Frequently Asked Questions

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Preventance Primer is recommended if:

You need a quick start on building a PM program, especially for critical equipment. Primer is easy to understand and simple to operate; perfect when you don’t have time for a lengthy learning curve. The Primer strategies and will deliver good reliability but they not tuned to precise reliability targets nor to your specific plant history (e.g. bad actors). They are thus not intended to closely match your business cost objectives.

For non-critical equipment you may find the PM strategies in Primer to be conservative. If you are budget limited and are targeting significant amounts of non-critical equipment you should use Preventance Planned rather than Preventance Primer.

Preventance Planned is recommended if:

You need reliable PM strategies that fit your operating circumstances for critical and non-critical equipment, including options with different risk tolerance. Nevertheless, Planned is suitable when you don’t have time for a lengthy learning curve, as it, too, is simple to operate and requires little training.

Preventance Planned provides a range of strategies and lets you explore the reliability consequences of customizing PM task intervals within and around this range. It is the best tool to safely tune the strategies to required reliability targets or to accommodate your plant history (e.g. bad actors). However, Planned is not intended to model your business costs nor to address specific business objectives such as to minimize direct costs.

Preventance Precision is recommended if:

You need reliable but ‘balanced’ PM strategies that fit your operating circumstances for critical and non-critical equipment. Balanced solutions mean that Precision lets you use your plant-specific cost data to optimize the strategies and makes special efforts to balance the desire for equipment reliability with business priorities, such as maximizing the net plant level benefit for critical assets and minimizing direct costs for non-critical assets.

Precision is the tool specifically equipped to seek solutions that optimize reliability and cost in a way that achieves World Class Maintenance. The diagnostics found in Precision also make it the ideal tool for troubleshooting preventive strategies from a reliability or business perspective. Despite these capabilities it is simple to operate but it does require more data input and more training than Primer or Planned.

In the early 1970s RCM introduced the concept of criticality and a formal analysis for its determination. It applied an FMEA to specify the degraded states of equipment and used the criticality level to gauge the level of mitigation needed for each degraded state. Maintenance technology has remained indebted to RCM for these seminal advancements.

However, as a result of intensive work during the ‘80s implementing RCM in commercial nuclear power plants, the US Electric Power Research Institute (EPRI) sponsored changes to the RCM process to make it faster, less expensive, more consistent, and more dynamic, and within a few years created a database by which practitioners could benefit from world-class equipment expertize:

a. The lengthy RCM criticality analysis was replaced by a criticality checklist that is easily applied at the asset level.

b. RCM used two “bins” of criticality (critical and non-critical) but left the operating context as a continuum of unspecified variables. When two-part binning of duty cycle and the service conditions was introduced, PM strategies could be summarized in PM Templates. Further, the FMEA can then be modified to describe the asset type, instead of an instance of the asset type, as in RCM. The resulting FMEA Template is then applicable and easily updated across all applications of the same asset type, whereas with RCM, a new asset of the same type in a different application needs a complete new analysis.

c. The nuclear industry’s RCM implementation program found that plant personnel usually lack the experience to develop accurate and comprehensive descriptions of the degraded states, as well as failure patterns and time scales for degradation, which limited industry confidence in the resulting RCM strategies. As a result Preventance authors developed the first purpose-built Templates under EPRI sponsorship in 1996 using equipment experts hand-picked by leaders in the power industry. Over the following 8 years the Templates evolved into the EPRI PM Basis Database (PMBD) and APT’s equivalent PRO-M desk-top application (under license to EPRI).

d. At this point using Templates could already be seen to be faster, cheaper, and more dynamic than RCM, with superior internal consistency and much more engineering knowledge at hand. Preventance authors soon added enhancements going further beyond RCM: 1) the effectiveness of PM actions in mitigating degraded states was quantified to improve on RCM’s vague “applicable and effective”, 2) a simple model was added for the decrease in task effectiveness when a task interval was increased in relation to a wearout time, 3) the overall failure rate was estimated depending on PM task intervals and the operating context.

e. Preventance, APT’s web-based successor to PRO-M, has now been benchmarked against independent published data, it accounts explicitly for task repetitions, it includes modeling of the economic impacts and costs, and automatically searches for task combinations that improve the net benefit of a PM strategy, while taking account of increased risk aversion for critical assets. During 2014 the data and technology were formally endorsed by the US Nuclear Regulatory Commission.

f. RCM technology remains exactly where it was in the ‘70s. It can still be a useful tool in special circumstances but its history across many industries of repeated failed sustainability due to high cost and lack of dynamic updating ability have resulted in its not being widely viewed as a general purpose industrial strength technology.

