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Fatigue Testing of Steam Generator Materials

Near Threshold Fatigue Crack Growth Rate Testing

Introduction

In the US alone, material degradation problems due to Environmentally Assisted Degradation (EAD) - Fatigue, Corrosion Fatigue (CF), and Stress Corrosion Cracking (SCC), have cost the nuclear industry at least $10 billion in the last 30 years because of forced and extended outages, increased inspection requirements, component repairs/replacements, and increased scrutiny by the regulator. As designs demand higher performance and longer lives—up to 80 years proposed--incidences of environmentally assisted degradation will increase. Plant modifications and upgrades, compliance with new regulatory standards, and requirements that designs account for fatigue, are driving the need for fatigue testing. 

As Alloy 800 is being considered as a material of choice for new designs, testing in representative CANDU environments and US PWR and BWR environments is required. Currently, there is little information on Incoloy 800 (Alloy 800) in CANDU primary water, or in environments representative of secondary side crevices. 

 

Fatigue and Corrosion Fatigue Issues

 

Fatigue cracking is a common failure mechanism for many nuclear power plant components, including steam generator tubing materials under conditions of flow-induced vibration with chemical interaction. Data for flaw growth rates, including fatigue cracking and corrosion fatigue cracking, are key inputs to validating fatigue crack growth models, fitness-for-service assessments, and projecting future behavior. 

 

Kinectrics Solution

Near-threshold fatigue crack growth rate tests on chemically and microstructurally representative steam generator materials were performed under air and simulated crevice environments using different fatigue testing variables.
 

Scope of Work

 
  • Manufacturing to obtain chemically and microstructurally representative SG materials
  • Tests performed according to ASTM E647 with DCPD crack length monitoring
  • Decreasing DK under Constant R (load ratio) and Constant stress intensity Kmax at frequency between 10-30 Hz.
  • High (R = 0.7) and low load ratio (R = 0.1) to assess crack closure effects
  • Room temperature air, elevated temperature air (300°C) and elevated temperature neutral crevice environment (300°C)
Additional Capabilities:
  • Environmental chamber for high temperature air testing up to 595°C
  • Corrosion fatigue testing at frequencies <1Hz in aqueous pure water and crevice environments up to 320°C.  
Results 
 
Threshold plots illustrating the relative effects of load ratio, temperature, and environment on threshold stress intensity were determined and, data derived for use in unified fatigue crack growth rate models to improve SG tubing fitness-for-service assessments.

About This Case Study

Industry Sector

  • Generation

Generation Type

  • Nuclear

Nature of Service

  • Testing - Lab Services

Client Assets

  • Steam Generators

Kinetrics Facilities

  • Decontamination and Refurbishment Facility
  • |
  • Radioactive Materials Laboratory
  • |
  • Materials Testing and Structural Integrity

Tags

  • CANDU
  • |
  • Stress Corrosion Cracking
  • |
  • i
  • |
  • ASTM 647
  • |
  • Corrosion Fatigue
  • |
  • Fatigue testing