Characterization of Hydrogen Diffusion in Offshore Steel S420G2+M Multi-layer Submerged Arc Welded Joint

Abstract

As onshore installation capacity is limited, the increase in the number of offshore wind turbines (OWT) is a major goal. In that connection, the OWTs continuously increase in size and weight and demand adequate foundations concepts like monopiles or tripods. These components are typically manufactured from welded mild steel plates with thickness up to 200 mm. The predominant welding technique is submerged arc welding (SAW). In accordance with the standards, the occurrence of hydrogen-assisted cracking is anticipated by either a minimum waiting time (MWT, before non-destructive testing of the welded joint is allowed) at ambient or a hydrogen removal heat treatment (HRHT) at elevated temperatures. The effectiveness of both can be estimated by calculation of the diffusion time, i.e., diffusion coefficients. In this study, these coefficients are obtained for the first time for a thick-walled S420G2+M offshore steel grade and its multi-layer SAW joint. The electrochemical permeation technique at ambient temperature is used for the determination of diffusion coefficients for both the base material and the weld metal. The coefficients are within a range of 10−5 to 10−4 mm2/s (whereas the weld metal had the lowest) and are used for an analytical and numerical calculation of the hydrogen diffusion and the related MWT. The results showed that long MWT can occur, which would be necessary to significantly decrease the hydrogen concentration. Weld metal diffusion coefficients at elevated temperatures were calculated from hydrogen desorption experiments by carrier gas hot extraction. They are within a range of 10−3 mm2/s and used for the characterization of a HRHT dwell-time. The analytical calculation shows the same tendency of long necessary times also at elevated temperatures. That means the necessary time is strongly influenced by the considered plate thickness and the estimation of any MWT/HRHT via diffusion coefficients should be critically discussed.

Effect of Arc Strikes on High Strength Low Alloy Steels Welded by SMAW

“…The state of the art regarding arc strikes includes the regulations of classification societies and a few scientific articles. According to the DN-VGL-OS-C401 guidelines [30]: "arc strikes shall be repaired by mechanical removal of affected base material followed by Magnetic Particle Testing (MT) in order to verify absence of cracks". Removal of arc strikes usually requires a grinding process.…”

Cause Analysis of Low Tensile Plasticity in Normal Direction for Hot‐Rolled Thick Plate of HSLA Steel

“…As the temperature of the thick plate decreased, the supersaturated hydrogen in steel would be released and normally entered the atmosphere by diffusion. [18][19][20] In the case of thick or extra-thick plate, the hydrogen in the center did not easily diffuse to the atmosphere so that led to internal defects such as white spots and hydrogen-induced cracks. Such defects could reduce the tensile plasticity in ND of the thick plate.…”