Yes, the data structure is the same across all three product levels but, 1) there will be a need to edit the criticality checklist in Precision if it had not been used in Primer or Planned, and 2) there will be a need to edit the values of cost parameters.

When a company obtains a license to Preventance it is provided with a single Admin account in a single division named “Company”. The company Admin account owner can create additional Admin accounts and User accounts in his own division, in other existing divisions by selecting them, or in new divisions simply by naming them when he creates the accounts. Any Admin account owner can do the same thing, i.e. create Admin and User accounts in any existing division as well as in new divisions of their own invention. Any Admin account can also be a User account and is counted for licensing purposes as a single account. The total number of accounts cannot exceed the contracted number of licenses for the company.

Within a company Preventance permits the creation of any number of company “divisions”, which are arranged in a simple hierarchy. Preventance is agnostic regarding the nature of divisions, some of which may represent organizational levels, geographical boundaries, plant sites, individual plants, or even parts of plants.

Any new Division (i.e. one that has not already been created) is considered to be at a lower level than the division from which it was created. All divisions directly created from the same ‘source’ division are considered to be at the same level in the hierarchy regardless of the Admin account that created them. The hierarchy structure is thus strictly one of division levels, and is entirely independent of User and Admin accounts. But each account ‘takes on’ the level of the division to which it was assigned.

Divisions B1, B2, and B3 are all at the same level, one below Division A. Divisions C1 through C8 are all at the same level, one below Division B.

No user can view analyses or even the list of analyses performed by other users unless his User account is created in a division at the same or higher level than theirs. If that hierarchical requirement is satisfied, the user will be able to view analyses, including complete details of results, created in divisions other than his own. In the figure above, User accounts assigned to Division B2 can thus access results produced in Divisions B1 and B3 as well as those from C1 through C8, but they cannot access results from Division A. Users in any of the C Divisions can see each other’s results but not those of users assigned to Divisions B1, B2, or B3, nor A.

To see results in a different division a user will need to select the other division using the menu item “Sites….. Select Site”. For labelling the menu, “Site” means “Division” as Site is probably more commonly used for equipment and plant location. Having selected the division he wishes to temporarily “work at”, he will see only analyses from that division.


No user can edit the analysis performed by another user in any division, even his own, although he may view it if he has access to it. To make use of another user’s analysis a user must copy it, whereupon the copy is assigned as his own.

The Status of a particular analysis owned by a user can only be changed by him (in Analysis Actions at foot of Component Details Panel). He can select “In Progress”, “Complete”, or “Benchmark”. If he assigns Benchmark, that analysis can thenceforth not be edited by anyone, not even its former owner, and it can only be deleted by an Admin account. The Benchmark status can be applied to a component analysis or a FEG. Benchmarks are thus roughly equivalent to a company Template although they only address a single analysis, i.e. a unique criticality and operating context, rather than the full range of these.

AR means As Required. There can be several reasons why a specific interval is not provided:

a. If the task is recommended to be only done on-condition, e.g. when some other task shows the need for it – see the task details.

b. If the task is typically a hidden failure-finding task the interval will likely depend on the failure rate and the tolerance for unavailability.

c. If the task is typically governed by industry standards such as ASME requirements or by plant license requirements in a regulated industry.

d. Sometimes a Refurbishment or Overhaul interval is given as AR when the consensus is that it would not normally be a scheduled task but special circumstances might on occasion require it. In that case it is useful to know the basis and content of the task and to be able to calculate the reliability benefit of doing it.

e. When the interval is recognized to be highly application-dependent.

NR means not required and NA means not applicable. These have somewhat similar meanings and are only used to fill in the PM Template for certain cases where other criticality or operating context columns in the PM Template do have specific intervals. NA generally indicates that the equipment is not likely or not ever used in that mode.

The expert panels are very knowledgeable about the best task intervals needed to achieve high reliability. Their recommendations do fit general financial constraints of budgets and the operational constraints of operating plants, particularly in the power industry. Despite this, it would be irresponsible to assume that these recommendations can apply unchanged to your particular business priorities, management tolerance for risk, or specific equipment and plant history. Consequently, Preventance contains tools that enable you to customize the strategies in both business and reliability spaces while automatically maintaining an RCM-like vigilance over risk priorities. The diagnostic tools will tell you very precisely the most important characteristics of the customized solutions.

