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In the North Sea oil and gas installations, steel castings have been used for many decades. Here, high strength steel castings offer the chance to manufacture complex heavy-lift and fatigue-critical components for larger offshore structures without increasing the weight of the components or platforms. However, when the activities are moving north to colder climates, current existing castings may fail to meet the toughness requirements, and there is very limited information available on behaviour of weldments of castings under such extreme conditions. Therefore, the present investigation was carried out addressing the low temperature toughness of high nickel (~1.5% Ni) steel casting with 460 MPa yield strength. Preliminary welding trials were performed with flux-cored arc welding (FCAW) with an overmatch in weld metal strength. Both Charpy V notch impact and CTOD fracture mechanical testing were included at ?60°C. The results show that the Charpy V notch toughness is excellent at -60°C (> 100 J). The fusion line CTOD fracture toughness showed low values for the SENB05 samples, while SENB02 gave higher values. For both geometries, the lowest values were connected with pop-in events. The weld metal fracture toughness was satisfactory with the lowest value of 0.28 mm.
This paper presents early-stage results from a program to characterize the overall performance of flux core (FCAW) and submerged arc welding (SAW) consumables for arctic service and assesses a potential welding technique that may enhance the low temperature fracture toughness properties of welds for structural applications that will be used in arctic service where air temperatures can approach -600C. The results will be instrumental to engineers involved in material selection, weld procedure development and specification, and integrity specialists responsible for establishing fabrication and inspection criteria for arctic structures.
This paper presents results from a recently completed program that evaluated numerous commercially available flux-cored arc welding and submerged arc welding consumables designed for use with structural steels having nominal yield strengths of 70 to 80 ksi (483 to 552 MPa). The program characterized tensile and toughness properties of test welds as a function of welding process and parameters. The paper provides guidance on the optimum welding conditions that will help maintain minimum weld metal strength and toughness properties for high-strength steels used in critical offshore structures.
As the oil and gas industry continues to develop reservoirs in deep water, the growing complexity and desire for weight limitations in deep water installations is driving the need for use of higher-strength plate steel (>65 ksi (450 MPa) yield strength (YS)). Steel manufacturers are able to produce quality base materials with appropriate strength and toughness levels to meet the current need. However, structural fabricators that have traditionally built this type of infrastructure have not had much experience in working with steels in this strength level. These fabricators often work with materials not exceeding 50 or 60 ksi (345 or 414 MPa) in YS and some have, consequently, expressed concern about taking on fabrication projects requiring higher-strength materials.
The concerns fabricators have identified include:
Without adequate guidance offered to the industry, expanded use of high-strength steels (HSS) could be constrained due to these perceived technology gaps in welding of these materials. As a consequence, the design and weight saving advantages that HSS offers for deep water installations may not be fully realized without prudent guidance on optimized welding parameters.
To aid in addressing some of these issues, a program was funded by the Oil & Gas Strategic Technology Committee, coordinated by EWI, to characterize typical mechanical and metallurgical properties that can be achieved using commercially available submerged arc welding (SAW) and flux-cored arc welding (FCAW) consumables having nominal yield strengths of 70 and 80 ksi (483 and552 MPa). The results of this program will aid in establishing weld procedure specification requirements for HSS.
In evaluation of materials for arctic applications, their low temperature properties are addressed. The heat affected zone toughness has been shown to be critical with respect to satisfactory fracture toughness. Less attention has been given to the weld metal. Therefore, the present study was initiated with the objective to assess the fracture toughness of weld metals deposited with different welding wires. Both impact and fracture toughness testing were included; the latter one considered testing of full sized single edge notch bending specimens with through thickness notch in the weld metal and sub-sized specimens with surface notch in primary weld metal and in re-heated weld metal. The testing was performed at -60°C and three parallels were run for all configurations.
The results showed that both the Charpy V notch and fracture toughness varied substantially between the different welding wires employed. For the Charpy case, impact properties scattered from about 20 J for Weld 3 to 75-115 J for Weld 5. This ranking changed when it comes to full size CTOD specimens. Still Weld 3 had lowest values, while Welds 1 and 2 appeared with best toughness. The behaviour of Welds 1 and 2 was also different from the other welds regarding sub-sized samples with notches in the primary and reheated weld metals. Here, Welds 1 and 2 had similar toughness for the two weld metal regions, while Welds 3, 4 and 5 had higher CTOD values for the reheated weld metal. These results are discussed in terms of the weld metal microstructure observations.