Lecture on welded structures, risk and the law
Given by Professor Michael Burdekin FREng, FRS.
On Tuesday April 1st at the Lord Hives Suite, Rolls-Royce, Moor Lane, Derby
Summary
The design and construction of major welded structures is a very expensive exercise. Regrettably, occasionally things may go wrong, leading perhaps to contractual delays or even to a structural failure and the potential consequences of significant additional costs or loss of life.
Such problems may arise due to phenomena not experienced previously, but all too often failures are caused by known phenomena of which the parties involved were either unaware or they did not assess the risks correctly.
Professor Michael Burdekin's lecture proved extremely popular with nearly 40 people attending his presentation.
Michael started his lecture with illustrated examples of major successes with welded structures, which also happened to be some of the worlds largest and best known, such as the new Wembly stadium shown above.
To lead us into the main body of the lecture, Michael gave us an overview of RISK in the context of everyday risk assessments and provided us with a technical definition:-
Risk = Frequency of Occurrence X Consequences
A graph entitled Societal Risk Tolerability plotted Frequency of occurrences against Deaths. As would be expected the risk ranged from Negligible at the bottom level, through ALARP (As Low As Reasonably Practical) and onto Intolerable.
To further aid our understanding of Risk we were shown a graph plotting Failure Probability against Persons at Risk and a Qualitative risk matrix plotting Probability of Failure against Severity of Consequences. This latter graph was noted as being familiar to anyone that had been involved in Risk Assessments in the work place.
After giving us the background information we needed for assessing risk, Michael introduced us to the different Legal Procedures that we would be covering latter, which were:-
Mediation - Where parties meet without prejudice and an independent mediator seeks to broker a settlement.
Adjudication - Any party to a construction contract has a right to have a dispute decided by an adjudicator. This is a statutory procedure and usually concerns payments, but is far cheaper than full court proceedings.
Arbitration - An independent and impartial third party hears both sides in a dispute and makes a decision to resolve it.
Full Court Proceedings - The case is presented to a judge by barristers. These proceedings are both expensive and lengthy. Expert witnesses are usually called upon to aid the judge's decision.
Case Studies
Now that the audience were 'experts' in risk assessment and legal proceedings, we were treated to four examples of cases where 'failures' of different types occurred, leading to legal proceedings between the parties involved.
The technical circumstances underlying each of the cases were outlined together with a description of the arguments presented in the legal cases and the way in which a decision was reached by the law.
A comparison was made of the way in which risks are assessed in legal cases compared to an engineering assessment of risk as exemplified in design procedures and in project management for construction contracts.
Case Study 1 - Coal Wagons - Type of Case - Mediation
| (Typical coal train - 100 wagons, each carrying 97 tonnes of wet corrosive coal) |
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This case study, it was explained, involved the novel design of 520 wagons in 3CR12 ferritic stainless steel of 3mm thickness.
Michael set the scene by explaining that the wagons were manufactured in two batches. 400 wagons from material supplied in 6mm thickness, where two intermediate process firms cold rolled the material down to 3mm thickness and then annealed it. The remaining 120 wagons were from material supplied direct by the steel maker in the correct 3mm thickness.
We were informed that within 3 to 6 months of service operation, cracking was observed in wagons from the first batch, which was determined to be from poor temperature control during annealing.
With the aid of an Schaeffler Diagram, Michael explained how the poor annealing/cooling led to martensitic 'hard edges' within the plates and also how this affected corrosion resistance. Aided by microphotographs Michael described the weld, weld HAZ and fatigue cracking that had occurred.
So who was to blame?
Michael explained that at the mediation phase the Wagon design and manufacturing company claimed that the steel was unsuitable. The Intermediate rolling/heat treatment companies claimed that the steel quality was at fault.
Conversely the Steel manufacturer claimed that the steel was suitable for its application, was readily weldable and that the poor fatigue was due to the novel design of the wagons.
Risks and Legal Case
Michael presented the thought process of the Steel supplier who had a proprietary development process and of his concerns over the risk of adverse publicity, which could have destroyed the whole of his market.
Other parties claimed that the material was unsuitable and claimed costs for replacing all 520 wagons.
The Intermediate rolling/Heat Treatment companies were sited as being responsible for a much worse performance of the first batch of wagons and tried to put the blame on the quality/grade of steel that was selected. Others claimed that the Wagon manufacturers novel design made it inherently susceptible to fatigue and the wagons needed re-making anyway.
Wagons Outcome
Each party engaged technical consultants and expensive firms of solicitors.
Mediation hearings were held in two stages:-
- Discussions between technical experts to identify points of agreement and issues.
- Commercial discussions to identify the best way to recover the situation and associated costs.
Settlement - The first batch of wagons were remade, the wagon makers and intermediate process companies shared the main costs.
The second batch continued in service on a patch and repair basis, with the costs shared between steel supplier and wagon makers.
Case Study 2 - Bridge - Type of Case - Arbitration
Michael showed us slides of a very complex bridge structure with web plates, belly plates and cross girders, which although aesthetically pleasing, proved to be a nightmare to weld.
We were shown a picture of a cross section through a test piece weld, which was representative of the final production welds. As we were shown it sharp intakes of breath could be heard around the room, as the risks were instantly identified.
Michael explained that during manufacture, as the belly plates were inserted and welded, that ultrasonic testing started to detect extensive cracking in the web plates. This was attributed by the works to be lamellar tearing.
The designer, we were told, had not specified the Plate material and consequently the manufacturer had not ordered it with any Z quality properties. This led to the Bridge being remade with new web plates and a modified design (webs set on flange plates).