When Precision is searching for a higher benefit strategy it changes task intervals in small increments and in the direction of fastest approach to a maximum net benefit. The scale of net benefit is usually many tens of thousands of dollars. For two reasons the search routine requires the net benefit to change by at least a minimum amount before any task interval gets changed during optimization: 1) it is unwise to chase the last dollar of benefit because there are always uncertainties in the costs and the models, and 2) the acceptability of even incremental change in the resulting reliability and cost benefit must recognize that risk tolerance is much less for critical assets than for non-critical assets. In practice, Preventance adopts different levels of this resistance to move away from the ASL recommendations.

Through this mechanism the Higher Benefit mode is just more cautious than the Maximum Benefit mode. It usually does not result in attaining the absolute maximum benefit and it often brings a different kind of advantage, which is that the higher benefit strategy is more likely to be acceptable without further manual customization because most task intervals will not have changed by as much as when seeking the maximum benefit.

Wearout times are indicated by a time frame in years following the letters “UW” for a universal wearout or just “W” for a conditional wearout. The time frame is the expected earliest time before failures will begin to occur and corresponds to the start of the time to failure distribution. When the time frame shows a range it indicates uncertainty in this earliest time. When there is an uncertainty, Preventance uses the average of the range. A universal wearout process will always be operating whereas a conditional wearout needs some trigger or special condition to initiate it. The triggers are called stressors and the user can turn one or many of them on whenever he sets the Service Conditions to be Severe. Each degraded state (row) in the FMEA will be coded as being a W or UW wearout or a random (R), and will contain any stressors that may apply (i.e. if the user has ‘turned them ‘on’). Preventance uses this information at run time to determine the contribution to the failure rate from that degraded state.

The effect of an active stressor on a universal wearout is to shorten the wearout time by a factor of two, thus UW10 with an active stressor means that failures could start after just 5 years, not 10. A conditional wearout that does not have an active stressor has only a negligible contribution to the failure rate. The effect of an active stressor is to ‘turn it on’ by treating it as a UW with the stated time frame (not with a shortened time frame). Thus a W12 is essentially ignored by Preventance unless it has an active stressor, whereupon it is interpreted as a UW12.

An unstressed Random mechanism also has only a very small contribution to the failure rate, but that is multiplied by a factor of ten when there is an active stressor.

RCM requires that a wearout mechanism for which no mitigating task can be found and no cost-effective design change can be implemented to be recognized as such, with an explicit acceptance of the risk. Preventance adopts similar rules. In both the baseline and custom strategies you can observe the ‘red’ wearout degraded states, which are those that have very poor mitigation or none at all. In addition, Preventance monitors the loss of mitigation, if any, that occurs during optimization and customization. If a degraded state has at least a factor of ten mitigation in the baseline strategy and less than a factor of ten in the custom strategy it gets flagged. The diagnostic information reveals the extent of its contribution and shows the time scale over which it can be expected, on average, to contribute one additional failure. Note that at present the flags and the ‘red’ wearout states do not use the same criteria. Note further that it is not at all uncommon for the baseline strategy to fail to achieve a mitigation of a factor of ten for many degraded states and so these cannot contribute to the flagged states. Over time the criteria for flags and red wearouts will be brought into alignment.

A FEG is special combination of any collection, i.e. group, of analyses the user cares to create. The aim is to enable the formation of an assembly of equipment, which does not already exist in the ASL as a component type, but which can be constructed from component types that do exist. Before being added to a FEG a component type should have its analysis completed because only limited editing is permitted once in the FEG. There are two principle uses. The first is to edit PM Task Intervals for FEG components so they make practical sense for an assembly that will have at least some tasks performed at the same time on at least some of the components (e.g. for a motor, coupling, pump combination). The second is to enable different instances to be created of basically the same “machine” where the different instances are composed of different numbers of the same constituent components (e.g. cranes which may have different numbers of motors, gearboxes, hoists, etc). Despite these principle uses, there are no rules that limit what can be put into a FEG, thus there are no limitations.

A limitation is that the combined failure rate is the sum of the constituent failure rates so from that perspective the FEG is considered to be a series reliability block diagram such that failure of any FEG component represents a failure of the combination.

A PM Group is a group of components that will all have the same, or nearly the same, PM strategy. PM Groups accelerate a PMO project when it is desired that every item of equipment should have its PM strategy developed with all the data fields completed before transmittal to the plant CMMS. A PM Group enables one such equipment item to be analyzed completely, after which all its results can be automatically copied to all members of the group. After copying the results for the “Lead Tag” to all group members, individual members can still have their results modified, e.g. if they require some task(s) to be done at a different interval or have a new task added.

