Subscribe to our newsletter to receive the latest news and events from TWI:

Subscribe >

Guidelines on fatigue life of ageing pressure vessels

In various industry sectors there are a number pressure vessels, still in use after many years of operation, that were originally designed to now outdated codes and whose remaining fatigue life is unknown. TWI has produced guidelines, published by the Energy Institute, to assist plant engineers in determining the risk of fatigue failure of their vessels and remaining fatigue life. Subsequently, this will enable plant engineers to plan targeted, cost efficient inspections for those vessels most at risk.

Overview

The published guidelines describe a process for screening vessels according to their risk of fatigue failure and provide a worked example of applying the process.  Where the need for an assessment of remaining fatigue life is established, the guidelines describe how this can be done, and the use of inspection and other options available when the design fatigue life is reached.  The guidelines also present studies made by two offshore operating companies assessing the risk of fatigue failure of their ageing pressure vessels (Figure 1).

Objectives

  • Highlight the factors that are known to increase the risk of fatigue failure of pressure vessels
  • Provide advice on the assessment of remaining fatigue life using modern analysis methods
  • Give options on how to extend design fatigue life.
Figure 1. Pressure vessel from the 1970s
Figure 1. Pressure vessel from the 1970s

Fatigue risk factors

Factors increasing the risk of fatigue failure are summarised in Figure 2.  Welds are particularly susceptible to fatigue and should receive the most attention. In general, the presence of several concurrent risk factors should be a trigger for assessing fatigue in more detail.

 

Remaining fatigue life

The need to undertake an assessment of the remaining fatigue life of a pressure vessel will vary, depending on the context and company policy. Generally, it would be good practice to assess vessels where:

  • High risk of fatigue failure has been assessed
  • No previous assessment of fatigue is available
  • A design fatigue usage factor limit is reached
  • Life extension beyond design is required
  • Fatigue cracks have been detected in service.

 

Remarks

These guidelines are due to be published and will be made openly available from the Energy Institute by the end of 2019.

Figure 2. Summary of key factors leading to increased risk of fatigue failure
Figure 2. Summary of key factors leading to increased risk of fatigue failure
Avatar Emilie Buennagel Principal Project Leader - Fatigue Integrity

Emilie joined TWI in August 2010 after spending more than three years in the engineering and technology division of a large materials testing company in the UK. Previously she completed her MSc studies at the University of Orleans in France, including two work placements at Nexans in Germany.

Emilie brought to TWI experience of mechanicals testing and metallurgy, primarily for the aerospace industry. In her previous employment she was responsible for managing projects and developing new test programmes. At TWI she manages a range of projects, including failure investigations, fatigue assessments and resonance fatigue testing of full-scale pipe.

Among the research projects Emilie has been involved with has been a core research programme investigation comparing approaches to design fatigue assessment, with reference to a pressure vessel designed to an old standard. A published paper based on this research is available on the TWI website.

}