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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Texas A&M Repository Proceedings of the Forty First Turbomachinery Symposium September 24 – 27, 2012, Houston, Texas BABBITTED BEARING HEALTH ASSESSMENT John K. Whalen, P.E. Jim Allen Technical Director Senior Rotating Equipment Specialist John Crane Bearings Engineering Technologist Houston, TX 77075 Nova Chemicals Corporation Joffre, Alberta, Canada Thomas D. Hess, Jr., P.E. DuPont Engineering Research & Technology Jack Craighton, CLS Rotating Machinery Group DuPont Engineering Chestnut Run Chestnut Run Plaza Wilmington, DE 19805 Wilmington, DE 19805 John K. Whalen is the Technical Director Refinery, ARCO Chemical in Newtown Square, PA, and for John Crane Bearings. John is a member Bently Nevada as a field vibration analyst. of STLE, ASME, and the Vibration Mr. Hess has a BS in Mechanical Engineering from Institute and is a past member of the Villanova University. He is also a member of ASME, the Turbomachinery Symposium Advisory Vibration Institute, and is a Registered Professional Engineer in Committee; John is a registered the Commonwealth of Pennsylvania. Professional Engineer in the State of Texas. John received his BSME from the John Craighton works in the Rotating Rochester Institute of Technology in 1981. Machinery Group for DuPont located in He spent 7 years with Dresser Rand in Wellsville, NY where he Wilmington, Delaware. worked in Large Turbine Engineering and Rotordynamics. John He is a corporate lubrication joined Centritech Corp. in 1988 and helped form TCE in 1991. consultant responsible for plant level At John Crane Bearings John has Engineering responsibility support and standards development for for all three John Crane Bearing companies (John Crane DuPont. Bearing Technology in Germany, Orion in Wisconsin and TCE Prior to joining DuPont, Mr. Craighton in Houston). The product range includes babbitted bearings and worked for Invensys Operations seals, labyrinth seals, and related products and services. Management and Valero Energy Corporation as a Lubrication Specialist. James “Jim” Allen is a Senior Rotating John is a Certified Lubrication Specialist through the Equipment Specialist in the Reliability Society of Tribologists and Lubrication Engineers. Team for Nova Chemicals, in Red Deer, Alberta. ABSTRACT Jim is responsible for the reliable operation of the Olefins Plants Equipment Within most plants there is often a desire to extend the by supporting operations / Maintenance / time between outages. Several factors determine this but one to Engineering. Prior to joining Nova consider is the bearings ability to run for the extended time. Chemicals Jim worked for Dow Chemicals This Tutorial will address common bearing failure in Fort Saskatchewan, Alberta and Sherritt Gordon Mines, mechanisms, tools available to diagnose these problems and Lynn Lake Manitoba. ways to use that information to make decisions on continued Jim is as certified Industrial Mechanic and Engineering operation. Evaluation consists of analysis of Condition Technologist. He is also member of the CMVA, STLE and has Monitoring information coupled with rotor dynamic analysis been an active member of the world of rotating equipment for and computerized bearing modeling. over 40 years. A case study will be presented that details the evaluation of a distressed bearing. Analysis allowed the user to determine Thomas Hess works in the Rotating they could slightly reduce running speed (to limit vibration to a Machinery Group for DuPont located in certain level) and continue to run to the scheduled outage date. Wilmington, Delaware. He is responsible There will then be a discussion on bearing robustness and for plant and capital project support and ways to design bearings for long life. A case study will be standards development for DuPont. presented where an Ethylene plant desired to extend the time Prior to joining DuPont, Mr. Hess between outages but the existing bearings prohibited that. The worked for Valero at the Delaware City determination was made that upgrading the bearings to a more Copyright © 2012 by Turbomachinery Laboratory, Texas A&M University robust design would allow the extended time between outages. in - or motions of - liquids.” So we have a fluid in motion (oil) that generates forces to separate the stationary (bearing) from INTRODUCTION the rotating (rotor). This may also be referred to as Fluid Film Lubrication since in operation a film of oil separates the Most process plants and power generation facilities are bearing from the rotor. required to maximize the use of their assets by running for The study of this phenomena falls under the field of longer periods of time (longer time between outages) and Tribology (Dowson, 1979) – a word that was coined in 1966: reducing the length of the outage when they are down. Of “…the science and technology of interacting surfaces in course equally important are the need to not come down relative motion and the practices related thereto.” Also often