Steel pipelines represent today the most important infrastructure for transport of oil and gas to onshore facilities in Norway and Europe. Up to now, subsea pipeline tie-ins and repair have been carried out with the assistance of divers. The recent trend is that oil and gas are explored at deeper waters which impose an extreme challenge for both weld repair and hot tapping. It has been decided that diver assisted operations will not be used below 180 metre sea depth. This means that fully automatic remote ly controlled welding equipment must be developed if welding becomes the chosen joining process.
In the present project, basic knowledge will be built to be able to carry out future deep water repair welding and hot tapping, incorporating education of 2Ph Ds. The project will consist of 5 different tasks: (i) Study of welding process at deep waters (high chamber pressure), (ii) Requirements and possibilities for heating (including preheating), (iii) Weld modelling, with different joint configurations, incl uding wall thicknesses, welding parameters, cooling conditions, restraint intensities and residual stresses, (iv)Modelling of hydrogen pick up and diffusion during welding and possible subsequent post heating, and (v) Structural integrity and acceptance c riteria.
The hot tapping is considered to impose heavy restraining with imminent risk of cracking during or after welding. Therefore, modelling is regarded very useful, with model validations based on experimental measurements of simpler geometries at 1 b ar.
Finite element models will also be developed including heat distributions in various geometries, transformation behaviour, hardness, residual stresses, hydrogen pick up and diffusion and cold cracking susceptibility.
The involvement of PhD studies all ows more detailed study of selected areas in hyperbaric welding. This is, in fact, the first possibility to educate PhD students in Norway related to the area of hyperbaric welding.