Abstract
This work aims to compare the ultrasonic inspection of 9%Ni steel joints welded with the Gas Metal Arc Welding (GMAW) process and Shielded Metal Arc Welding (SMAW) process. These are the two most widely used processes used to weld pipes for CO2 injection units for floating production storage and offloading (FPSO) in the Brazilian oil and gas industry. The SMAW equipment is simple and portable, which is convenient for the FPSO; however, the GMAW process has the advantage of welding with high productivity. In this study we performed a numerical simulation using the software CIVA, 11th version, to analyze the behavior of ultrasonic longitudinal wave beams through GMAW and SMAW dissimilar weld joints. Ultrasonic tests were performed on calibration blocks drawn from both welded joints to evaluate the simulation results. The results are discussed with regard to the microstructure of the weld metal via electron backscatter diffraction (EBSD) analyses. The SMAW process presented better inspection performance than the GMAW process in terms of attenuation and dispersion effects. Although the SMAW had a better outcome, for both processes the configuration of 16 active elements and a scanning angle of 48° resulted in an optimized inspection of the entire joint.
Highlights
Since 2010, 9%Ni steel has been used in CO2 injection units in Brazil’s pre-salt oil and gas reservoirs.This application is new worldwide and requires massive, thick-walled pipes because of the high working pressure in the floating production storage and offloading (FPSO) CO2 injection unit
A marked difference in attenuation level was perceived between the two weld metals and the base metal (Table 6)
Comparing Figure 7a2 to Figure 7b2, it is possible to observe that the noise level after the second echo was much higher for the Gas Metal Arc Welding (GMAW) weld metal
Summary
Since 2010, 9%Ni steel has been used in CO2 injection units in Brazil’s pre-salt oil and gas reservoirs.This application is new worldwide and requires massive, thick-walled pipes because of the high working pressure in the floating production storage and offloading (FPSO) CO2 injection unit (around550 bar/55 MPa). According to Tenge and his coworkers [1], lack of sidewall fusion is the defect type that constitutes the highest degree of severity found in 9%Ni steel joints welded with Ni-based superalloy as a filler metal due to higher sensitivity to variations in welding conditions, including the groove setup. This defect is more frequent in GMAW weldments. This region is adjacent to the heat-affected zone (HAZ), where the fracture toughness is usually less than that of the base metal, and there is a concentration of residual stresses produced by the thermal welding cycles
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