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

Subscribe >
Skip to content

The 50-year view of fracture

Back to Media and Events 2013-07-creepimage-inspecting-creep-damage-in-critical-power-plant-components 2016-09-cutting-edge-technology-for-nuclear-decommissioning A career in welding inspection Additive manufactured medical implants to enter mainstream Additive Manufacturing UK Strategy update available for download Advanced electron beam facilities meet advanced industrial challenges Advanced ultrasonic full matrix capture inspection software launched Armourers & Brasiers' awards open for entries Art exhibition leads to new method of laser metal deposition Asbestos detection made easier and more reliable ASME issues White Paper on auditing of welding Audit shows TWI as integral to innovation Aviation Industry Corporation of China collaborates with TWI BeamAssure™ – electron beam welding quality assurance tool Best practice for nuclear construction industry welding BS 7910:2013 - Assessing flaws in metallic structures Call for papers: 12th International FSW Symposium CII and TWI awareness seminar in composites technology Coatings and surface engineering: addressing the needs of industry Combatting ice and erosion in extreme low temperatures - EIROS Combining Cathodic Protection with Aluminium Coatings CROWN project commended for offshore wind corrosion work Depositing silicon carbide coatings by thermal spraying Digital Twin Technology to monitor offshore assets Digital twin technology wins environmental business award Dr Melissa Riley presents paper at international conference Dr Melissa Riley represents TWI at international conference eLearning package for CSWIP 3.1 Welding Inspector launched Entry is now open for SkillWeld 2016 Extending Aircraft Life Using Cold Spray Technology Fibre delivered laser beam cutting optimisation Friction stir welding – joining the future of industry Friction stir welding and Japanese jewellery Government funds £10 million technology hub in Teesside Has your PCN NDT Certification been voided? TWI Can Help… Her Royal Highness The Princess Royal opens new laboratories at TWI High-pressure hydrogen testing at TWI Ice-repellant coating for aerospace and energy industries Industry benefits of composites microwave processing Innovation Centres at TWI deliver progress for industry INTRAPID produces rapid in-line laser AM inspection systems Introducing the TWI Virtual Academy: studying on your own terms Investigating geothermal coatings for the future of renewable energy Laser scanner improves TWI weld analysis services for Members Lasers for decommissioning: the story so far Lifting the lid on innovation: exploratory projects at TWI Lord Heseltine opens new TWI technology and training centre Meeting reinvigorates Welding Institute's Liverpool branch Mike Russell appointed as TWI Operations Director 'Mind the doors' – New project investigates train door failure Mobile electron beam welds for fabricating large structures ModuLase - combining laser processes for the future of manufacturing MoU between ALFED and TWI enhances collaboration Nanosecond pulsed laser expands opportunities for project work NDT Voiding of PCN certification from NDT International New benefit for TWI Members: free access to Welding Abstracts journal New building to house TWI's structural integrity expertise New centre for Advanced Manufacturing Technologies launched New eBooks added for Professional and Industrial Members New facility for testing the barrier performance of polymers New fracture testing accreditation New Granta Centre manager guarantees premier conferencing New home and new capabilities for TWI in Middlesbrough New manufacturing process supports Hayter's winning position New sensor technology for safe shale gas extraction funded New TWI article breaks down the changes to ISO 15614-1 New ultrasonic testing courses from the TWI Virtual Academy New welding apprenticeship standards receive government approval Novel solution for submersible pumps in oil and gas industry Open Day sparks the start of a new era of research for TWI Pioneering tests being conducted on bespoke TWI rig Plant Inspection training meets need for competent workers Plastics welding experts answer your questions at Aquaculture UK 2014 Progressing graphene as a supercritical fluid barrier Project investigates Powder Metallurgy for astrospace use Purpose-built pressure testing facility opens for business at TWI Purpose-built pressure testing facility to be constructed at TWI Registration opens for TWI BS EN ISO 15614-1 (2017) training RJD Engineering gains Factory Production Control system Certification Rolls-Royce's Martin Boyd discusses the benefits of becoming an IEng Showing expertise in corrosion safety, investigation and assessment Simulating real-world conditions for oil and gas research Skills Development Fund Scheme provides extra TWI courses SkillWeld medallist goes on to take gold at EuroSkills 2016 SOCAR and TWI celebrate new competence training partnership Success for TWI's first blended learning course candidates Successful engineers graduate from EWF/IIW Diploma in Welding 'SUPERSLAB' to meet thicker high-strength steels challenge SurFlow: secure, robust, integrated data transfer through composites Symposium highlights developments in linear friction welding Taking the next step as a CSWIP Welding Inspector Tate Modern use solvent technology for art restoration Teletest business transfers to Eddyfi Technologies The 50-year view of fracture The Transport Systems Catapult and TWI Announce Partnership The Welding Institute Annual Awards and Dinner 2017 The Welding Institute Awards 2018 – Applied Technology Award The Welding Institute promoting career development at NECR exhibition True Stress-True Strain Tensile Testing to Failure TWI and Lloyd's Register launch Fullagar Technologies initiative TWI and Lloyd's Register projects advance take-up of AM TWI celebrates National Women in Engineering Day TWI CEO Christoph Wiesner awarded OBE TWI combines heritage with innovation for the Morgan Motor Company TWI commence 'SubSeaLase' decommissioning project TWI delivers plastics welding training course to Fusion Marine TWI develops essential metallography training to ensure best practice TWI enters research centre agreement with AECC BIAM, China TWI helping UK businesses to 'Access India' TWI helps bring Philips Avent's thermoplastic nebulizer to market TWI helps Engineering College meet industry demand for staff TWI holds successful cold spray technology course TWI hosts graduation ceremony for EWF/IIW Diploma engineers TWI joins 'Integral' nuclear waste project TWI lands NDA innovation award for nuclear decommissioning TWI launches course for advanced digital radiography TWI pioneers 'invisible weld' process TWI Pioneers New Dissimilar Weld for European Space Agency TWI rewards outstanding undergraduate engineering projects TWI signs Memorandum of Understanding with Saudi Aramco TWI Supports Underwater Laser Cutting Project TWI Technology Fellow given Visiting Professorship at LSBU TWI Training success story - Vera Dragoi TWI wins RIBA Awards TWI working to progress composites in the automotive industry TWI's Dr Philippa Moore: A role model for female engineers TWI's Dr Shiladitya Paul called as guest editor of Coatings journal Ultrasonic imaging climbing robot passes field trials Update on CPD for Welding Institute Professional Members Vince Cable India visit promotes UK business successes Welding Institute Annual Awards 2018 Welding Institute's latest Engineering Council registrants Welding the unweldable: TWI friction stir welds ODS steel WindTwin project to revolutionise wind turbine technology Workshop to address dissimilar materials joining challenge World's largest linear friction welded component produced World's most precise weld made at TWI
 
