The study involves Charpy V and CTOD testing and microstructure examination of a 50mm thick 0.05C–1.3Ni type S420 HSLA steel and associated weldments. The testing plates were welded using fabrication practice welding with normal welding equipment to simulate realistic working conditions. The plates were welded using two heat input conditions; 3.5 kJ/mm of submerged arc welding (SAW) for test panels A and B, and 1 kJ/mm of flux cored arc welding (FCAW) for panels C and D. Different welding consumables were applied for each test panel. The tests revealed excellent impact toughness properties of the base material with minimum values above 230 J down to −80°C. Moreover, acceptable results were obtained in the fusion line and weld metal for all panels tested at -40°C. At -60°C the Charpy values from the fusion line were all above 52 J and the CTOD values, except one for panel A, were above 0.2 mm. However, a significant scatter in properties was observed in the weld metal. In general, a marked drop in impact toughness was seen in the root compared to the CAP, which may be attributed to the welding consumables applied and the harsh weld configuration. Moreover, the highest CTOD properties were achieved from the two panels that were welded using the lowest heat input. The study has shown that acceptable properties of welded HSLA steels can be achieved at -60°C for certain weld combinations, even though the welding has been carried out under severe conditions. However, it was disclosed that future efforts should focus on improving weld metal toughness to enlarge the working range of steels for low temperature applications. Introduction Extraction of oil and gas resources in Arctic areas is characterized by extreme challenges from remote locations, poorly developed infrastructure, limited support systems, a highly sensitive environment and harsh weather conditions. Some of these challenges must be addressed through the application of robust materials, such as steels that are able to withstand low temperatures, large temperature variations and potentially large deformations from frost heave, ice and icebergs. Today there are commercially available high alloyed structural steels with very good low temperature properties. However, costs may prohibit large scale applications of such steels. Instead, high strength low alloy (HSLA) steels have been developed for wide range of oil and gas installations due to their beneficial mechanical properties, adequate weldability and low costs [1]. The steels receive their mechanical properties by the formation of a fine grained microstructure and favourable transformation products following thermo-mechanical controlled processing (TMCP) [2]. However, the operational properties of steels depend on the base material, the heat affected zone and the weld metal. For example, coarse grained regions and brittle phases may form in the heat affected zone during welding that can cause brittle failure. Therefore, it is important to restrict the formation of such regions and phases to obtain the target microstructure following welding.
The last decade Equinor has taken a significant amount of mooring chains out of service. Typically, one mooring line for an offshore installation has been replaced. Purpose has been to assess whether current chain condition (corrosion and wear), make the remaining chains fit for further use. The chains have been subject to thorough inspection, break load testing and fatigue testing. Depending on results of the inspection and tests, the remaining mooring chains have either been replaced or found fit for further use. From one installation, smaller cracks on the inside of the crown of chain links have been observed. These cracks do not coincide with known fatigue hot spots or fatigue breakages from fatigue testing of chains. Many cracks are visible with the bare eye, and NDT techniques are not necessary for detection. Chains with such cracks have been subject to both break load testing and fatigue testing. Overload breakage and fatigue cracks have not occurred or developed from the cracks. Chain links with cracks have been dissected to investigate crack depth. Dissection has also aimed to assess the age of the cracks. Both chain links that have and have not been subject to full scale fatigue testing have been dissected. This paper presents example of the observed cracks, including details on link location in the mooring line, crack positions in links, and measured depth and length of cracks. The paper also discusses the different possible causes of the cracks, and whether the cracks are critical for the endurance of the chains.
In the present investigation the aptness of the HYB process for butt welding of 4mm AA6082‐T6 profiles is evaluated and benchmarked against one gas metal arc (GMA) weld and one friction stir (FS) weld, representing best practice for both methods. The tensile testing shows that the yield strength of the HYB weld exceeds that of the GMA weld and is comparable with that of the FS weld. When it comes to impact toughness the HYB weld is the superior one of the three. Since the subsequent transverse bend testing did not reveal any evidence of bonding defects or crack formation, it means that the 4mm AA6082‐T6 HYB butt weld meets all acceptance criteria being specified by Equinor for offshore use.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.