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TPK 5170 RAMS Assessment and Optimization

...adds new methods and skills to your RAMS toolbox of useful tools, methods, and models.

 

Brief background of course

This course is the specialization course in reliability, availability, maintenance and safety (RAMS) in the last fall semester of the (2 year) international RAMS program and the (5 year) program in Mechanical Engineering (in Norwegian: Produktdesign og Produksjon - PUP).

The course is a continuation of RAMS methods with special emphasise on the application of methods, for example for the optimization of system design, operation, and maintenance. The course is part of the big envelope of courses given from the department of Production and Quality Engineering at NTNU, and it is lectured with personnel that belong to the RAMS group at this department. It is expected that the students already have taken (or have relevant background corresponding to):

  • TPK 4120: Safety and Reliability
  • TPK 4140: Maintenance Management 
  • TPK 5160: Risk Analysis 

This course replaces the earlier arrangement with two specialization modules, one in risk and reliability and one in maintenance optimization (each with 3.75 credit points). The new (merged) course TPK 5170 therefore includes both subject areas: risik and reliability and maintenance optimization, and gives 7.5 credits (i.e., as a regular course normally does at NTNU).

It may be remarked that this course may, from the fall of 2015, change the name to "Asset management methods". A new course in "Reliability of safety-critical systems" may also be introduced. The course content may therefore change as a result of these changes. The changes will be available http://www.ntnu.edu/studies/courses, once implemented. The course responsible person in the fall of 2014 is Professor Mary Ann Lundteigen. I will also give about 50% of the lectures. This this is a specialization course, need the support of some "specialists" on certain topics. Some special topics will thererfore be lectured by Associate Professor Yiliu Liu and our new (at NTNU) Professor Anne Barros. As the course responsible, I will always be present in the lectures (with one or two exceptions) , also those not given by me.

Course objective and motivation

The main objective of this course is to increase the depth of understanding about RAMS methods.

Think about a system. A system will typically constitute many different parts and together they will perform many different functions. The system may be production critical, safety-critical, or even both. Safety systems may be mainly there to protect personnel from injury and death, or to protect the environment from severe damages. Railway signaling systems are one example of the first, and high pressure protection systems onboard an offshore facilitiy may be an example of the latter. Production-critical systems may, if they fail, cost "a whole lot", and have a severe effect on a manufacturer reputation, the quality of products developed, and the costs associated with correcting the system after failure. Critical infrastructures may be consideres as both production and safety-critical. Stable and safe public transportation, clean and stable water supply, power supply, and net supply are important for serving the society and business, and a failure of these could affect safety at a local level as well as at a national level.

Some key questions to ask in relation to such systems are shown in the figure below, and in many cases, they need to be solved using RAMS assessment and optimization methods.

 

This means that methods already introduced in other courses are studied in more detail, with assistance of new application examples and new perspectives. Some new methods are also introduced so that the students, after having taken the course, will have a heavy weighted toolbox of methods to use in their future work tasks.  

Learning outcome

More specifically, the learning outcome should be:

Knowledge:
Basic insight into the theoretical foundation and practical applications of RAMS assessment and optimization. 
Skills: 
Being able to identify and use framework and methods available to solve RAMS assessment and optimization tasks, and to select suitable methods for also more complicated situations. Solve optimization problems in practice. Assess RAMS performance for systems. 
General competence:
Understand RAMS as an important cornerstone of industrial and commercial systems and in the public administration. 

Topics lectured

Topics to be covered are as part of the course are (organized according to whether the application is mainly for safety-critical systems or production-critical systms, or both) presented below. Note that more than one lecture may be used to cover one particular topic. See the lecture plan for more details.

Reliability analysis of safety-critical systems [Six lectures]:

  • Methods for developing reliability requirements for safety systems and barriers, with basis in risk analyses

    Safety integrity level (SIL) is a key reliability performance measure used for safety-critical systems. The SIL requirements are identified in an extension of the risk analysis, using methods often refered to as SIL allocation, SIL targeting and SIL classification. Key methods like Layers of protection analysis (LOPA), risk graph, and minimum SIL are presented and discussed.
  • Extension of methods for quantifying the reliability of safety-critical functions.

    In TPK 4120, some analytical formulas were introduced to calculate the average probability of failure on demand (PFD). It was also shown how the average PFD may be calculated using Markov methods and fault tree analysis. This reliability measure is of high importance in relation to SIL, as a relationship is established between a SIL requirement and the maximum PFD tolerated for a safety function. In this course, we go one step further and:
    • Introduce some other methods for quantifying the average PFD: The analytical formulas presented in a standard called IEC 61508 (in part 6), which builds on slightly different assumptions than the analytical formulas from TPK 4120. In addition, we will introduce the PDS method and Petri Nets.
    • Study reliability of "high demand systems", where another reliability measure, the average system failure rate (called PFH), is recommended rather than the average PFD. One example of a high demand safety system is a machine that carry out safety-critical functions. Also PFH is linked to SIL.
  • Monitoring and maintaining SIL performance in the operational/use phase.

    The reliability of a safety-critical function is influenced over time after the system has been put in operation. Just like if you buy a car: We may think that the car has some kind of inherent reliability performance in light of what it costs, the type of engine, manufacturer reputation, safety systems installed with the car and so on. Nevertheless, once you start to drive it, its performance may change over time depending on your driving habits, how much you drive, where you drive, how often you send it to the garage for maintenance and checks and os on. You may collect some data about the car's performance, such as how often it does not start "on demand", milage, and how often some of the safety-features fail, and based on this (often limited information as you should not have much failures) you may try to estimate the reliability. In fact, you are trying to estimate the reliability as it has been up till a certain point in time. It is the same thing we would like to do with a safety-critical system: With rare data we would like to estimate the reliability with the information we have. If the performance is not sufficient (SIL requirement is not met), we need to do something.

Relevance:

  • Some examples showing the relevance of this topic may be found with consultancy companies, such as with Safetec, Lloyd's Register Consulting, and DNV-GL (link to the GL-part of the services), and Lilleaker Consulting. Manufacturers like ABB, Siemens, AkerSolutions, FMC, Kongsberg Maritime and many more need to design systems in light of SIL requirements, and also demonstrate (sometimes with assistance of the consultancy companies) that the SIL requirements are met. End users, like railway service providers like Jernbaneverket, oil companies like Statoil, Det Norske, GDF-Suez, Shell and Conoco-Phillips among some, and owners of smelting plants, owners of water power stations must demonstrate that the SIL requirements continue to be met throughout the life of the systems.

 

 Maintenance optimization:

 


How to define requirements for safety systems and barriers, and how to assess the reliability of safety instrumented systems with background in IEC 61508 and related standards. This includes SIL allocation, risk acceptance criteria, requirements for design of technical and operational barriers, alternative strategies for treatment of common cause failures, various methods for determining proof test intervals, and trade off between safety and regularity. Within maintenance optimization the following topics are covered: Age, block, and minimal repair policies. Optimisation of intervals and intervention level in condition monitoring models. Optimum grouping of maintenance activities. Spare part optimisation. Reliability Centred maintenance. Data collection and analysis. In relation to technical safety we study how the result from the risk analysis may be utilized to assess the effect of various safety system configurations, and combination of these under various constraints.

Tutorials

Reliability analyses:

Tutorials will focus on the application of lectured methods, and in particular comparing results of using different approaches. Matlab, Maple and Grif (the latter is a rather recent software for reliability assessment in use here at the NTNU) are used in relation to reliability analyses.

 

Maintenance optimization:

 

 

 

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