20 November 2015

It's been 50 years since a large steel pressure vessel fabricated in Wolverhampton exploded during hydro-test just before Christmas in 1965, throwing a chunk of steel the size of a car through the wall of the factory[1].

By a miracle no one was seriously injured, but TWI led the investigation into what caused the catastrophic brittle fracture that day. A large piece of that failure has been kept at TWI since the accident, serving as a memory of what can go wrong when lessons of fracture avoidance are not learned. You can see it still, standing in the atrium at TWI's Cambridge office.

The mechanism that sank the Titanic

Fifty years before the explosion of that pressure vessel, it had been another high-profile failure that had made the headlines: RMS Titanic. Only recently have engineers understood the role that the brittle fracture of materials played in the sinking of the Titanic on April 14 1912[2].

When the iceberg struck the hull of the Titanic, it was at high speed, and at low temperature (around 0°C). It is known now that the rivets and the hull steel had very low impact toughness, based on testing pieces of hull recovered from the seabed in the 1990s.

Low temperature, high loading rate and low toughness: a classic combination for brittle fracture. However, investigations at the time focused only on improvements to ship design and safety procedures, since, without an understanding of the fracture behaviour of metals, they could not seek to improve them.

Although the Charpy test to characterise material fracture behaviour was first described around 1900, it was not until the Second World War that the benefit of fracture testing was realised in earnest.

The birth of fracture mechanics

This time, it was the Liberty Ships, being built by the USA using welding instead of riveting to reduce ship production time from months to just 42 days. This was a significant contribution to the war effort and Allied victory, but a small number of the 2710 Liberty ships that were built between 1941 and 1945 suffered significant brittle fractures in the hulls; some even broke in half. Major effort in the USA and the UK was put into understanding the causes of these failures[3], bringing with it the true dawn of industrial fracture mechanics.

But by the time of the Wolverhampton incident in 1965, it had been over two decades since the Liberty Ship fractures had started the academic discussion about brittle fracture and fracture mechanics of steel structures.

At Cambridge University's engineering department, Constance Tipper, working with Prof (Lord) Baker, had written in the 1950s about the ductile-to-brittle transition of steels and the role that welds can play in making brittle fracture more likely[3].

Early research at TWI

In 1951 Baker had encouraged another of his research students, Alan Wells, to go and work for BWRA (as TWI was known then), and develop the understanding and testing of brittle fracture in thick section welded steel. Wells subsequently became well known for inventing the CTOD (crack tip opening displacement) concept of fracture, which he first described in 1961.

Therefore, at the time of the pressure vessel failure all those years ago, there was still no standard for fracture toughness tests, there were no fitness-for-service assessment procedures, and the understanding of fracture mechanics concepts such as CTOD was in its infancy.

Nonetheless, the fabricators should have known how to avoid hydrogen cracking in the welds; they could have performed Charpy testing, and ought to have ensured better control of the post-weld heat treatment in order to avoid catastrophic failure that day.