The direct cost of repairs includes repair after failure and repair of degraded conditions discovered during PM task performance. Since essentially all PM tasks except lubrication only discover degraded conditions rather than prevent them, the direct cost of repairs is always accounting for repairing almost the same level of degraded conditions regardless of the degree of PM performed. Preventance does account for various second order effects such as the generally higher level of damage that accompanies in-service failures, but the result is that the cost of repair is nowhere near as dependent on the failure rate as you might expect.

We continuously strive to bring you the latest data and the most accurate results possible even though this requires inevitable changes from time to time. Enhancements to data on key components over the past two years have enabled “full functional failures” to be distinguished for the first time from “all failures” for those components. Even though full functional failures can also be defined in more than one way, they are intuitively more constrained than “all failures”, which can cover a much wider range of events that may often not rise to the level of complete loss of at least one of the major component functions. The improvement in recognition of full functional failures for a subset of ASL components enabled a 2015 comparison with statistically accurate data of the same kind, published as the European Industry Reliability Database, EIReDA. This latest comparison was made even more accurate by selecting data sets which had the least uncertainty in preventive maintenance that had been experienced by the EIReDA equipment. This contrasted with our previous comparisons that had sought to cover as wide a range of equipment types as possible. In Preventance, the calculation engine uses the same model for full functional failures as for all failures, the difference being only the constraints on the failure mechanisms that are included.

Preventance includes degraded states that would be considered as “maintenance issues only” in addition to those that are failures of the main functions of the asset. Their inclusion was required by EPRI when the database was created so that it could document all the maintenance issues and not forget about them. The Asset Strategy Library now includes codes for 3 types of Functional Failure Modes (FFM) for all the equipment types. Users can select certain combinations of functional failures to participate in strategy development, if desired. Users may also edit the FFM codes for all degraded states. Further information that is provided in Preventance at the Help icon, (?), on the Edit FMEA Tab is essential for correct use of the FFM options.

The definitions for the 3 classes of Functional Failure Modes are as follows:

FFM 1: The degradation and its cause would produce an equipment functional failure in a very short time if not immediately addressed (i.e. repaired, fixed, replaced). CREATES A FUNCTIONAL LOSS AND FAILS FAIRLY QUICKLY.

FFM 2: The degradation and its cause would produce an equipment functional failure after a much longer time than that of an FFM 1 if not addressed (i.e. repaired, fixed, replaced). Creates a functional loss but fails more slowly, or there are multiple elements that must fail before the degradation becomes a true problem (e.g. multiple bolts or winding ties). If suitable monitoring or other observational means are available (that are not included in the formal PM strategy) these degraded conditions are consequently less likely (<20% chance) to result in a functional failure than are FFM 1’s.

FFM 3: The degradation results in a long term unacceptable or undesirable operating condition (e.g. a housekeeping issue such as a water or oil leak). Does not fail but is an unacceptable nuisance (i.e. is a maintenance issue only).

Any periodic PM task is intended to be performed in a regular sequence of task events separated in time by the task interval. Occasionally it may become difficult, impossible, or too costly to perform one of the task events, so it’s not done until the next scheduled task event. The task is then said to be deferred for one task interval. In practice the deferral period could be any time period or number of task intervals. Until now no one has been able to accurately assess the effect of deferrals on failure rate and risk. Previous attempts have been limited to doubling the task interval, which is too conservative because in a one-interval deferral only one task event gets omitted rather than half of them. The risk of deferring a PM task is an operational usage and has nothing to do with PM strategy development.

Preventance Task Deferral is an off-line calculator and runs on the Custom Strategy. It requires a current analysis record to have been set up to represent the component in question and its current PM program. Thus it can be done immediately for an existing record, or it will need a new analysis record to be set up. Some users may find it convenient to calculate and print off results for the most likely deferrals that could occur as soon as strategy development is completed for a component, so they are immediately available during plant operations. Because risk is the quantity of most interest, Preventance does not currently estimate the cost implications of task deferral, which are normally quite small. Once you have a record set up that represents the current strategy in the custom column you can go straight to the Deferral Tab.

Deferral results are presented in a new table on the same page and will not change any of the existing results of the analysis record. Deferral risk can be calculated for any number of years or task intervals. Preventance can also defer more than one task at a time for the same component. You can print the deferral result using your browser’s print function.