Reliability Growth Testing

Understanding Reliability Growth Testing: A Foundation for Product Success

In the competitive landscape of modern manufacturing and product development, reliability isn't merely a desirable attribute—it's an absolute necessity. For companies across Atlantic Canada's growing technology and manufacturing sectors, understanding and implementing reliability growth testing (RGT) can mean the difference between market success and costly product failures. This comprehensive guide explores the principles, methodologies, and practical applications of reliability growth testing, providing engineering teams with the knowledge needed to develop robust, dependable products.

Reliability growth testing represents a systematic approach to identifying, analysing, and correcting design weaknesses during the development phase. Unlike traditional testing methods that simply pass or fail a product, RGT embraces failures as learning opportunities, using each discovered defect to drive meaningful improvements. For Maritime manufacturers competing in global markets, this methodology offers a proven pathway to world-class product reliability.

The Fundamentals of Reliability Growth Testing

Reliability growth testing is built upon the premise that product reliability can be systematically improved through a structured test-analyse-and-fix (TAAF) cycle. This approach differs fundamentally from reliability demonstration testing, which merely verifies whether a product meets specified reliability requirements. Instead, RGT actively seeks out failure modes and drives continuous improvement throughout the development process.

Key Principles of RGT

The effectiveness of reliability growth testing rests on several core principles that guide successful implementation:

• Failure Discovery: Testing conditions must be sufficiently stressful to reveal latent defects within practical timeframes, typically accelerating failure mechanisms by factors of 10 to 100 times normal operating conditions.

• Root Cause Analysis: Each failure must be thoroughly investigated to identify the underlying cause, not merely the symptom. This analysis typically requires 4-8 hours of engineering effort per failure mode.

• Corrective Action Implementation: Effective fixes must address the root cause and be verified through subsequent testing. Industry data suggests that 15-20% of initial corrective actions require revision.

• Statistical Tracking: Reliability growth must be monitored using appropriate mathematical models to verify improvement trends and predict final reliability levels.

The TAAF Cycle in Practice

The test-analyse-and-fix cycle forms the operational heart of reliability growth testing. During the test phase, prototype units are subjected to environmental stresses, operational cycling, and accelerated life conditions. When failures occur, testing pauses while engineering teams conduct thorough failure analysis. Once the root cause is identified, corrective actions are implemented, and testing resumes with improved hardware or software.

For a typical product development programme, this cycle may repeat dozens of times. A complex electromechanical assembly might experience 30-50 unique failure modes during RGT, each representing an opportunity to strengthen the design before production release.

Mathematical Models for Reliability Growth

Quantifying reliability growth requires sophisticated statistical models that can track improvement over time and project final reliability levels. Several well-established models serve this purpose, each with specific applications and assumptions.

The Duane Model

Developed by J.T. Duane at General Electric in 1964, this empirical model remains one of the most widely used approaches for tracking reliability growth. The Duane model plots cumulative failure rate against cumulative test time on logarithmic scales, typically revealing a linear relationship characterised by a growth rate parameter (alpha).

The growth rate alpha typically ranges from 0.3 to 0.6 for well-managed programmes, with values below 0.3 suggesting insufficient corrective action effectiveness and values above 0.6 indicating exceptional programme performance. For Nova Scotia manufacturers undertaking RGT programmes, targeting an alpha value of 0.4-0.5 represents a realistic and achievable goal.

The AMSAA-Crow Model

The Army Materiel Systems Analysis Activity (AMSAA) model, refined by Dr. Larry Crow, provides a more rigorous statistical framework based on the non-homogeneous Poisson process. This model enables confidence interval calculations and formal hypothesis testing, making it preferred for programmes requiring statistical rigour.

The AMSAA model characterises reliability growth through two parameters: the scale parameter (lambda) and the shape parameter (beta). When beta is less than 1, the system demonstrates positive reliability growth. Most successful RGT programmes achieve beta values between 0.4 and 0.7, corresponding to substantial reliability improvement.

Planning Model Applications

Beyond tracking actual growth, these models serve crucial planning functions. Engineering teams can use historical data from similar programmes to establish realistic growth curves, determine required test durations, and calculate the number of test units needed. A typical RGT programme for industrial equipment might require 3,000-5,000 hours of accumulated test time across 5-10 prototype units to achieve mature reliability levels.

Test Programme Design and Implementation

Successful reliability growth testing requires careful programme design that balances technical objectives with resource constraints. For engineering firms serving Atlantic Canada's diverse industrial base—from offshore energy to aerospace components—tailoring RGT programmes to specific product requirements is essential.

Determining Test Conditions

Test conditions must stress the product sufficiently to precipitate failures within practical timeframes while remaining relevant to actual use conditions. This typically involves:

• Temperature Cycling: Ranges of -40°C to +85°C are common for industrial products, with cycling rates of 10-15°C per minute to induce thermal fatigue.

• Vibration Testing: Random vibration profiles between 5-500 Hz at levels of 3-10 Grms, depending on the intended operating environment.

• Humidity Exposure: Cyclic humidity between 10% and 95% RH to accelerate corrosion and moisture-related failures.

• Operational Cycling: Accelerated duty cycles that compress years of normal operation into weeks or months of testing.

For products destined for Maritime environments, additional consideration must be given to salt fog exposure, freeze-thaw cycling reflecting Nova Scotia's climate extremes, and the unique stresses of marine applications common throughout the region.