Parties Involved
The Steel fabricator claimed the design was impossible to fabricate and claimed for additional work in carrying out the repairs.
The Main contractor claimed substantial additional costs for delays to the project.
The Client claimed that the contractor had accepted the design and therefore counter claimed penalty costs for late completion.
Risks and Legal Aspects
Michael explained that the Fabricator did not query the design or material adequately at the time of the tender, as he thought he would not win the contract.
The Architects and Design Engineers had little practical experience of welding engineering and did not understand the risks of lamellar tearing.
The Arbitrator decided that the Fabricator had accepted the contract on the basis of the original drawings and under the Specification was responsible for the design of welded joints.
All claims were refused.
Case Study 3 - Offshore Pipeline - Type of Case - Full Court Proceedings
This case it was explained by Michael involved the laying of a 12-inch diameter API 5LX 60 steel pipeline between oil/gas platforms in the Liverpool Bay area. After just six weeks service the pipeline developed leaks, which were spotted by a ship in the area. Divers discovered longitudinal cracks across circumferential welds, at six length locations.
The pipes were subject to wet sour gas conditions and it was determined that the cracks were due to stress corrosion.
At each failure position, at least one of the pipes was found to be out of specification with a carbon equivalent >0.40%.
Risks and Legal Claims
The Client (Oil Company) claimed that Steelmaker had supplied material outside specification (> 0.40% carbon equivalent) and had falsified test certificates to show compliance. He claimed that this deceit was responsible for the failures.
The Steelmaker claimed that welding procedures were at fault causing hard spots in the weld root that cracked first and that subsequent failure by stress corrosion was inevitable.
Technical Case
Michael explained that investigations showed stress corrosion cracks started from hard zones in the weld root that cracked first. Some cases were found of these cracks that had not propagated to failure.
The Client's Experts carried out fracture mechanics analysis to estimate the applied stress intensity factor for pressure and residual stresses for different crack sizes at the weld root and had KISCC tests done on different Ceq pipes to show propagation would occur for Ceq > 0.40%.
The Legal Case
The Defence contested details of the fracture mechanics analyses and demanded more KIscc tests.
On the third day of the trial, the Defence produced a probabilistic analysis claiming to show that failure was inevitable for steel with Ceq in specification. The Claimant contested details of the probabilistic analysis.
Outcome
The Judge decided, on the balance of probabilities, that the pipeline did fail because of pipes with a Ceq > 0.40%, which were only there because of deceit by the defendant. The Judge decided, on the balance of probabilities that the pipeline would not have failed in any event.
The Claimant was awarded £108 M
So who were the winners - It appeared to the audience that the solicitors and lawyers gained the most from the court case and the underlying message was to reach an agreement and settle out of court, if at all possible.
Case Study 4 - Architectural Sculpture
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Parties Involved
The Client wanted a landmark sculpture to commemorate major athletics event.
The Architect won the competition with a striking concept as shown above.
The Structure measured 58 metres high with 178 tapered spikes (polygonal folded plate).
Michael explained that the Structural designer had to interpret the architect's design into a safe structure. Due to his limited experience in this type of design he used Specialists to advise on the effects of wind loading.
Architectural Sculture
It was explained that some three months after completion, on the day before the official opening, the end of a spike fell off.
Investigations showed fatigue cracks had developed from a bad 'extra' butt weld. Later, a second spike was found to have cracked from a poor longitudinal weld.
It was then revealed that the end 7-metre length of 53 spikes had been replaced during fabrication because of dimensional problems.
Replacement weathering steel in 3mm thickness could not be obtained in the required lengths so the fabricator 'made up the 7 metre length from a 2 x 3.5 metre length with an extra butt weld.
The Spikes were observed to vibrate in relatively low wind speeds, which was thought to be vortex shedding. After the first failure, additional dampers were fitted.
Risks and Legal Aspects
Due to the unique novel structure the client insisted on warranty bonds from the architect, structural designers and contractors.
The Structural designer was not confident about being able to predict the effects of wind and engaged specialist advice.
The specification was NSSS, which is normally used for building structures (no fatigue).
The drawings required full penetration butt welds.
Legal Cases
After the second failure, the client engaged independent consultants and claimed damages against architect, structural designer and the contractor.
Each party cross-claimed against the others. The main structural designer claimed against the specialist wind consultants for failing to advise on risks of vortex shedding and the need for dampers.
All of the parties agreed that something had to be done. A Mediation hearing led to agreement on a potential remedial solution, which was to remove the end 7m length from all spikes and replace by new lengths with mechanical spigot/socket type clamps. However, the parties could not agree how the costs should be shared. The client instigated Court proceedings.
Risks Involved
All parties knew that the Client would win if the case went to Court, but they had to assess the risks of how any award would be made up. In the mediation discussions, each party was trying to limit any contribution they made to their view of the risk if they lost the Court case.
Sculpture Outcome
The Client is considering a settlement to cover costs, which are held up by confidentiality discussions and the latest spike failure. The costs are likely to be covered by professional indemnity insurance. Repairs/remedial work to the sculpture are still to be carried out.
Conclusions
- A degree of risk is inherent in any major (welded) construction project.
- Although there are occasional structural failures involving safety, most problems arise because the project is late or fails in a way that costs the client money.
- Clients expect value for money and compliance with contract.
- There are several potential legal routes to resolve disputes - the law is well able to understand complex technical issues in sufficient detail to decide key issues.
- The law will decide on balance of probabilities.
- Expert witnesses are critical in legal cases.
Michael closed his very interesting lecture with an enthusiastic question and answer session.
By Alan Caborn
Copyright © 2008 TWI Ltd