A Study on Unification of Welding Consumables in Construction of Chemical Cargo Tanker Made of Duplex Stainless Steel: Evaluation of Static Strength of Welded Joint

Austenitic stainless steels such as SUS 316 LN and austenitic stainless clad steel are used in cargo holds of chemical tankers owing to their corrosion resistance. Recently, the use of duplex stainless steels has been increasing, owing to their better strength and corrosion resistance and lower content of expensive Ni, compared with those features of austenitic stainless steels. However, few duplex stainless clad steels have been approved by classification bodies. Furthermore, the application of duplex stainless steel is not yet mainstream as hull structural materials because a stable supply market has yet to be established. Therefore, when applying cladding steel to construction of chemical tankers, austenitic stainless clad steel is often used at present. The duplex stainless steel and the austenitic stainless clad steel are mixed at construction factories; hence, there is a risk of misuse of welding consumables. If misuse is suspected, it is not possible to judge the erroneous use from visual inspection after construction; therefore it is necessary to uniformly remove the weld and re-weld. However, if universal welding consumables were identified, this might avoid the problems of misuse and simplify the procurement of welding materials. In this paper, we report on our studies to verify welding consumables for use in the hull structures, involving a mixture of duplex stainless steel and the austenitic stainless clad steel. The static strength of the welded joints is a particular focus of this study, from which we confirmed the validity and limitations of welding consumables.

Numerical Analysis of Hydrogen Distribution in Welds of Stainless Clad Steels for Hydrogen Storage Pressure Vessels

Numerical analysis of hydrogen distributions in the welds of stainless clad steels, which are the structural material of hydrogen storage pressure vessels, was conducted to predict the hydrogen embrittlement in the pressure vessels. The theoretical model for the calculation was based on the activity of hydrogen considering residual stresses induced by welding and hydrogen accumulating sites such as precipitates and dislocations. From the calculations, hydrogen concentrates at the center of weld metals in both of longitudinal and circumferential directions in welded joints of stainless clad steels. However, the hydrogen contents were much lower than those in the carbide layers, in which are observed in steels with weld overlay of stainless steels, as the calculation of hydrogen distribution in the materials using the higher evaluated diffusion coefficient of hydrogen with considering margin of safety. Therefore, it seemed that the risk of cold cracking due to hydrogen embrittlement was sufficiently lower in the welds of stainless clad steels during many cycles of shutdown and restart of the pressure vessels in long-term operation.

Progress of Laminated Materials and Clad Steels Production

Laminated materials and clad metals have received much attention in the industrial production due to the superior mechanical properties different from those in any of the constituent materials. Clad metal is a composite metal plate generally made by bonding a metal such as stainless steel plate to another metal such as carbon steel or low alloy steel plate. Clad metal not only has sufficient strength required of structural materials but provides other functions including resistance to heat and corrosion. As a result, the application of clad metals can significantly save precious alloying elements and reduce the cost. Therefore, clad metals have become an increasingly interesting topic in a variety of industrial fields. In this paper, fabrication technique and evaluation on mechanical properties of laminated metals have been briefly overviewed. In addition, the applications of laminated materials including clad metals are reviewed and the prospect of clad metals in the future is also described.