The BWRA report into the failure recommended using fracture mechanics principles to provide acceptance criteria, and to ensure hydro-testing was done above the ductile-to-brittle transition temperature[1]. Good advice to this day.

Lessons learned

In the decades since, failures like that pressure vessel have become extremely rare, certainly in the developed world, and not just because the litigation surrounding modern failures restricts the publicity around possible cases. No. Brittle fractures occur far less frequently because we have been learning the lessons over time about how to avoid them.

These lessons are now so firmly embedded in modern design codes and acceptance standards as to have become common knowledge. Post-weld heat-treat thick sections; meet certain Charpy requirements when low temperatures will be experienced; do not permit cracks in welds. Obvious.

Failures in recent decades seem more likely to be caused by corrosion damage, or by operator or procedural error (such as Piper Alpha or the Buncefield oil fire), rather than as a consequence of the behaviour of the welds and materials in service.

However, while materials from the 1960s remain in service they can still be susceptible to brittle fracture, as has been experienced in the USA with some fairly recent failures of vintage gas transport pipelines.

But as industry moves towards the rote-learning of these fracture-avoidance truths, are we at risk of becoming complacent that we have 'solved' brittle fracture?

Engineering critical assessment provides a technique to calculate the likelihood of fracture, even without the design code rules. Perhaps brittle fracture has gone away and we can stop worrying about it? But the more our understanding of fracture is seen as 'common knowledge', the less commonly understood that knowledge seems to become.

Risks from complacency

The Hatfield rail crash in October 2000 was due to pre-existing fatigue cracks which caused a brittle fracture of the rail[4]. The track operator had found the crack nearly two years before the crash and scheduled a replacement rail.

They should have known the risk that the cracks posed for causing brittle fracture of the rail, but they didn't understand the urgency and importance of replacing it, and failed to manage effectively the work of the track maintenance contractor. In addition, the track maintenance contractor failed to manage the inspection and maintenance of the rail at the site of the accident effectively and in accordance with industry standards.

The crash from the derailment of the train resulted in four passenger fatalities, over 70 injuries, and a manslaughter trial against six rail executives and their companies. The case highlighted the failings in the corporate knowledge of the condition of the railway tracks, and led to a huge programme of track repairs.

Two years after Hatfield, The Institute of Rail Welding was founded by The Welding Institute to help prevent further accidents through lack of understanding.

Today, if we become complacent about brittle fracture, we risk relearning the ignorance of last century. Today it is our responsibility to keep in mind the lessons of the past, not just for our business success, and technical reputations, but to save the lives of people who may needlessly die in horrendous accidents that brittle fractures can cause.

Continuing to inform industry

TWI has spent the last 50 years progressing the knowledge of fracture testing and assessment by the hard work of generations of its engineers. By sharing this knowledge and experience with our Industrial Members through projects, research and training, they too can keep ahead of current challenges in fracture. And this work continues to this day with TWI engineers continuing to lead the development of national and international standards for fracture testing and assessment.

Postgraduate research through the National Structural Integrity Research Centre[5] is investigating the validation of the CTOD concept to alloys other than structural steels, and the effect of a sour environment or high strain rate loading conditions on the fracture behaviour of modern steels, amongst numerous other integrity research topics.

Meanwhile TWI's Industrial Members also continue to seek out fracture knowledge, with fracture-related articles being amongst the most popular from TWI online. In this way it is hoped that no TWI Member will suffer the consequences of fracture complacency. Fracture is still as important today as it has been for the past half a century. And as for the next 50 years? I can't wait to find out!

Written by Dr Philippa Moore CEng FWeldI
Team Manager, Fracture Testing and Materials Characterisation

References:

  1. 'Investigation into the failure of an ammonia converter by brittle fracture', by F M Burdekin and T Boniszewski, BWRA Report, 1966.
  2. 'The Royal Mail Ship Titanic: Did a Metallurgical Failure Cause a Night to Remember?' by Katherine Felkins, H.P. Leighly, Jr., and A. Jankovic, JOM, 50 (1), pp. 12-18, 1998.
  3. 'The brittle fracture story' by Constance Fligg Elam Tipper, Cambridge University Press, 1962.
  4. 'Train derailment at Hatfield: A final report by the independent investigation board, Office of Rail Regulation, July 2006.
  5. The National Structural Integrity Research Centre, NSIRC, (http://www.nsirc.co.uk/) founded in 2013.
Part of the pressure vessel failure from 1965 which landed in the car park of the Wolverhampton fabricators
Part of the pressure vessel failure from 1965 which landed in the car park of the Wolverhampton fabricators
The piece of the brittle fracture preserved at TWI, being shown to Princess Anne in 2015
The piece of the brittle fracture preserved at TWI, being shown to Princess Anne in 2015
The Wells wide plate test replicated brittle fracture conditions seen in service, in the laboratory
The Wells wide plate test replicated brittle fracture conditions seen in service, in the laboratory
Repairing railway track
Repairing railway track

For more information please email:


contactus@twi.co.uk