thickness. This iterative process involves lifting the rotor in and out of the casing until the rotor contacts the tape. Micrometers are used to determine the total thickness of the tape, which represents the approximate radial clearance at that location. Lead wire can be used in conjunction with or in lieu of tape. The same concept is applied but typically takes less iterations by intentionally placing lead wire that is larger than the expected clearance and then measuring the actual clearance after the rotor has been installed and removed. This process is typically repeated for upper half seal clearances, requiring upper half diaphragms to be installed and removed. Virtual assembly eliminates this
time-consuming process for both lower and upper half clearances while providing higher quality data than traditional measurement techniques. In some cases, a diaphragm or rotor stage may be significantly out-of-tolerance, causing the rotating and stationary components to make contact when lowering the rotor into position. This could result in damage and delays to the turnaround. Virtual assembly greatly reduces the probability of such an incidence occurring.
Pre-Assembled Rotor
For some applications, such as a horizontally split centrifugal compressor, virtual assembly creates a unique opportunity for parallel work activities. As with the previous steam turbine example, measuring interstage seal clearances traditionally (without applying virtual assembly) requires an iterative process of lifting the rotor in and out of the lower half casing to conduct measurements using scotch tape or lead. The upper half casing is also lifted onto the lower half and then removed to subsequently measure upper half seal clearances. Once proper clearances are established, a traditional overhaul requires sequential assembly of the rotor, oil or dry gas seals, bearings, and finally the coupling hub. By leveraging virtual assembly, measuring and establishing interstage seal clearances in the upper and lower half casings can take place concurrently to assembling the spare rotor with seals, bearings, and coupling hub.
Figure 4. Centrifugal Compressor Rotor Scan
For a typical horizontally split centrifugal compressor, the spare rotor can be scanned and probed prior to the outage. During the outage, once the service rotor assembly is removed from the casing and diaphragms have been removed for cleaning and reinstalled, the critical geometry of stationary components can be scanned and probed. At a minimum, these efforts include digitally mapping bearing journals, thrust bearing housing axial fits, seal housing axial fits, and diaphragm discharge gas paths. Capturing this data allows a separate work crew to begin assembling the spare rotor. Within the metrology software, technicians virtually overlay the spare rotor into its optimal running position, virtually setting the rotor in the proper radial position within the bearing journals and aligning impeller to diaphragm discharge gas paths for optimal operating efficiency.
Figure 5. Centrifugal Compressor Stationary Fit Scan
The work crew will then physically assemble seal housings onto the spare rotor, positioning them at the correct axial locations that match the lower half casing geometry. Before proceeding with seal installation, engineers will evaluate each seal housing position relative to rotor position and determine if proper seal assembly can occur or if further axial adjustment of rotor position is necessary to accommodate the particular seal design. Oil or dry gas seals are then installed and locked into place with the seal housings temporarily supported on the rotor or using some other support fixture. Bearing assemblies are then installed. The exact sequence and assembly procedure is dependent on the compressor design. For compressor designs featuring integral bearing housings, radial bearings may need to be temporarily supported on the spare rotor.
For designs featuring external bearing housings that bolt to the seal housings, these can be assembled to the seal housings along with temporary supports. Once radial bearings are installed, the thrust disc is installed on the thrust end. Since the thrust bearing housing axial fits were scanned and probed inside the casing, the thrust bearing housing location relative to the spare rotor position can be verified to ensure the thrust disc is positioned at the correct location within the bearing housing to achieve the desired axial rotor position. Active and inactive thrust bearings are assembled to the appropriate thickness to maintain this position while accounting for the necessary thrust bearing clearance. For some compressor designs, vibration instruments can be installed in the bearing housings at this time. Bearing thermocouples can be checked to ensure they are functioning properly. Finally, the coupling hub(s) can be installed onto the spare rotor.
