Reliability Distribution

About Site Filtering in Reliability Distribution Analysis

In Reliability Distribution Analysis, the site is assigned based on the user's selection in the Site control.

Tip: For more information, refer to the Site Filtering section of the documentation.

Data for the analysis can be generated by a query that contains records from multiple sites. Analyses that are created for a single site and that are based on a query containing multi-site data will contain multi-site data. A single-site user with access to the analysis can open the analysis and view all of the multi-site data in an analysis.

A user that has been assigned, at a minimum, to all of the sites that are associated with the records queried by the analysis will have full access to modify the analysis. If this user reloads the analysis, the query will return data based on the sites that were assigned at the time the analysis was created.

A user that has not been assigned to all of the sites that are associated with the records queried by the analysis will be able to view the analysis, but will not be able to reload or edit the data.

Consider an organization that has three sites, Site X, Site Y, and Site Z. The following Reliability Distribution Analysis records exist:

Reliability Distribution Analysis A: Assigned to Site X
Reliability Distribution Analysis B: Assigned to Site Y
Reliability Distribution Analysis C: Assigned to Site Z
Reliability Distribution Analysis D: No site assigned (global record)

Scenario 1: User assigned to only Site X

This user will see Reliability Distribution Analyses A and D.

Scenario 2: User assigned to both Site X and Site Y

This user will see Reliability Distribution Analyses A, B, and D.

Scenario 3: Super User

This user will see Reliability Distribution Analyses A, B, C, and D.

Important: If a Super User modifies the site assignment of a child record from the site assignment that it inherited from a parent record, data integrity will be compromised.

Reliability Distribution Analysis Data Model

The following diagram shows how the families used in Reliability Distribution Analysis are related to one another.

Note: In the diagram, boxes represent entity families and arrows represent relationship families that are configured in the baseline database. You can determine the direction of the each relationship definition from the direction of the arrow head: the box from which the arrow originates is the predecessor, and the box to which the arrow head points is the successor.

In the above image, the Distribution box represents one of four Distribution subfamilies in which records can exist:Normal, Weibull, Exponential, Lognormal, Triangular, Gumbel, or Generalized Extreme Value. When you create a Distribution record using the Reliability Distribution Analysis workflow, the specific family to which that Distribution record will belong will depend on the distribution type that is selected in the Time To Failure Distribution or Time To Repair Distribution section.

As you develop a Reliability Distribution Analysis, you will create records in these families and link them together, either manually or automatically via the options in the GE Digital APM system. Throughout this documentation, we use the term Reliability Distribution Analysis to mean the combination of the Reliability Distribution record and all the records that are linked to it.

About Data Mapped to the Baseline Analysis <Source Type> Window

When you create a Reliability Distribution Analysis from a query or dataset, the Reliability Distribution Builder window will prompt you to map values from columns in the query or dataset to certain values in the Reliability Distribution Analysis. The values that you select to map on the Select Failure Fields and Provide Information For Downtime screens in the Reliability Distribution Builder window will then appear in the associated columns in the Baseline Analysis <Source Type> window. The <Source Type> is Query or Dataset on which your analysis is based.

Note: If the analysis is based on a query or a dataset and contains additional columns that are not mapped to columns in the analysis dataset, those columns will appear in the Baseline Analysis <Source Type> window with the column name in parentheses.

This family is enabled for site filtering, which means that records in this family can be assigned to a specific site, and will then only be accessible to users who are assigned to the same site and have the appropriate license and family privileges. For more information, refer to the Sites section of the documentation.

Details

The following table displays which columns are mapped from fields in the Reliability Distribution Builder window to columns in the Baseline Analysis <Source Type> window:

Reliability Distribution Builder Screen	Reliability Distribution Builder Field	Baseline Analysis <Source Type> Window Column
Provide Information for Downtime	Downtime Field	Downtime
Select Failure Fields	Asset ID	Asset ID
Select Failure Fields	Failure Date	Failure Date
Select Failure Fields	Number of Failures	Number of Failures
Select Failure Fields	Replacement?	Replaced
Select Failure Fields	Installation Date	Installation Date
Select Failure Fields	Number of Subcomponents	Number of Subcomponents

About Failure History By Asset

The Failure History By Asset plot allows you to determine patterns in the failures such as if they are occurring at random, or close together, or more frequently over time. You can view a timeline that shows when each failure occurred for an asset if the data for an analysis contains failure dates for one or more assets. If the data for an analysis contains failure dates for one or more pieces of equipment, you can view a timeline that shows when each failure occurred for each piece of equipment.

