Accendo Reliability

Your Reliability Engineering Professional Development Site

  • Home
  • About
    • Contributors
    • About Us
    • Colophon
    • Survey
  • Reliability.fm
  • Articles
    • CRE Preparation Notes
    • NoMTBF
    • on Leadership & Career
      • Advanced Engineering Culture
      • ASQR&R
      • Engineering Leadership
      • Managing in the 2000s
      • Product Development and Process Improvement
    • on Maintenance Reliability
      • Aasan Asset Management
      • AI & Predictive Maintenance
      • Asset Management in the Mining Industry
      • CMMS and Maintenance Management
      • CMMS and Reliability
      • Conscious Asset
      • EAM & CMMS
      • Everyday RCM
      • History of Maintenance Management
      • Life Cycle Asset Management
      • Maintenance and Reliability
      • Maintenance Management
      • Plant Maintenance
      • Process Plant Reliability Engineering
      • RCM Blitz®
      • ReliabilityXperience
      • Rob’s Reliability Project
      • The Intelligent Transformer Blog
      • The People Side of Maintenance
      • The Reliability Mindset
    • on Product Reliability
      • Accelerated Reliability
      • Achieving the Benefits of Reliability
      • Apex Ridge
      • Field Reliability Data Analysis
      • Metals Engineering and Product Reliability
      • Musings on Reliability and Maintenance Topics
      • Product Validation
      • Reliability by Design
      • Reliability Competence
      • Reliability Engineering Insights
      • Reliability in Emerging Technology
      • Reliability Knowledge
    • on Risk & Safety
      • CERM® Risk Insights
      • Equipment Risk and Reliability in Downhole Applications
      • Operational Risk Process Safety
    • on Systems Thinking
      • Communicating with FINESSE
      • The RCA
    • on Tools & Techniques
      • Big Data & Analytics
      • Experimental Design for NPD
      • Innovative Thinking in Reliability and Durability
      • Inside and Beyond HALT
      • Inside FMEA
      • Institute of Quality & Reliability
      • Integral Concepts
      • Learning from Failures
      • Progress in Field Reliability?
      • R for Engineering
      • Reliability Engineering Using Python
      • Reliability Reflections
      • Statistical Methods for Failure-Time Data
      • Testing 1 2 3
      • The Manufacturing Academy
  • eBooks
  • Resources
    • Accendo Authors
    • FMEA Resources
    • Glossary
    • Feed Forward Publications
    • Openings
    • Books
    • Webinar Sources
    • Podcasts
  • Courses
    • Your Courses
    • Live Courses
      • Introduction to Reliability Engineering & Accelerated Testings Course Landing Page
      • Advanced Accelerated Testing Course Landing Page
    • Integral Concepts Courses
      • Reliability Analysis Methods Course Landing Page
      • Applied Reliability Analysis Course Landing Page
      • Statistics, Hypothesis Testing, & Regression Modeling Course Landing Page
      • Measurement System Assessment Course Landing Page
      • SPC & Process Capability Course Landing Page
      • Design of Experiments Course Landing Page
    • The Manufacturing Academy Courses
      • An Introduction to Reliability Engineering
      • Reliability Engineering Statistics
      • An Introduction to Quality Engineering
      • Quality Engineering Statistics
      • FMEA in Practice
      • Process Capability Analysis course
      • Root Cause Analysis and the 8D Corrective Action Process course
      • Return on Investment online course
    • Industrial Metallurgist Courses
    • FMEA courses Powered by The Luminous Group
    • Foundations of RCM online course
    • Reliability Engineering for Heavy Industry
    • How to be an Online Student
    • Quondam Courses
  • Calendar
    • Call for Papers Listing
    • Upcoming Webinars
    • Webinar Calendar
  • Login
    • Member Home
  • Barringer Process Reliability Introduction Course Landing Page
  • Upcoming Live Events
You are here: Home / Articles / Reliability Block Diagram Fundamentals

by Debasmita Mukherjee 1 Comment

Reliability Block Diagram Fundamentals

Reliability Block Diagram Fundamentals

Basic Definitions

  • Reliability: Ability to provide continuous and stable system/component function under defined operating conditions without failure(s).
  • Mean Time Between Failures (MTBF): Average expected time interval between failures. Often a measure of reliability.
    • Failure Rate is the expected no. of failures over a period of time. MTBF is the inverse of failure rate.
  • Availability: Percentage of time a system or component can perform its intended function without failure.   
    • Key aspects involve individual component reliability, system architecture, redundancy, and implementation of control strategies to ensure uninterrupted service. 
    • Availability = Uptime/(Total Operation Time) = MTBF/(MTBF+MTTR), MTTR is a measure of time to repair the system/component
    • For example, 99.999% (5-9’s of availability) -> 5 min downtime in one year
  • Reliability Block Diagram: Reliability Block Diagram (RBD) is a graphical representation used to model reliability in complex systems. Illustrates interconnections between various components or subsystems within a system.

Fundamentals of Reliability Block Diagram Model

  • In an RBD, different blocks represent individual components or subsystems of the system.
  • These blocks are connected by lines representing the flow of reliability from one component to another.
  • Used to analyze and optimize system reliability by identifying critical components, assess the impact of redundancy and evaluate overall system reliability under different failure scenarios.

Reliability of Complex Systems

For systems without redundancy (margin), the reliability of a system is equal to the product of the individual component’s reliability.

  • To achieve system reliability (NO system failure), there must be NO failure of Components 1 AND 2 AND 3, AND 4 AND …
  • System Reliability, Rs = R1 x R2 x R3 x R4 x …
  • If all components have the same reliability the system reliability simplifies to Rs = RcN    where:
    • Rs = System Reliability, 
    • Rc = Component Reliability and 
    • N = Number of Components

Series and Parallel RBD

Series RBD 

  • Any one component failure leads to system failure
  • Rs = (0.95) (0.95) (0.95) = 0.857 = 85.7%

Parallel RBD

  • System continues to operate if any component or subsystem is operational 
  • 3 parallel subsystems with reliability levels of 90%
  • Rs = 1 – (1-0.90) (1-0.90) (1-0.90)

            = 1 – (0.1) (0.1) (0.1) = 0.999  (3-9’s)

  • k out of N is similar to parallel design where system some built in redundancy to tolerate system failure  

Reliability Metrics to monitor from RBD Models

  • System reliability, availability, mean time between failures and failure rate are all critical metrics we can monitor from RBD models.

Source: Reliawiki

Filed Under: Articles, Field Reliability Data Analysis, on Product Reliability

About Debasmita Mukherjee

Debasmita has used statistical tools and techniques to analyze field data and explore and identify issues, as well as drive root cause investigation. Using automation, she led reliability data analysis at scale to graph performance trends over time.

« Lifetime Reliability Solutions Change To Win Workbook
Test Design for Component Life »

Comments

  1. hayet says

    December 6, 2024 at 6:16 AM

    thanks for sharing this article , really looking forward to read more.

    Reply

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

The Field Reliability Data Analysis logo Photo of Debasmita MukherjeeArticles by Debasmita Mukherjee

in the Field Reliability Data Analysis article series

Recent Posts

  • Leadership Values in Maintenance and Operations
  • Today’s Gremlin – It’ll never work here
  • How a Mission Statement Drives Behavioral Change in Organizations
  • Gremlins today
  • The Power of Vision in Leadership and Organizational Success

Join Accendo

Receive information and updates about articles and many other resources offered by Accendo Reliability by becoming a member.

It’s free and only takes a minute.

Join Today

© 2025 FMS Reliability · Privacy Policy · Terms of Service · Cookies Policy