Figure 6. Centrifugal Compressor Spare Rotor Assembled with Seals, Bearings, and Coupling Hub
In this example, the entire rotor is assembled outside of the compressor casing ideally in a controlled shop environment. In parallel, a separate work crew is scanning and probing all interstage seals and making the necessary modifications to achieve appropriate clearances. Once the spare rotor is fully assembled and the interstage seal clearances virtually verified, the assembled rotor is lifted into position. The axial rotor position can be easily verified, interstage seals can be spot checked using feeler gauges, and typical thrust and lift checks can be conducted to qualify the final build. In this example, virtual assembly enabled parallel work activities and eliminated time-consuming lifting activities associated with typical assembly methods. Using this work method has shown to reduce durations for overhauling horizontally split compressors anywhere from 50-75% while minimizing exposure to safety and quality incidents associated with traditional work methods [1].
Figure 7. Centrifugal Compressor Assembled Spare Rotor Installation into Casing
The Necessity of Detailed Planning
As with any turnaround, there must be emphasis on detailed planning for the mentioned examples to be successful. In addition to the typical challenges and complexities of turnaround scheduling, managing logistics, and determining manpower, virtual assembly requires a special skillset that is not yet widely adopted throughout the turbomachinery industry. Teams must be equipped with experienced metrology technicians who are also competent with turbomachinery design and maintenance. Engineers assist with developing execution plans prior to turnarounds, taking into consideration machine design, operating context, maintenance history, and work scope.
Depending on what information should be collected, this team works together to develop an optimal schedule and considers where and when to apply precision metrology and virtual assembly. Metrology technicians build detailed measurement plans in metrology software to speed up the data collection and analysis process. Advanced quality control steps must be introduced throughout the measurement process to maintain proper equipment calibration and to ensure the desired accuracy is maintained. Engineers are required to review the data to ensure the results make sense and to give the final approval to proceed.
These detailed planning efforts require allotting time for the right resources to be engaged well in advance of a turnaround, typically at least six months. However, dedicating highly technical resources to a specific planning and execution effort can be challenging, as these resources are typically scarce and highly valuable to support other areas of operation. This is another area in which technology is enabling planning and execution models to be transformed.
Rather than being reliant and constrained to certain specialized personnel overseeing every complex work activity, maintenance digital twins enable critical and complex knowledge to be transferred effectively to less experienced resources. Maintenance digital twins ultimately increase the probability of success by equipping team members with an advanced understanding of specific tasks
MAINTENANCE DIGITAL TWIN
The term digital twin is broadly used and varies immensely across various industries. In general, a digital twin is a virtual representation of a physical asset or facility. These virtually replicated environments are typically connected to real-time data, such as operational or maintenance data. Digital twins enable users to determine how certain tasks will be conducted or respond in a replicated environment. This provides key insights for training personnel and help optimize critical operational or maintenance tasks. For the purposes of this paper, the term digital twin will be used to describe a virtual environment in which turbomachinery maintenance is replicated for the purpose of training and guiding personnel through the execution of a turnaround. This will be described as a maintenance digital twin. In this example, there is no integration to operational data. However, a self-contained schedule is integrated and monitored throughout the digital twin so that all users are updated with progress and status in real-time
Simple Digital Twin Examples Developed for Training Personnel
To develop the digital twin, a three-dimensional model of the equipment is first developed. Most OEMs have already created these models, especially for equipment designed and fabricated over the last two decades. Figure 8 shows a simple example of an oil free screw compressor in a generic shop environment. In this example, the intent is to train personnel on the basic configuration of the machine along with showing the typical disassembly and assembly steps. Personnel can explore the individual parts that make up the assembly by removing or hiding other components.
Figure 8. Oil Free Screw Digital Twin
Once the digital twin is developed, it can be easily modified for other work scopes. The generic shop environment can also be replaced with a virtual environment of an actual facility or even a field environment. This same concept is easily applied across a plethora of other types of turbomachinery applications. Figure 9 shows a hot gas expander that was developed to train personnel on some of the
sub-assemblies.
Figure 9. Hot Gas Expander Digital Twin
Multiple-Body Digital Twin – Field and Shop Environments
In some applications, it may be beneficial to develop the digital twin inclusive of the actual working environment. Visually replicatingspacing constraints, logistical challenges, and critical rigging and lifting activities using the onsite overhead crane can be very valuable to a planning and execution team. Figure 10 shows a digital twin of a multi-body ethylene train, consisting of a steam turbine driving three horizontally split centrifugal compressors. In this example, the actual working environment is included. The planned work scope consists of overhauling all bodies, including rotor swaps, diaphragm cleaning, and seal and bearing replacement. However, the steam turbine and compressors have different OEMs, and the train has been in operation for several decades. The turnaround was planned and executed by a third-party service provider with no OEM involvement. Therefore, no three-dimensional models were available. Applications such as this require a much more involved process for developing the digital twin.
