Remaining Life Assessment

Remaining Life Assessment (RLA)

& Condition Assessment of Boilers

TCR has developed expertise in assessing the current condition of boilers and also their remaining life. TCR undertakes both Level–II assessment and Level-III assessment for RLA. TCR adopts a pragmatic approach and efforts are directed towards collecting data on the component/equipment history in addition to interviewing external experts familiar with the operation details. All the details are evaluated vis-à-vis the testing and studies are conducted at a later stage using either a:

CALCULATION BASED APPROACH: Calculation procedures are often employed to determine the expanded lives of components under creep, fatigue and creep-fatigue conditions. From plant records, information about temperature and cycling history is gathered and using the standard material properties and damage rules, the fractional life expanded up to a given point in time can be estimated.

DESIGN APPROACH: Components which operate under creep regime are generally designed on the basis of yield, tensile and fatigue strength along with a focus on suitable safety factors. Under normal conditions, deformation and fracture are not time dependent. As long as the applied stresses do not exceed the design stresses, these components should last indefinitely; but in practice, various factors cause the reduction in life.

TCR Advanced Approach
Approach to

Remaining Life Assessment​

  1. Understanding the actual degradation mechanism
    • High Cycle Fatigue
    • Low Cycle Fatigue
    • Thermal Fatigue
    • Thermo Mechanical Fatigue
    • Thermal Aging
    • Wear
    • Creep
    • Embitterment
    • Corrosion
  2. Visual Examination Of Physical Properties
  3. NDT involving In-situ Metallography, Ultrasonic Testing, Magnetic Particle Inspection, DP Test, Ferrite Measurement
  4. Stress analysis: To know the strength of the material and check ruptures
  5. Non-Destructive Testing: To provide an insight into the component integrity
  6. Laboratory Testing: To provide valuable information about the material soundness
  7. Judgment of Fitness of the Equipment: Based on available data
  8. Suggestions on Repairs: If required, repair of the equipment is suggested for life extension
  9. Judgment of Remaining Life Based on Analysis: Estimates for remaining life is carried out. In addition to this, periodic inspection procedures are spelled out to monitor the health of the equipment during the course of operation.

If the results reveal an operational mistake, restriction in free movement by thermal expansion or any other prevailing damage mechanism, then a preventive maintenance approach is formulated. RLA is done based on life-limiting factors like corrosion, creep and microstructure degradation with respect to time. There are different approaches available to assess the remaining life based on thermal cycles, creep calculation and fatigues cycles. Based on these aspects, the remaining life is ascertained by integrating the rate of degradation v/s available material properties.

Definition of Component Life
  • History-based criteria: 30 to 40 years have elapsed, statistics of prior failures indicate impending failure, the frequency of repair renders continued operation uneconomical, calculations indicate life exhaustion

  • Performance-based criteria: Severe loss of efficiency indicating component degradation, large crack manifested by leakage, severe vibration or other malfunction, catastrophic burst

  • Inspection- based criteria: Dimensional changes have occurred, leading to distortions and changes in clearances, inspection shows microscopic damage, inspection shows crack initiation, inspection shows a large crack approaching the critical size

  • Criteria based on Destructive evaluation: Metallography or mechanical testing indicates life exhaustion