The power generation industry has historically had some of the more challenging application requirements in both size and complexity of components. In the hydro or ” water power” industries the sheer magnitude of the equipment has presented engineers with some challenging tasks in dealing with the extreme forces that gravity produces on large scale objects. Material distortion, fatigue, and sag now become as much a factor in the design as does the many tons of force that the water itself imposes on the equipment.
The steam and gas powered turbines are very high speed units, averaging speeds of 3600 to 12,000 rpm and higher. These units are not usually much smaller than their water powered counterparts, and at the speed they rotate the outer edge of the blades can exceed 700 miles per hour. In addition to the dynamic problems of the large assemblies, the speed of operation now introduces a plethora of new problems.
Having many tons of steel, that resemble a giant multi-vane blender, moving at those velocities is not a comforting thought, but even more distressing than the idea of what’s going on inside the turbine, is the dollar figure that arises from downtime or even worse a catastrophic failure that can destroy the machine.
Great care is taken to design and maintain power generation equipment. And in the past, with the tools available at the time, the amount of time it took to properly set up or repair the equipment was horrific Yet without taking the time to do the job right the consequences are even worse.
The amount of information that can be obtained from using the Laser Tracker is tremendous. Not only is there more accurate and repeatable data, but the speed that the data is collected and analyzed is much faster. With the standard 2-D measurement tools that were previously available, there was always a good deal of room for operator error, or at least operator mis-interpretation. This was especially true for the optical measuring devices (i.e. transits, total stations, etc.), as well as the “wire line” or “tight wire” methods. These methods were also limited in their scope of data collection. They were generally used for a single type of measurement, and the data then had to be manually coordinated with data from other tools to complete a better picture of what was going on. Here again there is increased odds of interpretive errors in assembling data from multiple tools and multiple technicians.
The Laser Tracker is a true source of native 3-D data collection. This allows for one tool and one technician to do the job of many, and thereby reduce to overall cost and time requirements of a project, while increasing accuracy.
The data is interpreted by time proven mathematical algorithms and organized into a CAD integrated data base. This allow for high power analysis and clarity in the reporting of the data. Having onboard CAD capability also allows for seamless integration with the repair and remanufacturing vendors that will need accurate and concise information to efficiently complete their portion of the project.
Having clear and accurate data that encompasses all of the major machined areas of the unit allows for trending of distortions and analysis of factors that are causing unexpected changes in the shape and/or alignment of the unit, such as soft foot or foundation settling, pipe and condenser strain, or even weak areas of the forgings, resulting in significant localized distortions that can severely damage the unit and effect performance and efficiency.
Requirements and Techniques
The requirements for power related equipment are greatly dependant on the desired accuracy and depth of the results. If the Tracker is used as a simple replacement for the older technology tools, then the standard requirements for tracker operation will suffice.
There is so much more that the Tracker can do, than simply replace older tools, that I could literally write a book on the subject. So for now let’s simply concentrate on the more prevalent operations that have been used.
Some of the more straight forward applications for power generation include:
The most common operation where the Tracker has proven its capability is thealigning of the internal components of split case turbines and pumps. These include blade ring assemblies, seal housings, inner shells, diaphragms, etc. The alignment accuracy of these components has usually been based on whether or not the rotating assembly comes into contact (“rubs”) with the stationary components. This is the worst case scenario, and is generally not discovered until it’s too late. Using failure, in my opinion, is not a desirable way to measure success, and with the old ways of doing the work, it was unfortunately often the only way to gauge it.
The first requirement for accurate alignment of internals is knowing the required nominal positions of the components, and then the condition of the case that will hold them. Distortion of the case is generally the greatest obstacle to overcome. Relevant data to achieve successful alignment when the unit is assembled requires some additional steps during disassembly. These include at least one of the following:
Optimally, once the insulation is removed, and before the case bolts are loosened, we would attach temporary targets to the lower half of the case near the splitline. These would be recorded in the data base for comparison after the lid has been removed. This will provide an accurate way to measure the change in the lower half of the case, and provide positive data to use for manipulating the internal readings and adjustments that can only be done with the lid off. Using this method will also allow verification that the case returns to its previous position when assembled, by shooting the targets again after assembly.
Some unit are large enough that a person can enter the shell from either end once the rotating element has been removed In these cases the option now exists to re-torque the lid onto the case, and measure the internal alignments with the shell torqued. This eliminates the manipulation that must be done if the alignments are done with the lid off. If the unit will not allow for entry of the technician with “tops on”, then the lid would be removed, and the features measured. Strategically placed targets can then temporarily attached near the smaller bore diameters, where they can be seen with the lid back in place. The points are recorded and the lid replaced and tourqued. The points are shot again and the changes analyzed to verify the change in position when the case is assembled. This allows for positive compensations to be made to the “tops off ” alignments, to be sure that the desired positioning of components is correct after assembly.
If neither of the above options are possible, there is a less accurate, yet widely practiced method. After the rotating element has been removed and both halves of the splitline have been cleaned, set the lid back on the case and take gap readings between the halves with feeler gauges. Take readings, at least, at every bolt location, if not more. This will provide the data needed toestimate what changes should occur when the case is assembled. Again, this is purely based on experienced assumption, as there is no actual data taken on the unit from “tops on” to “tops off” condition.
If option 1 or 3 is used, meaning alignments will be done with the lid off, then one other critical piece of information is needed. With the lid setting on the case, as many bores on both ends of the case as can be reached, should be measured for roundness and size, or at a minimum the bearing bores on both ends of the case. This will allow the data to be compensated for elevational errors that will occur from measuring only the bottom half of an out of round bore (click here for diagram). The more the out of round the bore is, the greater the error in elevation of the measurements. If the internal bores that will be aligned are out of round, then the diameter must be known to compensate.
Finally, the air within the measurement envelope needs to remain as temperature consistent as possible. Mainly that there are not localized areas or pockets of air with significant temperature gradients within the area to be measured. If necessary, the air may be mixed continuously with fans to stabilize it. The operating air temperature range of the Tracker is 50 to 110 degrees Fahrenheit.
The results of using the Laser Tracker in the power industry, as reported by our customers, are:
Faster more accurate alignments of components, which saves money by lowering downtime as well as the overall cost of the inspection and alignment procedures.
Lowered vibration due to better internal alignments, that also result in more uniform heat and flow characteristics. This in turn also prolongs the units lifespan and increases efficiency and output.
Clear and concise data reporting in ASCII, spreadsheet, CAD, and JPG/GIF file formats (click for sample image). This allows for universal data sharing and further analysis of the data by the customer or third party sources. No longer must you take someone else’s word for what the data means. You get finished reports along with the raw data, to analyze or verify any way you wish.
Our customers have been both pleased and impressed by the unprecedented level of service and quality that we can provide using the Laser Tracker, we are pleased at the response and are proud to provide this level of service and satisfaction.