Skip to main content

Maintenance Strategies Options


A maintenance strategy or option means a scheme for maintenance, i.e. an elaborate and systematic plan of maintenance action. Following are the maintenance strategies that are commonly applied in the plants.

• Breakdown Maintenance or Operate to Failure or Unplanned Maintenance
• Preventive or Scheduled Maintenance
• Predictive or Condition Based Maintenance
• Opportunity Maintenance
• Design out Maintenance

The equipment under breakdown maintenance is allowed to run until it breaks down and then repairing it and putting back to operation. This strategy is suitable for equipments that are not critical and have spare capacity or redundancy available. In preventive or scheduled Maintenance, maintenance actions such as inspection, lubrication, cleaning, adjustment and replacement are undertaken at fixed intervals of numbers of hours or Kilometers.
An effective PM program does help in avoidance of accidents. Condition monitoring (CM) detects and diagnoses faults and it helps in planned maintenance based on equipment condition. This condition based maintenance strategy or predictive maintenance is preferred for critical systems and for such systems breakdown maintenance is to be avoided. A number of CM techniques such as vibration, temperature, oil analysis, etc. have been developed, which guide the users in planned maintenance.
In opportunity maintenance, timing of maintenance is determined by the procedure adopted for some other item in the same unit or plant. In design out maintenance, the aim is to minimize the effect of failures and in fact eliminates the cause of maintenance. Although it is an engineering design problem, yet it is often a responsibility of maintenance department. This is opted for items of high maintenance cost that are due to poor maintenance, poor design or poor design outside design specifications. It may be mentioned that a best maintenance strategy for each item should be selected by considering its maintenance characteristics, cost and safety.

In addition to the above, new strategies concepts such as Proactive Maintenance, Reliability Centred Maintenance (RCM), Total Productive Maintenance (TPM), etc. have recently been evolved to look it from different perspectives and this has helped in developing effective maintenance. In proactive maintenance, the aim is identify what can go wrong, i.e. by monitoring of parameters that can cause failures. In RCM, the type of maintenance is chosen with reliability of the system in consideration, i.e. system functions, failures relating to those functions and effects of the dominant functional system failures. This strategy in the beginning was applied to critical systems such as aircrafts, nuclear and space applications. At present, this is being extended to critical systems in the plant.
TPM, a Japanese concept, involves total participation of all concerned. The aim is to have overall effectiveness of the equipment with participation of all concerned using productive maintenance system.
Labels:

Comments

Post a Comment

Popular posts from this blog

DRY GAS SEALS: How to Implement Proactive Monitoring

BY MICHAEL FORSTHOFFER. In the last 10+ years there has been a significant increase in the technology and instrumentation used on dry gas seal systems to monitor the condition of the seals. Most notable has been the call to monitor secondary seal condition – there have been significant failures of the secondary seal without any issue with the primary seal. The majority of these failures have been due to oil migration across the separation seals. As the oil is not drained out, it accumulates around the secondary seal, fills the grooves, and causes the secondary seal faces to contact. There are various approaches to monitoring secondary seal condition. Probably the most beneficial is utilizing a back pressure control valve in the primary vent (Figure). Figure: Using a back pressure control valve in the primary vent as part of the monitoring of secondary seal condition in a dry gas seal. This sets the primary vent at a pressure below the primary seal gas supply pressure, but high en...
Post a Comment
[Read more...]

How to clean superalloy parts? brazing technique removes oxides in deep, narrow cracks

Investment cast parts used in modern gas turbines are made of expensive superalloys that can withstand extreme thermal, mechanical and chemical loads experienced by hot gas path components. Parts with hundreds of thousands of service hours, however, become severely oxidized. To improve efficiency and reduce the risk of unscheduled outages, these parts must either be periodically refurbished using a brazing repair process or replaced. To facilitate brazing repair, all oxidation, sulfidation and hot corrosion must be removed from surfaces, cooling passages and deep, narrow cracks. Oxide scale typically forms on the mating faces of cracks that occur in hot gas path areas. These cracks become packed full of scale. It is the goal of the service shop to repair these components by filling the cracks with a braze alloy. Unfortunately, braze alloy cannot flow into cracks filled with oxide scale. Figure 1: By varying the pressure between positive, negative, and atmospheric levels, the Dynamic FI...
Post a Comment
[Read more...]

Understanding the Types of Maintenance and Choosing the Right Strategy

This article provides an overview of the nine main types of maintenance, ranging from preventive to corrective maintenance and everything in between. Although specific terminology may vary, it's important to ensure that everyone is talking about the same thing and that the underlying principles are clear. Whether you refer to it as condition-based maintenance or predictive maintenance, what matters most is that we can have a meaningful conversation about when and how to use it. As such, this article also explores the appropriate applications of condition-based maintenance. Many people have questions about the different types of maintenance, so this quick overview provides a helpful starting point: There are nine distinct types of maintenance, which can be classified into two main categories: Preventive Maintenance and Corrective Maintenance.   Preventive Maintenance is performed proactively before any equipment failure occurs. This category encompasses: Time-Based Maintenance (TBM)...
Post a Comment
[Read more...]

Failures in babbit bearings

  There are literally dozens of ways bearings can fail. Some of the more common include: • Babbitt fatigue • Babbitt wiping due to rotor to stator contact • Babbitt flow due to high operating temperatures • Foreign particle damage • Varnish build-up • Electrostatic discharge damage (frosting) • Electromagnetic discharge damage (Spark tracks) • Oil “burn” or additive plating due to high temperatures • Loss of bond between babbitt and base metal • Chemical attack • Pivot wear in tilting pad bearings • Unloaded pad flutter • Cavitation damage This is taken from a paper, Babbitted bearing health assessment" by John Whalen of John Crane, Thomas Hess of Rotating Machinery Group, Jim Allen of Nova Chemicals Corporation and Jack Craighton of Schneider Electric. Babbitt fatigue Babbitt fatigue is caused by dynamic loads on the babbitt surface. Typically in bearings of this type, the dynamic loads are caused by vibration and result in peak film pressure fluct...
Post a Comment
[Read more...]

Grounding brush discharge monitoring

In recognition of the possibility of static charge build up in condensing steam turbines, API 612 (2005) specifies that grounding brushes be installed. The electrical flow to ground through these brushes  be monitored and useful information can be extracted. This article carries excerpts from the paper, “Babbitted bearing health assessment” by John K Whalen of John Crane, Thomas D Hess of Chestnut Run, Jim Allen of Nova Chemicals and Jack Craighton of Schneider Electric. Grounding brushes take current from the rotor to ground so that a charge does not build up on the rotor to the point where it discharges to ground though the best path possible – which is usually the closest point between the rotor and stator which is usually (hopefully) the point of minimum film thickness in a bearing. Typically this point of minimum film thickness is found in the active thrust bearing (as will be shown later). Shaft grounding brushes serve two purposes. The brushes are able to transmit modest amo...
Post a Comment
[Read more...]