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What is Fitness for Service? – Definition and Evaluation

What is Fitness-for-Service?

Fitness-for-Service (FFS) (also referred to as Fitness-for-Purpose) is an assessment that is carried out using the best-practice industry standards. The FFS assessment evaluates the structural integrity of an asset/component to determine whether the asset/component is suitable for its intended use. The Fitness-for-Service (FFS) assessment provides a quantitative measure of structural integrity and is part of asset integrity management. The assessments are used to highlight the need for replacement or repair of assets/components.

What are the Benefits of Fitness-for-Service?

  • Fitness-for-Service can be applied throughout many stages of an asset’s life including design, fabrication and operation
  • It can be used for plant life management, including life extension programmes
  • It reduces the requirement for unnecessary repair and replacement
  • The assessment encourages a higher standard of safety and availability of equipment, including being able to determine equipment residual life
  • The assessment combines previous knowledge and findings to optimise maintenance and inspection 

Why is Fitness-for-Service Important?

Fitness-for-Service is important at both a low level (during screening assessments) and also at a high level. The assessment at a low level can highlight if equipment is fit for continued use when limited data is available, therefore saving both money and time repairing or replacing equipment. Higher assessment levels require more data and cost more money than lower level assessments. All levels of a Fitness-for-Service assessment are used during the/as part of the lifetime of a power plant to increase availability, reliability, efficiency and safety. 

When is Fitness-for-Service Used?

Fitness-for-Service assessments are used to assess the structural integrity and suitability of a component/asset for its intended use. This allows the process to be used to assess critical pressure components and welded structures. The process is used throughout various stages of an asset’s life, including design, fabrication and operation, to identify mitigation processes needed for the safe continued use of assets/components.

Fitness-for-Service is used within many different industry sectors, including oil and gas, power generation, chemical processing and aerospace. Examples of where TWI has carried out Fitness-for-Service assessments within these industries include:


Power generation – Pressure Vessel

Oil and Gas Industry – Piping Systems

      • A Fitness-for-Service assessment based on damage that was present was carried out by TWI on a cross-country pipeline. Click here to find out more.
      • TWI carried out a Fitness-for-Service assessment in response to a small root undercut detected in a pipeline. Click here to find out more.
      • Fitness-for-Service assessment used for a high pressure piping system after the presence of flanges were discovered. Click here to find out more.
      • TWI subsidiary, Plant Integrity Ltd (PI) used a variety of assessments including Fitness-for-Service to inspect over 5,300m of pipeline. Click here to find out more.
      • Assessments including Fitness-for-Service were carried out on an oil well for a major offshore oil and gas operator. Click here to find out more.

Fitness-for-Service Software

TWI Software offers various software that assist with fitness-for-service assessments, these include:

IntegriWISE™ – This software allows the integrity of storage tanks, pipelines, pressure vessels, boilers and high temperature equipment to be assessed. It achieves this by assessing damage mechanisms and creating ‘what if’ scenarios. To find out more about IntegriWISE™ click here.

CrackWISE® - This software helps to ensure the continued safe operation of pipelines, structures and pressure equipment by helping evaluate flaws. To find out more about CrackWISE® click here.

RiskWISE – This is an integrity management software that is used on process plants, boilers and pipelines. This software is able to process large quantities of data related to risk-based inspection techniques. To find out more about RiskWISE click here.

Membership of The Welding Institute

Becoming a Member of The Welding Institute offers you access to a range of membership benefits. These benefits have been designed to support your professional progression within your career as an engineer. Although our name suggests that we only register welding and joining engineers, we do offer membership to all engineers and therefore offer membership benefits that are suited to you. These benefits include:

Click here to view all membership benefits. 

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