Reliability and Safety of Technical Systems | |||||||||||||
Reliability and Safety Engineering during System Life Cycle | |||||||||||||
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Main Goals | Basic Tasks | ||||||
Evaluation | |||||||
Optimized Design | |||||||
Manufacturer |
System Reliability and Safety Analyses | ||||||
Risk Analyses | |||||||
Authority |
Accepted Risks | ||||||
Optimization of Design, Operation and Maintenance |
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reliable available safe |
Reliability and Safety Assessment | ||||||
Carrier |
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Minimal Costs | |||||||
Reliability and safety engineering include the following tasks:
Appraising alternative system solutions in the evaluation and concept phase | |
Risk analyses: hazard analysis, risk definition, risk assessment, confirmation of acceptance criteria | |
System analyses and optimization of the system structure (redundancy, safeguards, diagnostics, maintainability), operating sequence (in case of disturbances and emergences), ergonomic assessment/ operation, spare part organization, logistics | |
Specification of requirements to system safety, reliability and availability | |
Verification of the required safety, reliability and availability by probabilistic analyses and/or deterministic methods (conformance with safety standards) | |
Verification of the required safety, reliability and availability by statistical methods using service and/or life tests data | |
Development of economical maintenance methods and construction of the maintenance plan | |
Building a cost model for investment cost, operation and support costs in order to estimate alternative system, operating and maintenance solutions (Life Cycle Costing) | |
Building a safety plan for emergences, event feed backs and measurement planning | |
Building an action plan for disruptions: analysis of disturbance scenarios, establishing operating sequences and recovery procedures. Building check lists and instructions. |
Brief (non-mathematical) Explanation of Terms
Life time, failure safety,
availability... Always clear what it
means?
The term around reliability and safety are often used misunderstandingly.
Here is a short explanation, which do not claim to be precisely. But, hopefully,
is commonly understandable. Anyway, descriptions are conform with common
standards.
RAMS: Reliability, Availability, Maintainability, Safety
RAMS Terms, Typical questionings and commonly used measurements |
Move the mouse pointer over the terms | |||
Risk
Risk
in addition to safety, considers the severity of safety critical failures and weights them according to their acceptance Are consequences for humans and the environment tolerable, accesptable, undisirable, unaccesptable, ... ? Frequency of occurence x hazard severity
Useful Life
Useful Life
is the intended service life of a system or a component, during which the specified reliability, safety and availability are met under the stated maintenance activities How long is the system/ the component (economically) maintainable, are spares obtainable, etc. ?
Service life in years, |
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Safety (S)
Safety (S)
is defined as reliability, but considers safety critical failures How many dangerous/ critical/... failures ?
As for reliability:
Availability (A)
Availability (A)
in addition to reliability, considers the down time and preventive maintenance Will it really work when I need it ? Ratio of available operating time to observed mission time (a probability)
(Unavailability is the complement: |
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Reliability (R)
Reliability (R)
is associated with freedom from failures (no malfunctions or component breakdowns) How many disturbances, interruptions, repairs, ... ?
Number of failures per time unit, e.g. per year (failure rate)
Maintainability (M)
Maintainability (M)
has an important influence on availability and the maintenance cost Items easily replaceable, repairable, testable, etc. ?
Mean time to repair (MTTR),
Maintenance
Maintenance
comprises all actions intended to retain and restore normalcy |
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