1st hour:

• Introduction to the course
• Organization of student groups
  (3 persons per group) 

2nd-3rd hours

• Introduction to two case studies
• Group work and summary in
  plenum

Inform the students about the course objectives, intended learning outcomes, and practicalities.

• Give a more thorough introduction to two systems where the lectured models and methods
  may be applicable.
• Explain and discuss the technologies involved, with focus on attributes like
  reliability, availability, maintenance, and safety  

• Student seminar
  this day 

Safety-critical systems:
Key concepts and
requirements

(Textbook: chapter 2) 

IEC 61508 is a key standard on design of safety-critical systems, when the technology used include electrical,
electronic, and programmable electronic systems. Many authority regulations Petroleum, railway, nuclear,
automotive, etc) refer to this standard, or standards that are under the "umbrella" of this standard.
The standard introduces several key concepts including equipment under control, safety integrity level (SIL),
safety lifecycle, functional safety, risk reduction factor, and many more.  Safety design principles, such as
fail-safe design and architectural constraints, are also discussed.

• Selected
  problems 

• Selected
  problems 

Safety-critical systems:
Quantification of reliability
for systems operating
on demand.

(Textbook chapter 8)

Students that take this course are familiar with simplified formulas for calculating the average probability of failure on demand (PFD).
The deriving of these formulas is not repeated here, but extensions are discussed, including:

• IEC 61508-6 formulas
• PDS method (selected topics, with focus on the inclusion of C_MooN)
• Fault tree analysis (compensating for the Schwartz' inequality)

Mary Ann

• Selected
  problems

• Selected
  problems 

Maintenance optimization:
The intervals of maintenance for safety-critical systems are normally determined from the reliability analyses.
For other systems, we may use decide upon intervals of testing using different maintenance strategies
established by the RCM decision logic. These models include parameters like costs, failure rates, and aging.
The models come of with the answer to the following two questions: When should we do maintenance and 
what tasks and equipment should be included. The application of these methods are many. Two examples are
maintenance planning of railway tracks and another is planning of intervention (for maintenance purposes) of
subsea equipment. Sub-topics also covered under the same "umbrella" are:

• Modeling of effective failure rate: Maintenance interval and and intervention level (extensiveness of
  maintenance) is obviously influencing the failure rate of the components. This topic concerns the modeling of the
  relationship between these two parameters and what we can refer to as the effective (or resulting) failure rate.
• Weibull renewal: **Say something here** 
• PF models and state based models: **Say something here** 

Yiliu

(Mary Ann
at the ESREL
conference) 

18.&19.11

Reliability assessment of safety-critical systems       

• Book: Reliability of Safety-Critical Systems: Theory and Applications
• Slides

Development of reliability requirements

SIL allocation

LOPA

Risk graph

Minimum SIL

 PDS method

PetriNet

Architectural constraints: According to standards like IEC 61508, it is not sufficient to demonstrate that a SIL requirement has been met by showing that the average PFD or PFH is sufficiently low and within the specified range of the SIL  requirement. A SIL requirement also poses some restrictions on how a safety-critical function can be designed, in terms of architecture. These requirements are sometimes referred to as architectural constraints.

Partial testing: For some type of components, like valves, it has been more common to also do partial stroke testing in addition to full functional testing. The reason for introdocing this testing strategy may be to improve safety, or to maintain safety while extending the intervall of full function testing. Analytical models have been suggested for this purpose, and we will review these.

Imperfect testing: Many of the methods used to calculate the average PFD assumes that the functional tests are perfect, meaning that all dangerous undetected (DU) falures are revealed by the test. This is not always the case, and the effect of not taking this "imperfectness" into account will be that the average PFD is underestimated. The way this situation is treated overlaps to some extent with how partial testing is modeled.

SIL follow-up in operation: It is important to maintain the reliability performance throughout the whole operational life of a safety-critical system. This may explained by using a car as an example. You may buy a car with a certain designed-in performance, including reliability, based on the engine type, safety features, type of chassis, and so on. Still, the experienced performance of the same type of car may be different for different drivers. If we exclude fabrication errors, the performance of the car is influenced by the driver's driving habits, amount of driving, environment (icy, cold, hot,..), age and so on.

Architectural constraints

Partial stroke testing

Imperfect testing

SIL follow-up

Maintenance optimization and management (1)

• Slides
• Maintenance optimization lecture notes

Age, block and minimal repair strategies.

(2 lectures - Jørn V, Anne)

The intervals of maintenance for safety-critical systems are normally determined from the reliability analyses. For other systems, we may use decide upon intervals of testing using different maintenance strategies established by the RCM decision logic. These models include parameters like costs, failure rates, and aging. The models come of with the answer to the following two questions: When should we do maintenance and what tasks and equipment should be included. The application of these methods are many. Two examples are maintenance planning of railway tracks and another is planning of intervention (for maintenance purposes) of subsea equipment. Sub-topics also covered under the same "umbrella" are:

• Modeling of effective failure rate: Maintenance interval and and intervention level (extensiveness of maintenance) is obviously influencing the failure rate of the components. This topic concerns the modeling of the relationship between these two parameters and what we can refer to as the effective (or resulting) failure rate.
• Weibull renewal: **Say something here** 
• PF models and state based models: **Say something here** 

Spare part optimization:

(1 lecture - Yiliu)