Note: Interaction with charts is not available on touch-screen devices.

Details

For each piece of equipment included in your analysis, Failure History By Asset shows when each failure occurred. The pieces of equipment are listed along the y-axis of the timeline. Dates are listed along the x-axis. The timeline illustrates the general distribution of failures over time for the pieces of equipment included in the analysis. It can also be used as a tool for identifying which pieces of equipment do not fit the normal failure distribution pattern. The timeline is not intended to provide specific information about failures and dates.

The range of dates displayed along the x-axis is determined by the failure dates that exist. The timeline will always include all failure dates, including those that occurred outside the Analysis Period.

The start date of the analysis period is always designated on the timeline by a green line. If the start date is the same as the first failure date, the green mark will appear directly on the y-axis. The end date of the analysis period is indicated on the timeline by a green line if it is set to a specific date. The end date is not shown on the timeline if you have selected I want to use today's date as the end date for this analysis.

About Results of a Reliability Distribution Analysis

After you have created a Reliability Distribution Analysis, the following options are available:

Analysis results can include confidence intervals and parameters for the selected Distribution and goodness of fit measures.
Distribution fitting can be done by Least Squares or Maximum Likelihood (MLE).
The four different types of Reliability plots (Probability of Failure, Failure Rate, Probability Density Function, and Cumulative Distribution Function) can be displayed. In addition, you can select between 2 and 10 Distribution Analyses and choose to view and compare all four of the plot types for the selected analyses using the Competing Failure Plots feature.
Reliability Distribution Analyses can support Failures without Replacement, which are needed to calculate reliability for heat exchangers, boiler tubes, piping, and other pieces of equipment where a repair does not necessarily involve changing the whole unit.
The Preventive Maintenance Optimization calculator can utilize the results of the Distribution Analysis and allow you to input the estimated costs of an unplanned repair versus a planned repair. Based on the MTBF and the ratio of unplanned cost to planned cost, the system calculates the optimal time to maintain equipment.
A Failure Probability calculator can utilize the results of a Distribution Analysis; based on MTBF, Beta, and the last Failure Date, the system calculates the probability of equipment failure at the time in the future that you specify. The system also provides the capability to calculate future life based upon a failure probability that the user specifies.
Based on the analysis results, you can generate recommendations for the maintenance and reliability activities that should be executed in the future to maintain best practices in your organization.

Time to Failure

The most important piece of data for distributions is Time to Failure (TTF), which is also sometimes known as Time to Event (TTE) or Time Between Failures (TBF).

Suppose that you have the following timeline, where each number represents the amount of time that passes between failures.

Installation

5

11

23

38

16

22

44

32

Out of Service

You could fit a Weibull Distribution to this data. A Probability Density Function (PDF) is similar to a histogram of the raw TTF data:

The distribution shows:

One failure occurring between time 0 and 10.
Two failures occurring between time 11 and 20.
Three failures occurring between time 21 and 30.
Two failures occurring between time 31 and 40.
One failure occurring between time 41 and 50 (Out of service).

This type of graph counts the number of failures between certain periods. This creates a curve, which you can examine and ask: At 15 time units, how many failures can I expect to have? The answer: Between two and three failures. You are distributing the failures over the life of the equipment so that at any given point in that life, you can calculate the probability that the equipment will fail. This calculation is generated based on the area under the curve, as shown in the previous graphic. In practice, the PDF is adjusted in such a way that the area under the curve is exactly one, and the number on the y-axis represents the number of failures per time unit.

You select your historical data: other pieces of equipment by the same manufacturer, other pieces of equipment in the same location, other pieces of equipment of the same type, etc. For example, suppose that you want to buy a new pump. You could perform a Distribution Analysis on the other pumps of the same model to predict the reliability of the new pump.

