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What is Structural Integrity and Why is it Important?

   

What is Structural Integrity?

Structural integrity is an engineering field that plays a fundamental part of ensuring that structures are fit to do what they are designed (fit for purpose) under normal operational conditions, and are safe when conditions exceed the original design intent. This includes supporting its own weight. Its aim is to prevent deformation, breaking and catastrophic failure of a structure due to load, allowing the structure to perform its duty reliably (being whole and undivided) throughout its predicted lifetime.

Integrity is not just a case of good design; it needs to be maintained for the life of a structure. This requires inspection and maintenance at periodic intervals. Engineers ensure structures are safe, reliable and perform their designed function throughout their lifetime.

What are the Causes of Structural Failure?

Structural failure can occur from a range of different sources. The type of failure is often associated with the industry, environment and application of the structure. The primary reasons for failure are as follows:

  • Weak structures. The structure is not strong enough to withstand the load to which it is subject. This is usually due to inappropriate geometric design or material choice
  • Structural deterioration. The structure deteriorates due to corrosion, fatigue, wear, rot or creep. Fatigue failures often begin when cracks form at regions of high stress. These cracks grow when subject to cyclic loading, resulting in sudden failure. This is usually due to inappropriate geometric design, material choice or maintenance
  • Manufacturing errors. This includes using the wrong materials or not following manufacturing procedures or standards. It can also result from poor workmanship or components being out of tolerance, etc
  • Defective material. The materials don't conform to standards, resulting in a lower load bearing capacity than designed.
  • Improper environmental considerations. Engineers may neglect mitigating features for certain environmental conditions, such as natural disasters
  • Improper operational conditions. The structure is not used for its intended purpose

At What Temperature Does Steel Lose Structural Integrity?

Structural steels are used in most large construction projects, such as buildings and bridges, in the form of girders etc. The performance of the steel is vital to maintain the required integrity. High temperatures are known to weaken steel, which begins to soften at around 425°C and loses about half of its strength at 650°C. At these temperatures, the steel will begin to buckle and twist if subject to high loads, which will impede structural integrity.

Consequently, engineers must take into account the environmental temperature range that a structure will be subject to over its life span.

How to Calculate the Integrity of Structures

Engineers combine an array of considerations into the design process, such as materials performance, stress analysis and fracture mechanics.

Once built, a construction will need inspection and maintenance to maintain its integrity. To do this, an engineer might:

  • Carry out inspections to identify damage. This might involve the use of non-destructive testing (NDT)
  • Check that a structure has been built according to the appropriate designs, procedures and standards
  • Check that a structure is being used appropriately for the environment designed for
  • Recommend and design modifications to address areas of concern

Addressing Structural Integrity

TWI has a long history of working with its Members, across a range of industry sectors, to assist in maintaining assets. Discussed below are examples of these collaborations.

TWI collaborated with a major Oil and Gas operator to provide a comprehensive structural integrity assessment of around 100 oil well conductors, to ensure they were safe to continue service, providing peace of mind to the Member company. TWI also provided the operator with an inspection strategy for the future, to ensure the most efficient use of resources and reduced inspection costs going forward.

TWI’s expertise was called upon as part of a consortium of partners working on the ASPIRE Project, co-funded by the Horizon 2020 programme of the European Union, to ensure the integrity of critical components for upstream assets. Due to life extension projects, many oil wells are being used beyond their original design life, which makes the assessment of critical components more important than ever to prevent unexpected failures. Once the assessment is complete, the operator can use ASPIRE to determine risk targets based around the probability and consequence of failure and a recommended time until inspection is required.

Collaborating with a Member company, TWI used its expertise to assess the Douglas Platform complex in the Liverpool Bay / Irish Sea. TWI’s engineers demonstrated that the crack-like flaws observed in the structure would not impede performance, with respect to failure by fatigue and fracture, over the next 30 years (the design life of the platform). The integrity of the asset was assured without repair.

Owing to TWI’s dedication to its Members’ needs, TWI was involved in the foundation of The Structural Integrity Research Foundation (SIRF), which was founded in 2012 in collaboration with BP and the Lloyd’s Register Foundation. The aim of the foundation is to ensure that university research into issues related to integrity management align closely to the needs of industry. To achieve this, SIRF is broken down into three distinct areas – Innovation Centres to undertake research programmes in disciplines related to the integrity of structures, the National Structural Integrity Research Centre (NSIRC) a postgraduate engineering and educational facility, and Accelerated Innovation Programmes (AIPs) which conduct research and development to address the most pressing needs of TWI Members.

Related Frequently Asked Questions

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