“Thermal growth” often refers to the change in machinery positions as a machine runs from startup to operating conditions (or vice versa). Machinery positional change can also be caused by dynamic forces, pipe stress and other factors. Compensating for thermal growth is necessary because the machine will be misaligned during operating conditions if it is not. —Daus Studenberg, Applications Engineer – LUDECA, Inc.
Thermal Growth and Machinery Movement Crash Course Video
Machinery movement and thermal growth are two of the main issues that affect operation and life of machinery. Watch our crash course video and see how continuous monitoring of positional change can eliminate checks and calculations and provide an exact solution.
by Ana Maria Delgado, CRL
It is a good idea to complete a few pre-alignment steps prior to conducting any alignment activity. For instance:
- Verify a possible misalignment condition by using a condition monitoring technology such as vibration analysis or thermography when possible. This will help to identify the type of misalignment condition that is present, and any other conditions that could prevent a successful alignment. This may prevent unneeded work activity.
- Conduct a visual inspection to identify foundation deterioration, grout quality issues, broken bolts, cracks in the machine feet or base, etc. These issues should be corrected before any alignment activity is started.
- You may wish take a current power consumption and vibration reading on the equipment prior to any alignment activity and another set of readings after the machine has been properly aligned. This will document reductions in harmful vibration as well as the energy required to operate the equipment resulting from improved alignment.
- Consideration should be given to thermal growth. Accurate thermal growth values should be determined and used during the alignment process. This will help ensure that the equipment is properly aligned during normal operating conditions.
by Trent Phillips
Design, installation and startup are the biggest contributors to a reliable or unreliable plant. It is difficult or impossible for a Maintenance Department to overcome issues inserted during one of these stages. Unfortunately, most often the focus is placed on fixing the equipment after some functional failure has occurred. The focus should be placed on preventing equipment failures in the first place.
Design and installation consideration should be given to minimizing piping strain. Piping strain is affected by temperature, flexibility, mounting arrangement and design. Distortions in machinery from piping strain can lead to increased vibration levels, bearing failures, seal failures, coupling issues and more.
The baseplate should be flat and level. A warped baseplate can lead to soft foot conditions and difficulty in performing proper equipment alignment and reliability issues.
Soft foot conditions distort the frame of the machine and lead to bearing, seal and electrical issues in equipment. Additionally, soft foot conditions can make the normal alignment process much more difficult.
Correct placement and adequate adjustment mechanisms for the equipment are required for proper alignment. The design and installation must allow for any movement required to bring the equipment into proper alignment once it has been placed into position.
Good alignment of the machines also means accounting for any anticipated positional changes in the machines that occur due to thermal growth or operational loading. Compensate for this by aligning equipment to the proper targets in the “cold” condition.
The above items are a few of the things that should be taken into consideration during the design, installation and startup processes. Failure to do so will lead to difficulty in achieving proper equipment alignment. Improper alignment leads to functional failures in equipment and reliability problems. Don’t overlook the reliability improvements that are available to you by doing good equipment shaft alignment.
by Trent Phillips
A lot of maintenance employees believe that small machine trains can be precision aligned more quickly and easily than larger machine trains. This is not always the case! Smaller machine trains are usually less rigid. This can cause the alignment to shift as the anchor bolts are tightened. Almost all small machine trains have some form of soft foot condition that must be corrected because the machine bases are often not flat or of inferior construction. Additionally, thermal growth can have a large impact on smaller machine trains as well.
Don’t be fooled by the size of the equipment you must precision align. It is critical to understand how the size, design, operation and other factors affect the equipment you must align.
by Trent Phillips
Taking the Heat out of Thermal Growth Issues – Part 1 by Daus Studenberg
“Thermal growth” often refers to the change in machinery positions as a machine runs from startup to operating conditions (or vice versa). Machinery positional change can also be caused by dynamic forces, pipe stress and other factors. Compensating for thermal growth is necessary because the machine will be misaligned during operating conditions if it is not.
We offer two methods for the measurement of thermal growth. One is a “snapshot” method and the other is continuous monitoring. Our current line of M3 brackets provide an accurate and easy to use method to take a measurement using the “snapshot” method.
A reading is taken by mounting the sensors and rotating both brackets to create a “virtual” shaft alignment reading across the coupling. A measurement is taken before and after the machine is running. The difference between the two measurements is the change in the alignment.
M3 brackets provide a cost effective method of measuring thermal growth because it can be used with any of our current shaft alignment product line. It should not be confused with the static “hot and cold alignment check” (where shaft alignment equipment is mounted on the shaft and readings are taken conventionally, before and after startup, on a machine that is not running). Assuming that the bracket was never bumped or moved during the measurement, the results are much more accurate than those obtained by the static “hot and cold alignment check”. Below are typical results one could expect to see from startup to running conditions:
Vertical Offset: -24.4 mil
Vertical Angularity: 15.2 mil/10”
Horizontal Offset: -12.3 mil
Horizontal Angularity: 7.5 mil
You will probably notice that a significant amount of angularity exists, which goes against a lot of assumptions in thermal growth calculation methods where it is assumed that the machine will grow an even amount. When taking thermal growth readings using the “snapshot” method, you will want to confirm (establish repeatability) of the measurement. This can be accomplished by taking another reading on cool down. The difference in the cold-to-hot and the hot-to-cold readings should be very similar, but with the opposite sign. This is an essential practice because you are making the assumption that the bracket was never accidently moved or bumped. In Part 2 of this article, we will show how “continuous monitoring” can provide a more complete and accurate picture of what is going on with thermal growth.
by Daus Studenberg CRL
TURBOMACHINERY INTERNATIONAL • May/June 2012
Thermal growth, as used in the field of machinery alignment means machine frame expansion resulting from heat generation. The generation of heat, of course, is caused by operational processes and forces. Materials subjected to temperature changes from heat generation will expand by precise amounts defined by their material properties.
