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Standards for High-Integrity Structures

TWI is actively involved in committees governing a large number of international standards, including several which apply to high-integrity structures. The insight gained from this participation is shared with Member companies.

High-integrity structures can be considered as those for which the consequences of loss of containment and/or failure would be very severe: pressure vessels and piping, pipelines, cranes, bridges, storage tanks and steel-framed buildings to name just a few examples.

Design, fabrication, inspection and operation of high-integrity structures are central to the business of many of TWI’s industrial and professional Members. Consequently, TWI has long been involved in developing and maintaining the relevant national and international standards on their behalf.

While TWI plays a role in over 120 standards committees in all, this page focuses on a selected few that are particularly relevant to high-integrity structures.

High-integrity structures standards

BS 7910: 2013 Guide to methods for assessing the acceptability of flaws in metallic structures

This standard is published by BSI in the UK but used worldwide in the design, manufacture, operation and analysis of high-integrity plant and structures, especially in the following industry sectors:

  • oil, gas and chemicals
  • fossil and renewable energy
  • construction and heavy engineering.

Failure/damage mechanisms addressed in BS 7910:2013 include fracture, fatigue, plastic collapse, creep and general corrosion.

BS 7608: 2014 Guide to fatigue design and assessment of steel products

This standard addresses the design and assessment of steel structures, typically in the welded condition, in which fatigue may initiate at stress-concentrating details such as the weld toe. In contrast with BS 7910, which is based on fracture mechanics concepts, BS 7608 assumes that the structure or product is nominally free of flaws.

R6 Assessment of the integrity of structures containing defects, Revision 4

The UK nuclear industry has developed and maintained its own defect assessment procedures (in particular R5 for high-temperature damage and R6 for fracture avoidance) since the 1970s. TWI is a member of the R6 panel, contributing both via an annual programme of research work relevant to the R6 procedures and through participation in committee processes.

API 579-1/ASME FFS-1, 2007 Fitness-for-service

In the USA, API and ASME have developed a fitness-for-service procedure, covering a wide range of failure and damage mechanisms. TWI is a member of the committee, contributing via its North America office.

API 580/581

API 580 and 581 (Risk-based inspection) allow in-service inspection to be better focused by concentrating on areas of plant in which the probability and/or consequences of failure are highest. TWI is represented on this committee.

RCC-M and UK user group

The French AFCEN RCC-M code provides a design basis for nuclear island components. TWI’s involvement with the code includes membership of the committee, and leading a UK user group which provides a communication channel between AFCEN and code users.

PD 5500 and EN 13445

TWI is also a member of various committees and sub-committees charged with the development and maintenance of standards/guidance documents for pressure vessels, both in the UK and at European level.

Benefits to TWI members

Standards and standards bodies differ enormously in their engagement with end users – for some standards there is a system of code cases or enquiry cases, whilst for others publication is preceded by a Draft for Public Comment (DPC). Finally, there is the option of direct participation in the committee.

While TWI members are free to pursue all of these avenues, they have the additional advantage of being able to communicate directly and in confidence with TWI staff who are involved in committees to discuss issues such as:

  • the background to, and interpretation of, certain clauses
  • amendments to existing standards
  • the need for new standards. 

These discussions do not, of course, undermine the role of the relevant standards committee, each of which has its own protocol regarding representation and transparency.

TWI is in the process of appointing a Standards Development Programme Manager who will provide a single point of contact with members on issues connected with standards.

For more information please email:


contactus@twi.co.uk