D4R Project Management

 Management of a Design for Reliability project should be the same as any engineering project, it should include a target, a scope, time and resources, both human and financials.

 Using agile project management methodologies, as Scrum methodology. is a good recommendation to manage this type of project.

 Scrum allows effective management of complex and high-risk projects, ensuring results; in order to do it, Scrum splits the project into short milestones, or Sprint, to work in parts of the project large enough to be considered a deliverable. 

 A Design for Reliability project could include the following parts:

a.  Definition of the level of reliability required by the customer, to set the reliability program goals. The product user is who should define the level of reliability if the level is too high the cost is also too high and the customer doesn't appreciate it; if the level is too low we will have claims and loss of trust, so we damage our brand. 

We can know our customers' opinions by surveys and by studying claims and warranties.   

b.   Product reliability assessment, in working conditions and for estimated operation time. The easiest way is to perform a qualitative analysis by Failure Modes and Effects Analysis (FMEA), it allows us to define the failure modes, their causes, how to prevent/detect them, and their effects for users, and assess them by a Risk Priority Number (RPN). This methodology allows us to define a ranking of the level of reliability of the product. 

c. Reliability modeling, showing the weakness of product and improvement opportunities. The modeling could be done by Reliability Block Diagram (RBD) and Fault Tree Analysis (FTA), these methodologies provide quantitative results and allow us to identify the weakness of design and try new elements and settings.  

d.    The reliability functions estimation, they allow performing a quantitative reliability analysis. When we have prototypes or real products working we could analyze real failure data and define the reliability function, failure function, probability density function (pdf) and failure rate function; with this function is possible to calculate life data, warranties, etc. 

There are several probability distributions that allow defining these functions, Weibull distribution is the most common, it requires to calculate three parameters: shape parameter, scale parameter, and location parameter, that usually has a value of 0 in this type of analysis.

e.  Performing accelerated life tests, like Highly Accelerated Life Test (HALT) and Highly Accelerated Stress Screening (HASS), to confirm data and study possibilities of improvement. Testing prototypes in real conditions is too slow and expensive, an alternative is to design an accelerate testing, increasing the stresses to induce failure, most common factors are temperature, vibrations, electric parameters, humidity,... then testing the prototype to failure, and use power relations (as Inverse Power Law Relationship), exponential relations (as Arrhenius relationship or Eyring relationship) or mixed relations (as Temperature - Non-Thermal relationship) to estimate the life of the product under working conditions.

This methodology allows to modify the design and test the result in a faster and cheaper way, but require the right failure modes identification process to ensure the results are reliable. 

f.  Performing a reliability growth program, to reach the reliability target based on customer requirements. The Reliability Growth program should include the components discussed inside this post, development of test could be modeling by Duane model, Crow-AMSAA model, Lloyd-Lipow model, Gompertz model or Logistic model.

RCM 3: FMEA vs COFA.

After the taxonomy process, that results in a classification of equipment in systems, subsystems and components, we start the RCM analysis based in SAE JA 1011.

 

The first step is to establish comprehensive alphanumeric equipment identification. Then, we can start to give answers to the first five questions of the SAE JA 1011.

The questions are:

1.  What are the functions and associated desired standards of performance of the asset in its present operating context?

Answers must include all the functions of the asset under the operating context and the level of performance desired.

These functions can be divided into Primary Functions or the reason why the organization acquires the asset, and Secondary Functions or other as environmental integrity, safety/structural integrity, control/containment/comfort, appearance, protective devices and systems, economy/efficiency, and superfluous.

FMEA - 1



2.  In what ways can it fail to fulfill its functions?

These are the failed states associated with each function; they can be Partial or Total Failures.  



FMEA - 2

3.  What causes each functional failure?

These are the failures modes reasonably likely to cause each failure. Lists of failure modes can include failure modes that has happened before, that are currently being prevented, or that are credible in the operating context that can be obtained from technical reports or databases.

Recommend databases for mechanical components are the OREDA – Offshore Reliability Data – Handbook by Det Norske Veritas, and the Handbook of Reliability Prediction Procedures for Mechanical Equipment by the Naval Surface Warfare Center – Carderock Division, this last handbook also includes the effects of failures data.

  Other sources are the results of Root Causes Analysis of unidentified failures.

The failure modes can be classified into one of the following categories: Incorrect Operation, Incorrect Assembly, or External Damage.

To define if a failure mode is Evident or Hidden under normal circumstances is crucial to continue with the analysis and define the best task or action.

FMEA - 3

4.  What happens when each failure occurs?

The answers describe what would happen if no specific tasks are done to anticipate, prevent, or detect the failure. The Failure Effects include all the information needed to support its evaluation, such as evidence that the failure has occurred, if it can kill or injure someone, or to have an adverse effect on the environment, to have an adverse effect on production or operations, physical damages, or what must be done to restore the function of the asset. 

  

FMEA - 4

 

5.  In what way does each failure matter?

These are the failure consequences that must take into account if they are consequences of hidden failure modes; and if they have safety and/or environmental consequences or only have economic consequences.

FMEA - 5

  

At this point, we can consider finishing the full FMEA – Failure Modes and Effects Analysis - giving values to Probability (of the failure mode), Detection (of the failure) and Severity (of the failure consequence) and multiplicity them to calculate the RPN - Risk Priority Number-. This is the methodology most commonly used in RCM analysis. The standard SAE J 1739 gives us a methodology to perform an effective FMEA.

FMEA - 6

Another option is to use the COFA – Consequences of Failures Analysis – the methodology proposed by Neil B. Bloom that defines a Component Classification, based in an RCM COFA Logic Tree, that classify the components in Critical, Potentially Critical, Commitment, Economic, or Run-to-Failure.

The COFA methodology is more straightforward and comprehensive than FMEA to give a final component classification to support the choice of the best maintenance tasks or actions, keeping all the SAE JA 1011 standard requirements.

COFA

1st Post - RCM: Common sense applied to maintenance.

2nd Post - RCM: Taxonomy and core principles.