| dc.description.abstract | The second part of XX century has taken a large part of Oil & Gas production to the offshore. The processes and equipment used inland, had to be adapted and optimized for severe marine and subsea conditions. In order to increase safety and minimize the danger from environmental loads present mostly at the sea surface, a major part of well installations and processing systems were moved subsea.
The environment found at the seabed is extremely aggressive. Very high pressures and processed corrosive chemicals, require the use of sophisticated design solutions and materials. Subsea installations are manufactured with the use of alloys of superb mechanical strength, resistance to corrosion and aggressive chemicals. These conditions are met by Duplex steel alloy, which is most commonly used in the Offshore Industry. Moreover, all subsea equipment has to be protected from corrosion with Cathodic Protection (CP). While being a very effective oxidization inhibition measure it has a major flaw – enhancement of Environmentally Assisted Corrosion (EAC).
Hydrogen Induced Stress Cracking (HISC), being a special case of EAC, is a common cause of equipment fatal integrity failure. A combination of high pressure, susceptible material and residual stresses caused by imperfections of manufacturing process can lead to cracking, which can pose a significant danger to the marine environment, human safety and project economy. All three requirements are commonly met at the subsea production systems. Although, the first two do not leave much space for optimization, the residual stresses found in the material are a scope with some room for improvement.
This study aims to find a relationship between the formation of residual stresses and welding process imperfections, being a primary cause of residual tension development within the material. Based on a Finite Element Method (FEM) transient simulation from a thermal perspective, the correlation between the welding parameters and heat distribution will be established and analyzed. The recent tendency to develop far north arctic areas (e.g., Goliath 2017, Snøhvit 2006, Johan Castberg 2022) were an inspiration to also focus on the influence of arctic conditions on welding process. The FEM simulation and Pearson Correlation will be used to analyze and compare the impact of extreme ambient temperatures on welding process. The results and conclusions should provide a solid foundation for welding process optimization in connection with Hydrogen Induced Stress Cracking. | |