unexpectedly (a forced outage) and the requirement to run referred to as the study of friction, wear and lubrication. efficiently to maximize rates. The basic requirement for successful operation of Many companies have also been implementing hydrodynamic bearings is the formation of the “wedge.” debottlenecking projects throughout their facility and sometimes these result in increased demand from other The Hydrodynamic Wedge equipment in the facility. This increased demand could result in a loss of reliability of that equipment which is being pushed Figure 1 is a sketch of a journal in a bearing (with greatly harder to make rates. exaggerated clearances). This figure also contains some terms Plant owners and operators realize it is important to that will be used throughout this presentation. understand which equipment could limit the time between outages and what component of that equipment is most vulnerable. It is understood that there is a tremendous amount of fixed and rotating equipment; any one of which could be the limiting factor when evaluating the length of time required between outages. It is also recognized that with rotating equipment there are several factors which can influence this scheduling. However this tutorial is only going to discuss oil lubricated babbitted bearings (journal and thrust) as found in existing rotating equipment. To be clear we will be discussing bearings as found in critical un-spared equipment. Machines that should be fully instrumented as per API 670 (2010) as a minimum, and with condition monitoring procedures and processes in place. It is beyond the scope of this presentation to get deeply into condition monitoring practices – it will just be assumed that data is available for analysis. Several failure mechanisms will be introduced discussing Figure 1 Hydrodynamic film generation evaluation of the damage mechanism, tools that may help diagnose the problem while running and methods to avoid the particular failure mode. The intent is that understanding There is a journal rotating (CCW) inside a journal bearing common failure modes can lead to design and operation to and the rotation of this journal drags oil into a converging avoid them; thus pushing the limits of operation. space. Since oil is incompressible, all of the oil cannot be Coupled with this is the evaluation of running equipment pulled though this space so a pressure is generated that forces and the need to determine; if the machine can run to the next the oil out the axial ends of the bearing. This pressure is scheduled outage; if the machine rates (and speed) need to be depicted by the pressure profiles as shown. reduced to ensure successful operation to the outage; if an For the sleeve bearing being considered we see that the outage needs to be taken before the scheduled outage; or if the rotor is displaced down and to the right – since the pressure machine needs to be shut down immediately to avoid further field starts on the left side of the journal. A line drawn between damage. the journal center and the bearing center is called the “line of centers” and the angle between this line and the applied load is HYDRODYNAMIC BEARING OPERATION called the “attitude angle.” The amount the journal is displaced from the center of the In order to be able to diagnose bearing problems it is bearing is referred to as the eccentricity and the term important to have a basic understanding of bearing design and “eccentricity ratio” is the ratio of this eccentricity to the operation. The bearings covered in this presentation include bearing radial clearance. As such an eccentricity ratio of 1.0 babbitted journal and thrust bearings as found in typical special implies the eccentricity equals the clearance and the journal is purpose API turbomachinery. For simplicity, and in order to touching the bearing surface. Likewise an eccentricity ratio of cover the intended machine population effectively, we will not zero indicates the journal is centered in the bearing. be discussing bearings lined with materials other than babbitt, The “minimum oil film thickness” lies on the line of anti friction bearings, magnetic bearings, foil bearings, etc. centers and can be defined by the eccentricity ratio and bearing The definition of hydrodynamic is: “…pertaining to forces radial clearance. Figure 2 is a drawing of the clearance space Copyright © 2012 by Turbomachinery Laboratory, Texas A&M University unwrapped – starting at the point of maximum oil film increases the friction gradually increases. This increase in thickness (opposite the minimum) and continuing 360 degrees coefficient of friction is due to the fact that as the surfaces though the minimum and back to the maximum. Here the separate, the film becomes thicker and the shearing of the converging and diverging wedges can be more clearly seen. thicker film increases the coefficient of friction. Thrust Bearings Thrust bearings absorb the axial loads present in turbomachinery. As journal bearings have to support the rotor, thrust bearings must support this axial load.