Figure 10. Ethylene Train Digital Twin
First, each turbomachine is three-dimensionally modeled using CAD software. This is typically done using a combination of laser scanning and precision metrology, and by leveraging cross-sectional assembly drawings. Previous turnaround pictures and reports can also be helpful. One scenario is for the machine to be out of service and completely or partially disassembled. This enables the use of precision metrology and laser scanning to capture most of the information needed to build a CAD model. In many applications, however, this is not feasible, especially when planning for an upcoming turnaround with the unit in operation. In this instance, it may be possible to use laser scanning and precision metrology on the external machine bodies. This enables the casing and external features to be modeled in CAD. Spare parts are sometimes available for scanning, such as the spare rotor. This can be helpful when completing the model of the rotor and mating internal components. However, many of the components, such as diaphragms, will likely require modeling using the cross-sectional assembly drawings. There are typically some dimensions on general arrangement or cross-sectional drawings that can be used for approximating the size of internal components. For this digital twin, the exact dimensions and even certain geometry do not necessarily need to be included in the modeling effort. The purpose of this digital twin is to train and guide users through maintenance activities. For example, the exact vane geometry or flow path within the diaphragms are irrelevant for creating a visual representation of how to measure interstage labyrinth seal clearances. However, if there are unique features within a machine critical for executing certain tasks, pictures may be helpful in modeling a generic representation along with text callouts within the digital twin
Figure 11. Centrifugal Compressor Digital Twin Explaining Virtual Assembly Task
To include the actual field or shop environment within the digital twin, the environment must typically be laser scanned using a terrestrial or large area scanner. Sometimes hundreds of scans are necessary around a particular unit to create a complete representation of the area. For the ethylene train example, scans were conducted on the elevated platform where the machines were operating and at ground level to capture the overhead crane bay, oil facilities, and auxiliary systems. It is possible for these scans to be processed and converted for importing into digital twin environments. However, a scanned environment cannot be animated. In other words, scanning the bridge crane above the ethylene train is not enough to create animated steps showing the crane traversing along its rails or lifting activities.
Further CAD modeling is required.
Figure 12. Steam Turbine Valve Rack Lift with Overhead Crane Shown in Digital Twin
The scan data simply enables the development of those models through importing the scan data directly into a CAD software. For equipment and features around the ethylene train that did not require animation, importing the processed scan data directly into the environment was acceptable. For instance, railing around machinery platform was included in the environment to show spacing constraints. However, the railing could not be hidden or removed within the digital twin since it was not modeled using a CAD software.
Figure 13. Field Work Area within Digital Twin
Tasks executed in a shop environment can also be included within the digital twin. Continuing with the ethylene train example, each of the machines were overhauled using virtual assembly. As a result, each of the centrifugal compressor spare rotors were assembled with seals, bearings, and coupling hubs in a shop environment while the machine bodies underwent work in the field. Critical steps such as seal and bearing installation can be animated within the digital twin with the necessary granularity. Figure 14 shows a compressor rotor being assembled in a shop during the turnaround.
Figure 14. Spare Centrifugal Compressor Thrust Bearing Installation Procedure Explained in Digital Twin
Though animations within an interactive 3D environment are incredibly helpful, there are times when additional context or instructions are necessary to include. Most digital twin platforms include a method for including text instructions at critical tasks. These steps may include warnings, hold points, special tool instructions, or just supplemental information regarding the task. Figure 15 shows an example where additional text is useful in guiding personnel through the task
Figure 15. Centrifugal Compressor Coupling Hub Installation Procedure Explained in Digital Twin
One crucial benefit of a digital twin is the ability to develop mock lifting activities. For the ethylene train, lifting the upper half steam turbine casing and rotor were replicated within the digital twin to evaluate spacing constraints within the lift bay. The actual lift beam and rigging were modeled and included to optimize the plan and train personnel prior the turnaround. Figure 16 shows the spare steam turbine rotor rigged and connected to the overhead crane in the crane bay.
