The DNV laboratories are a valuable tool used by DNV in two vital ways: verifying theoretical models in full-scale tests and to aid in failure investigations.
DNV has a broad range of laboratories. These facilities have given DNV hands on experience of components and failure modes which have proven to be of great value to DNV's customers and to DNV's efforts to classifying ships and offshore units, create standards, and recommend effective practices and classification rules. "These resources add value to our range of other services and have provided a unique knowledge basis for a lot of the other work we do," states Elisabeth Torstad, the head of the DNV deepwater technology and technology qualification. *
Research into LNG tanks
A particular successful example of how the laboratories are used is the recent slosh testing and analyses of LNG membrane tanks. Sloshing in LNG tanks has gained increasing attention lately. This is mainly caused by developments in the LNG market, changes in the design and operation of LNG ships and an increasing interest in floating gas field exploitation.
To study sloshing loads in partially filled LNG tanks, irregular sloshing experiments have been conducted for head and beam seas for different filling levels and sea severities. A 1/20 scale model of a tank from a 138,000 m3 membrane type LNG ship was used for the tests. Measurements have been conducted using pressure transducers and pressure transducers mounted in clusters.
Step-by-step procedure
The issue of sloshing in partially filled tanks is relevant for spot trading and the offshore loading/offloading of LNG ships as well as for FPSOs with LNG capacity. DNV has developed a step-by-step experimental procedure to determine sloshing loads for structural analysis of the insulation system and tank support structure. Of key importance for a reliable evaluation is the step-by-step approach, putting emphasis on an accurate treatment of every step. This means careful modelling of operational and environmental conditions, accurate ship motion calculations, a well-defined procedure for identifying design sea states, a proper experimental set-up and an accurate treatment of the statistics involved in every step in order to determine reliable and realistic design sloshing pressures.
Valuable laboratory testing
"Much of our work is mainly based on the calibration of design formulations performed through testing," says Torstad. "Several 'cutting edge' projects and services are based on the combination of testing/practical knowledge and theoretical expertise." She mentions several examples where laboratory testing has been valuable, including the development of methodology for fatigue analyses of FPSOs. "Without this project, sufficient fatigue life of the Kizomba A and B could not have been documented," she says.
The sand management services - a recent successful cooperation between DNV Software and DNV Consulting - is based on work completed in the process laboratories. The Garn West project for Shell is another project where actual confirmation of design input through testing has been essential.
Failure investigation to find the answer
Through advanced laboratory testing and failure investigation, DNV also obtains valuable knowledge about failure modes and mechanisms with regard to how things fail and why.
Over the years, DNV's laboratory has obtained worldwide recognition for its failure investigations, covering a broad range of issues, from major breakdowns to minor damage to individual components.
"The main goal for a failure investigation is to prevent new failures, increase safety and optimise operations," says Trude Helgesen, head of section.
Failure investigation is not a clearly defined term, but it typically includes the collection of data and information, visual examinations, photo documentation and material verification. DNV has acquired extensive experience and knowledge through working with a wide range of clients and services. This has also given the company broad knowledge of the industry and the regulators. A combination of DNV's risk management expertise with technical knowledge has made this a highly valued service.
"Due to the failure aspect, a major part of this service is contract work and very often of a confidential nature," says Helgesen.
Borealis - a close relationship
Olaf Andersen, chief engineer in material technology responsible for all of Borealis's mechanical equipment, has had a long, close relationship with DNV as a user of DNV services. With a degree in physical metallurgy from the Norwegian Institute of Technology (now the University of Science and Technology) in 1970 and two years spent as a scientific and research assistant to Almar Ness, he came to Stavanger Staal in 1972. There he learned about metallurgy the hard way as quality control manager - and also helped create some alloy developments himself.
"Five years here was an extremely good school," he says. So when petrochemicals came to Norway, he jumped on this bandwagon and started to work for Statoil in 1977. When Borealis was established in 1994, he had been chief engineer responsible for material technology at Statoil headquarters since 1991. In 1998, he started to work for Borealis, where he now spends half his time on group issues and the other half troubleshooting at Borealis' facilities worldwide.
Expertise and equipment
"We've used DNV to develop our risk-based inspection system - and we use DNV to inspect damage. The DNV laboratories have a reasonable amount of staff and are flexible and able to agree to and deliver an inspection reasonably quickly. They have expertise and equipment and we use them wherever this is practically possible and sensible."
DNV has supplied NDT services to the facilities at Bamle in Norway for the past 30 years. Borealis has now also entered into a framework agreement with DNV regarding certification throughout Borealis. Andersen also points out vibration studies of structures and pipelines carried out by Borealis and DNV in collaboration, supported by funds from the Research Council of Norway. Several surveys have also been conducted relating to corrosion in steam systems, and dynamic steam boiler simulations have been carried out at one of the plants.
Borealis currently has 5,000 employees. Statoil owns 50 percent of its shares, while OeMV in Austria and IPIC - a fully owned subsidiary of Adnoc, Abu Dhabi's national oil company - own 25 percent each. Borealis is a major manufacturer of pipe materials, high-voltage insulation, engineering applications and plastics for cars and household articles. The company has facilities in Norway, Sweden, Finland, Germany, Austria, Italy, Abu Dhabi, China and the USA.