In turbomachinery, thermal growth results from the temperature differences occurring between the at-rest and running conditions. Generally speaking, the greater the temperature difference, the greater the thermal growth. The magnitude of the growth can be calculated from three variables:
?T (temperature difference),
C (coefficient of thermal expansion), and
L (the distance between the shaft centerline and the machine supports).
When machinery begins to generate heat, the temperature difference between the at-rest and running conditions will cause thermal expansion of the machine frame, thereby bringing about movement of the shaft centerlines. This can produce changes in the alignment affecting the offset and/or angularity between the two machines shafts.
If misalignment beyond permissible tolerances occurs in the running condition, it can be observed from both high vibration and excessive power consumption. Operating machinery that is subject to thermal growth without taking into account its effects will result in a loss of efficiency, performance, and reduction in machine or component life.
Relying on the Original Equipment Manufacturers’ data sheets may not be enough as their calculations are performed on a test unit, under specified operating conditions, loads and field conditions which may be significantly different from operating conditions in the field. These differences can drastically affect the amount of thermal growth observed on a unit in service.
Quantifying thermal growth accurately on turbomachinery to determine the amount of positional change between the machines requires expertise and/or the employment of measurement systems.
Download our article “Thermal Growth: How to Identify, Quantify and Deal with its Effects on Turbomachinery”
by Ana Maria Delgado, CRL
Hot alignment checks are often unsuccessful because of delays in installing measuring devices on the equipment which has just been shut down.
Even when good planning and organization allowed you to take readings within minutes of shutdown, these readings only address the so called “Thermal Growth”. Often the effects of thermal growth on alignment had been calculated fairly accurately and the “hot alignment” check confirmed them, but still, excessive vibration persists and continues to be traceable to misalignment.
The problem is that machinery moves during operation for reasons unrelated to thermal effects.
Dynamic rather than thermally induced movements may cause machinery to operate misaligned. Since these dynamic effects disappear before the machinery stops rotating, hot alignment checks cannot measure them.
The non-thermal moves, both vertical and horizontal, are often as large or larger than the thermal moves but much more difficult to calculate. In our experience the dynamic moves are usually ignored.
These movements can be caused by foundation problems, by pipe strains and stresses, loose anchor bolts or changes in the load, etc. Whatever the cause or causes, almost the only way to determine the movements is continuous computerized monitoring of the alignment.
When coordinated with records from the control room it often becomes clear why and how the machinery changed position. Proper “cold” alignment targeting thus becomes feasible and significant operational improvements are usually achieved.
Aside from the well known consequences of less wear on bearings, seals, couplings, etc. it is sometimes possible to increase the load for the equipment and last but not least, power consumption will reduce and result in savings which are a multiple of the cost of the monitoring equipment.
Several monitoring systems have been on the market for many years using dial indicators or proximity probes, etc. and now, fully automatic laser systems like the PERMALIGN and the new Rotalign Ultra LIVE TREND are available with suitably large measuring range.
by Ana Maria Delgado, CRL
The biggest contribution one can make to lower the operating costs of rotating systems is to align them correctly using the real coupling target values. Target values recommended by manufacturers do not always reflect the real machine centerline movements due to thermal growth, pipe strain and dynamic factors. The new ROTALIGN ULTRA Live Trend, a short term continuous monitoring application, helps to exactly determine the relative positional changes between coupled machines during start-up or shut-down. By applying these values, the machines are precisely aligned to reflect normal operating conditions. In addition, Live Trend allows you to establish a trend of the events that influenced such positional changes. With Live Trend you can also monitor pipe growth and any other machine components over time.
- Lower energy costs through reduced power consumption
- Increased mechanical life of bearings, seals, shafts and couplings
- Reduced bearing and coupling temperatures
- Minimized breaking or cracking of shafts
- Reduced vibration
- Reduced machine damage
Reliability starts with precision shaft alignment!
by Ana Maria Delgado, CRL
Ludeca, Inc. presents “Laser Align“, a free reference tool for shaft alignment of rotating equipment. With this app, you can access important reference material and learn about key laser shaft alignment concepts. “Laser Align” features the demanding tolerances that have been the industry norm, pioneered by Ludeca in 1983. These exact same tolerances are used throughout our Laser Shaft Alignment product line.
Laser Align features the following tools with helpful reference guides:
– Short Flex Tolerance Table
– Spacer Shaft Tolerance Table
– Thermal Growth Calculator
This app offers interactive links for additional information on Pruftechnik laser shaft alignment products such as the Rotalign Ultra, Optalign Smart, Shaftalign, Aligneo. It also features links to Pruftechnik’s condition monitoring products such as the Vibxpert, Vibscanner and Vibnode.
Click here to download the FREE Laser Align iPhone/iPad App Today!
by Yolanda Lopez