Figure 16. Steam Turbine Rotor Rigging Instructions Explained in Digital Twin
In addition to training new personnel and guiding users through turnaround execution, digital twins are an invaluable tool for performing a “dry run” in preparation for a turnaround. The digital twin for the example ethylene train was used to train engineers, technicians, contractors, management, and operators several weeks prior to the turnaround. The step-by-step process was shown to the group highlighting the sequence of events, special tools, rigging and lifting instructions, and less-known tasks such as virtual assembly. Transferring this knowledge from the planning team to the broader execution team is of utmost importance, and digital twins enable a paradigm shift in knowledge transfer. The integration of both virtual assembly and the digital twin helped the team execute the ethylene train turbomachinery scope in half the duration relative to the previous turnaround a decade earlier.
Throughout the turnaround, personnel leveraged the digital twin on computers and mobile devices. The team checked off tasks, made important notes, and took hundreds of pictures that were all connected to the digital twin. All of this data can be used to make updates to schedules and detailed plans associated with future turnarounds. The digital twin can also be updated to show improvements to sequence of events or to show future work scope changes. Assuming new facilities or new equipment is installed in the unit, the digital twin environment can be updated to include those additions.
CONCLUDING REMARKS
This paper has offered an overview of how technology is transforming the way in which turbomachinery turnarounds are planned and executed. Virtual assembly has enabled a paradigm shift in overhauling complex machines such as steam turbines and centrifugal compressors. Most traditional time-consuming measurements have been eliminated. Iterative tasks such as lifting a rotor in and out of casing to measure and adjust critical clearances is no longer necessary. Critical tasks associated with assembling a rotor, seals, and bearings in a compressor casing were once required to be executed in series, resulting in long turnaround durations that were normalized across all industries. However, virtual assembly enables parallel workflows, such as building the rotor, seals, and bearings in a controlled shop environment with certainty that all components are precisely installed to replicate the required placement once installed into the compressor casing. In addition to reducing turnaround durations, there is a notable risk reduction as a result of minimizing lifting activities. The probability of human error decreases with the reduction in work tasks. Personnel spend less time onsite because of the reduction in duration, and the time spent onsite is safer because of executing much of the critical work in a controlled shop environment and only being exposed to a fraction of the critical lifts relative to historical turnarounds.
However, virtual assembly requires significant planning and technical forethought. Dedicated teams with experienced resources are vital to ensure a successful plan is developed. Maintenance digital twins are an invaluable tool for teams to develop complex visual representations of works tasks at a granular level. Exact replicas of the work environment can be developed ensuring the planning team understands logistical challenges, spacing constraints, and resource loading. The exact sequence of events can be replicated in a virtual environment and optimized based on group feedback from studying the animations in advance of the turnaround. Digital twins enable knowledge transfer from senior engineers and technicians to less experienced personnel. Engineers, technicians, contractors, and operators are collectively trained prior to turnarounds to ensure alignment amongst disciplines and various workflows. Digital twins can be used throughout execution so that personnel can view real-time updates regarding schedule, see important notes, and view pictures taken during disassembly or by the opposite shift. Post-turnaround improvements to the digital twin enable further optimization of future turnarounds by incorporating lessons learned within a powerful, visual tool. Ultimately, advancements in technology are transforming turbomachinery turnarounds and creating immense value for end users.
REFERENCES
1. Simpson, K., Francis, T., Judice, J., “Transforming Maintenance Using Virtual Assembly,” Proceedings of the Turbomachinery & Pump Symposium, 2024.
2. Parker, R. W., Collier, D. H., Rudisel, D. A., Rutan, C. R., and Pyle, A. S., “Planning, Preparation, and Implementation of
Turbomachinery Turnarounds,” Proceedings of the Twenty-Fifth Turbomachinery Symposium, Texas A&M University, 1996.
3. Hexagon Metrology, “AT960 Laser Tracker Technical Data Sheet,” 2023. [Online]. Available: https://hexagon.com