Sample Size and Test Duration

Programme planning must address the fundamental question of how many units to test and for how long. While larger sample sizes and longer durations yield more statistical confidence, resource constraints impose practical limits. General guidelines suggest:

• Minimum of 3-5 test units to enable concurrent testing and spare availability

• Test duration sufficient to accumulate 10-20 times the target mean time between failures (MTBF)

• Programme length allowing 2-4 complete TAAF cycles for each critical failure mode

A product with a target MTBF of 5,000 hours might require 50,000-100,000 unit-hours of accumulated testing. With five test units operating simultaneously, this translates to 10,000-20,000 hours of calendar time—approximately 14-28 months of continuous testing.

Failure Reporting and Analysis Systems

Effective RGT programmes require robust systems for capturing, categorising, and tracking failures. Each failure report should document the test conditions at failure, physical evidence observed, preliminary failure mode classification, and subsequent analysis findings. Modern failure reporting and corrective action (FRACAS) systems typically achieve closure rates of 85-95% within 30 days of failure occurrence.

Corrective Action Development and Verification

The value of reliability growth testing lies not in discovering failures but in developing effective solutions. Corrective action engineering represents the critical link between failure identification and reliability improvement.

Root Cause Analysis Methodologies

Thorough root cause analysis must precede any corrective action development. Common methodologies include:

• Fault Tree Analysis: Systematic decomposition of failure events into contributing causes, enabling identification of single-point failures and common-cause mechanisms.

• Fishbone Diagrams: Visual organisation of potential causes across categories including materials, methods, machinery, measurement, environment, and personnel.

• 5-Why Analysis: Iterative questioning technique that drives past symptoms to fundamental causes, typically requiring 4-6 iterations to reach actionable root causes.

• Physics of Failure Analysis: Engineering analysis of failure mechanisms based on material properties, stress conditions, and degradation physics.

Corrective Action Effectiveness

Not all corrective actions achieve their intended results. Industry experience indicates that approximately 70-80% of initial corrective actions prove effective, while the remainder require revision or replacement. Effective RGT programmes incorporate verification testing to confirm corrective action success before declaring a failure mode resolved.

The fix effectiveness factor (FEF) quantifies the fraction of corrective actions that successfully eliminate their target failure modes. Programmes targeting world-class reliability should achieve FEF values of 0.75 or higher. Lower values suggest inadequate root cause analysis or insufficient corrective action rigour.

Integration with Product Development Processes

Reliability growth testing delivers maximum value when integrated seamlessly with broader product development processes. For engineering organisations across Nova Scotia and the Maritimes, this integration ensures that reliability considerations inform design decisions throughout the development cycle.

Design Phase Integration

RGT planning should begin during early design phases, with reliability predictions informing test programme scope and duration. Design for reliability (DFR) practices—including derating analysis, thermal management, and stress screening—reduce the burden on subsequent RGT by eliminating predictable failure modes before testing begins.

Reliability block diagrams and failure mode effects analysis (FMEA) completed during design review provide the foundation for RGT test planning. High-risk items identified through FMEA deserve prioritised attention during RGT, with specific test conditions designed to stress critical failure mechanisms.

Manufacturing Process Feedback

Failures discovered during RGT often reveal manufacturing process sensitivities that require attention before production release. Workmanship-related failures, comprising 20-30% of typical RGT failures, indicate opportunities for process improvement, enhanced inspection, or design modifications that increase manufacturing robustness.

Collaboration between design engineering, test engineering, and manufacturing engineering ensures that RGT insights translate into production-ready designs. This cross-functional approach proves particularly valuable for Nova Scotia manufacturers serving demanding industries such as aerospace, defence, and offshore energy.

Industry Applications and Case Considerations

Reliability growth testing finds application across virtually every industry producing complex products. Understanding sector-specific requirements helps engineering teams tailor RGT programmes to their particular challenges.

Aerospace and Defence

Military and aerospace applications typically mandate formal RGT programmes complying with standards such as MIL-HDBK-189 and IEC 61164. These programmes often require demonstrated reliability growth to specified levels before production approval, with testing durations extending 18-36 months for complex systems.

Industrial Equipment

Manufacturers of industrial machinery, process equipment, and automation systems use RGT to achieve the reliability levels demanded by customers requiring minimal downtime. Target MTBF values of 10,000-50,000 hours are common, requiring RGT programmes of 6-18 months duration.

Marine and Offshore

Atlantic Canada's significant marine and offshore industries present unique reliability challenges due to harsh operating environments. RGT programmes for marine equipment must address salt spray exposure, wave-induced vibration, and the practical impossibility of field repairs during deployment. Extended test durations and severe environmental conditions characterise these programmes.

Partner with Sangster Engineering Ltd. for Your Reliability Growth Testing Needs

Implementing effective reliability growth testing requires expertise spanning test programme design, statistical analysis, failure investigation, and corrective action engineering. For manufacturers throughout Nova Scotia, Atlantic Canada, and beyond, Sangster Engineering Ltd. provides comprehensive reliability engineering services tailored to your specific product development challenges.

Our experienced engineering team brings decades of combined experience in reliability growth testing across diverse industries, from industrial equipment to advanced technology systems. We understand the unique requirements of Maritime manufacturers and the demanding environments in which your products must perform.

Whether you're launching a new product development programme or seeking to improve the reliability of existing designs, Sangster Engineering Ltd. offers the technical expertise and practical experience needed to achieve your reliability objectives. Contact our Amherst, Nova Scotia office today to discuss how reliability growth testing can strengthen your product development process and deliver the dependable products your customers demand.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.