Objective
The aim of the project was to develop further the wet welding technique achieved in a previous CF-Project (TH./09045/88) and to apply the results of fatigue studies to a structural application and to optimise the repair design. The object was the development of design criteria for a repair procedure in wet environment down to repair depths of at least 100 msw.
No knowledge existed on the effect of practised repair technique on the structure and its long term performance. The project had to evaluate these effects through theoretical and practical tests and optimization activities and elaborate new design criteria for a safe repair technique to extend the operational life time of the envisaged structures.
The results would increase the credibility of the wet welding process and should lead to the implementation of new standards and regulations for quality wet welds to achieve a recognized and certified technique to compete economically with dry hyperbaric welding.
Manual welding trials have been carried out in 6 m water depth, 20 msw, 55 msw, 55 msw and 100 msw at the N.H.C. Aberdeen.
Validation tests were completed in 72-75 m water depth at the Elf Emeraude offshore field, Pointe Noire, Congo.
Results and evaluations are presented in the Interim and Final Reports and show that the chemical and mechanical properties of weldments made with improved electrodes exceed by far the Type B qualification requirements of ANSI/AWS D3.6-93 Specification.
Fatigue testing is an approach not previously applied in wet welding and the Project trials have revealed that results from wet welding are comparable with those achieved in air and, together with the improved mechanical properties resulting from the modified electrodes, have validated the procedure and welder performance qualification which has been developed.
The Project has considerably advanced the credibility of wet welding by demonstrating improved quality expectancy, and dissemination of results has let to improved knowledge of its potential capabilities to the extent that National and International Standards are being influenced. The Contractor intends to continue in the study and improvement of wet welding in the future.
Achievement of quality welds on high Carbon Equivalent structural steels by the application of the wet welding technique even in greater water depth. Achievement of process credibility and recognition of the wet welding process and technique as a quality repair procedure.
The technology is operating in context with underwater repair by the application of the wet welding process. This process has the advantage of high flexibility and extreme mobility combined with extremely low preparation time for its offshore application. In case of a rupture of a pipeline, structural damage or other failure an environmental pollution can be reduced by rapid intervention with this process.
The general trend in offshore requirements of techniques to reduce repair and maintenance costs significantly is still existing. Hyperbaric dry welding has still achieved the highest credibility in offshore welding repair techniques but such repairs require high investments and mobilisation costs (engineering,habitat fabrication and installation). Wet Welding is a more flexible, mobile and economical welding technique. Due to the insufficient knowledge on the effects of repairs by wet welding on the structure and its long term performance confidence, credibility and working standards needed to be established before contractors and operators can engineer to enable the wet welding technique to be applied. The project had to generate necessary information and data to establish working standards and define repair weld quality and improve the necessary confidence in performance of the process and its credibility.
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DEM - Demonstration contractsCoordinator
GEESTHACHT
Germany