Asset Data for a Reliability Distribution Analysis

The Assets section provides following information for each piece of equipment belonging to a Reliability Distribution Analysis:

This family is enabled for site filtering, which means that records in this family can be assigned to a specific site, and will then only be accessible to users who are assigned to the same site and have the appropriate license and family privileges. For more information, refer to the Sites section of the documentation.

Field Caption	Data Type	Description	Behavior and Usage
Asset ID	Character	The ID of the piece of equipment that failed. This is a required field.	You can enter the ID manually.
Datasheet	Character	A link that displays the datasheet associated with the failure event.	This column appears only when a query is the data source for the analysis.
Future Age	Numeric	The future age of the piece of equipment.	The value for this field is calculated by the GE Digital APM system by adding the specified operating time to the current age of the piece of equipment and is read-only.
Future Failure Probability	Numeric	The future probability of equipment failure.	The value for this field is calculated by the GE Digital APM system using the specified operating time and is read-only. You can specify the future time to calculate the future probability of failure.
Installation Date	Date	The date on which the piece of equipment was installed.	You can enter or select a date.
Last Replacement Date	Date	The last date on which the failed piece of equipment was replaced.	The value for this field is calculated by the GE Digital APM system and is read-only. This field does not appear in the grid.
Number of Subcomponents	Numeric	The number of subcomponents contained by the piece of equipment that is selected in the Asset ID column. A piece of equipment can contain multiple subcomponents, such as tubes in a heat exchanger bundle.	This field is displayed in the grid only when the failure type is Failures Without Replacements.
Present Age	Numeric	The current age of the piece of equipment.	The value for this field is calculated by the GE Digital APM system and is read-only.
Present Failure Probability	Numeric	The current probability of failure for each piece of equipment.	The value for this field is calculated by the GE Digital APM system based on the present age of the piece of equipment and is read-only.

Failure Data for a Reliability Distribution Analysis

The Failures section provides following information for each failure belonging to a Reliability Distribution Analysis:

This family is enabled for site filtering, which means that records in this family can be assigned to a specific site, and will then only be accessible to users who are assigned to the same site and have the appropriate license and family privileges. For more information, refer to the Sites section of the documentation.

Field Caption	Data Type	Description	Behavior and Usage
Asset ID	Character	The ID of the piece of equipment that failed. This value is mapped from a query or dataset.	For manually entered data, you can select the first cell in the column and select the Asset ID belonging to the piece of equipment that you added in the Assets section or enter the ID in the cell.
Censored	Logical	A value that indicates whether or not the datapoint is excluded.	Select the check box to censor the data in the selected row.
Datasheet	Character	A link that displays the datasheet associated with the failure event.	This column appears only when a query is the data source for the analysis.
Downtime	Numeric	The amount of corrective maintenance time for the piece of equipment after the failure occurs.	This value is mapped from a query or dataset or manually entered when you create the analysis.
Failure Date	Date	The date on which the failure of the piece of equipment occurred.	This value is mapped from a query or dataset or manually entered when you create the analysis and is required.
Ignore	Logical	Specifies whether the data in the associated row is excluded or included from analysis calculations.	When selected, excludes the data in the associated row from the analysis calculations and plots. When cleared, includes the data in the associated row in the analysis calculations.
Number of Failures	Numeric	The number of failed elements at each failure event.	This column appears only when the failure type is Failures Without Replacements. This value is mapped from a query or dataset or manually entered when you create the analysis.
Remarks	Character	Additional comments about the failure.	You can enter a value in this column manually.
Replaced	Boolean	A value that indicates whether replacements were made following each equipment failure. A replacement causes the entire piece of equipment to be renewed, thus resetting calculation of the time to failure.	This column appears only when the failure type is Failures Without Replacements. This value is mapped from a logical field in a query or dataset or manually entered when you create the analysis.
TTF	Numeric	The Time to Failure is the duration of time from when the piece of equipment is placed into service until it fails.	TTF may be expressed in terms of days, hours, cycles, units processed, etc. TTF values are calculated by the GE Digital APM system based on the failure dates and are shown in gray to indicate that they are read-only.