On development of test equipment for strengh and leak tests of submersibles designed to probe extreme depths of World Ocean

Object and purpose of research. The object of study is an upgradation of the unique land-based pressure tank DK-600 of Krylov State Research Centre designed to test underwater technologies for strength and leak under external pressures from 90 to 100 MPа. The purpose is to support acceptance tests of pressure hulls and equipment for advanced manned autonomous submersibles of extreme diving depths to 11 500 m. In accordance with the world practices in development of deepwater submersibles it is required to achieve pressures of about 135–140 МPа. Materials and methods. С использованием современных численных методов Preliminary calculations of strength are performed using up-to-date numerical methods (FE analysis), the choice of structural material is validated as weldable steel forgings, strength category 750–800 МPа. Main results. The procedure and setup are suggested (Capsule DК-600) to provide the said tests by placing a special splittype intermediate Capsule capable to generate 135–140 МPа on the test object inside the pressure tank DК-600 with pressures of 85–90 МPа. The Capsule can accommodate a test object of up to 2400 mm (transverse dimension). Conclusion. Results of an exploratory design study are presented to upgrade the unique land-based pressure tank, which would put the KSRC hydrobaric tank at the world forefront in terms of proof pressures for testing the strength and reliability of extremely deep diving submersibles measuring within 2400 mm (transverse dimension).

New Weldable Steel for Rebars

A new steel grade, developed at the CELSA steelworks in Ostrowiec Świętokrzyski and used in the production of rebars, contributes greatly to the development of industrial and civil engineering. Steel B600B is characterised by yield point fyk = 600 MPa and immediate tensile strength ftk = 700 MPa. Tests revealed that the steel satisfies all requirements of related standards, both in terms of strength and processing properties. The mechanical properties of the new steel grade are higher by 20% than those of currently produced steels characterised by the highest mechanical properties (characteristic yield point Re= 500 MPa). As a result, the application of the new steel provides notable technical and economic advantages. The new steel grade meets requirements concerning technical class C in accordance with PN-EN 1992-1-1, which indicates that the steel has a significant yield point margin (being an important advantage in terms of limit state design). Plastic steels are easier to weld and less susceptible to welding crack formation. Technological (research-related) tests revealed the favourable welding properties of the new steel. Welding tests were performed using the manual metal arc welding method, i.e. the most common welding process used when making structural reinforcements. The welding tests involved the making of butt, overlap and cruciform joints. The strength and technological tests revealed that the steel satisfied the requirements specified in the PN-EN ISO 17660-1 standard.

The Weldability of Duplex Stainless-Steel in Structural Components to Withstand Corrosive Marine Environments

There is still a considerable gap in the definition of the weldability of Duplex Stainless Steel (DSS). A lack of clarity that is explained by the standard specification of the maximum content of equivalent carbon that defines a “weldable” steel coupled with the fact that the alloying elements of DSS exceed this defined limit of weldability. In this paper, welding quality in an inert environment and in presence of chlorides is analyzed with the aim of defining optimum welding conditions of 2001, 2304, and 2205 DSS. The same procedure is followed for a hybrid weld between DSS 2205 and a low carbon mild steel, S275JR. As main output, this study defined the optimal welding conditions with tungsten inert gas without filler for each type of DSS weld that showed excellent anti-corrosion performance, with the exception of the DSS 2205-S275JR weld where widespread corrosion was observed. Additionally, this study established a relationship between the thermal input during welding and the content of alloying elements in defect-free joints. Furthermore, it demonstrated that an increase in ferrite content did not lead to a worse corrosion resistance, as expected after passivation.

Quality Assessment of Weldable Steel Mark P355NH from Decompression Chamber Construction for Diving

Non-alloyed P355NH steel according to EN 10028-3:2003 belongs to a group of fine-grained steels for pressure vessels being used in welded construction at decompression chamber for divers. Values of the chemical, structural and mechanical characteristics and steel toughness experimentally determined fit the analyzed steel in P355NH steel group according to EN 10028-3:2003. The toughness of the analyzed steel at the test temperature of -30°C is characterized by high values of fracture energy KV in longitudinal direction between 48 and 86 J and on transverse direction between 17 and 34J. Steel toughness at the test temperature of -30°C required by ABS standard (in Section 4/5.3 and Table 1) provides for breaking energy KV of min. 35J, with ductile fracture surfaces, value that is not respected at some lots of the three batches (A, B, C) of steel. Finally, based on the direct correlation established between HV10 hardness of the fine structure and the toughness it was made a selection of the lots of non-alloy steel P355NH which correspond to ABS norm for welded construction of the decompression chamber for divers