Large-diameter Steel Tube Research Articles

Experimental and numerical investigation on the deformation behaviors of large diameter steel tubes under concentrated lateral impact loads

Large diameter steel tubes are widely used in bottom fixed and floating offshore wind turbines. Offshore wind turbines (OWTs) operating in the oceans are exposed to the risk of collisions when ships pass and dock at turbines. Thus, it is extremely important to investigate the impact mechanics of ship-OWT collisions and propose practical designs for methods to protect OWTs from collision loads. This paper presents a series of experimental and numerical studies on the deformation behaviors of large diameter steel tubes from a NREL 5 MW spar-type floating offshore wind turbine (FOWT) under lateral impact loads. These studies consider the effects of different impact velocities, attached masses, diameters and thicknesses of the tubes on their response to impact loading. In these experiments, a rigid indenter was mounted on a pendulum system and accelerated to strike the tubes; the scale was 1:30. The dimensions of the indenter head were much smaller than the tube diameter in order to concentrate the impact load. Global motions of the impacted tubes were modeled by springs introduced at the boundaries, and their stiffnesses were determined according to an equivalent single-degree-of-freedom (SDOF) model. Numerical simulations of the experiments were conducted using the nonlinear finite element (FE) software LS-DYNA. The experimental and numerical results were compared and discussed with respect to force-deformation curves, deformation modes and energy dissipation. Existing theoretical solutions for the lateral indentation resistance of tubes were also compared to the experimental and numerical simulation data. The results indicated needs for new solutions when the impact loads become concentrated.

Rapid online analysis of trace elements in steel using a mobile fiber-optic laser-induced breakdown spectroscopy system

A mobile fiber-optic laser-induced breakdown spectrometer (FO-LIBS) prototype was developed to rapidly detect a large quantity of steel material online and quantitatively analyze the trace elements in a large-diameter steel tube. Twenty-four standard samples and a polynomial fitting method were used to establish calibration curve models. The R2 factors of the calibration curves were all above 0.99, except for Cu, indicating the elements’ strong self-absorption effect. Five special steel materials were rapidly detected in the steel mill. The average absolute errors of Mn, Cr, Ni, V, Cu, and Mo in the special steel materials were 0.039, 0.440, 0.033, 0.057, 0.003, and 0.07 wt%, respectively, and their average relative errors fluctuated from 2.9% to 15.7%. The results demonstrated that the performance of this mobile FO-LIBS prototype can be compared with that of most conventional LIBS systems, but the more robust and flexible characteristics of the FO-LIBS prototype provide a feasible approach for promoting LIBS from the laboratory to the industry.

Failure analysis of a Cu 12Mn mechanical fastener in marine environment

Abstract The current work presents a failure analysis study conducted on a fractured mechanical fastener made of Cu 12Mn alloy. The fastener was obtained from a flange of a large-diameter steel tube operating in a sea submersible platform. Macrofractography and Microfractography, Standard Optical Metallography, Scanning Electron Microscopy (SEM), X-ray Fluorescence (XRF) and Energy-Dispersive X-ray Spectroscopy techniques as well as Numerical Modeling were employed to assist the investigation. Fracture was eventually attributed to the synergistic action of fatigue and selective leaching (corrosion-assisted fatigue).

Forming limit in burring process of large diameter steel tube

Forming limit in burring process of large diameter steel tube

FEM Analysis and Forming Limit in Burring Process of Large Diameter Steel Tube

FEM Analysis and Forming Limit in Burring Process of Large Diameter Steel Tube

Fatigue Strength of Brace Connections in Semi-Submersible Rig

Among various offshore structures, semi-submersible rigs constructed of large diameter steel tubes have been given various types of reinforcement at their brace connections to insure their fatigue strength, which is one of the important problems directly related with the integrity of such structuresThe rapid growth in development of marine resources has led to severer design conditions of a semi-submersible rig to be built for operation in deeper waters subject to higher waves and polar atmosphere. On the other hand, the pursuit of economy in the development is also an essential problem. This paper presents, as an approach to the above problems, a fatigue strength assessment method obtained through the development of a highly fatigue-resistant connection with considerations given to some problems involved therein.For higher fatigue strength, one of the measures to be taken is to reduce stress concentration. With the new connection, it was possible to limit the stress concentration factor below 2 for welds at bracket toes, intersections, etc. From this fact, the fatigue life will be expected to sufficiently exceed the endurance period of 20 years.Unexpectedly great influence on fatigue strength has been observed depending on the determination method of the stress frequency pattern and the wave direction, which are considered to be thoroughly clarified for future improvement of the design accuracy.

All-Weather Tanker Terminal For Cook Inlet, Alaska

This paper describes the design and construction of a 30,000 DWT to 60,000 DWT capacity tanker loading facility constructed in Cook Inlet, Alaska for year-round operations. Particular emphasis is placed on the environmental conditions and resulting design criteria which led to the conception of the unique structure. Large diameter steel tubes, supported by underwater bracing, were used as the main structural members which extended through the ice zone. A movable fender system was designed to remain a few feet above the water level and thus provide a uniform fendering capability at all tidal levels without exposure to ice damage. The dock components were prefabricated in large units to reduce on-site work to a minimum.

The Aero and Motor Exhibition

THIS exhibition opened at Olympia on Friday, March 24, and will continue until Saturday, April 1. A general survey of the flying machines shown indicates that the crank inventor is less conspicuous than has been the case at former exhibitions, and that the British makers have achieved notable progress during the past twelve months both as regards design and workmanship. Most of the machines have evidently been designed and con structed with a view to military requirements. Thus among foreign machines is the Breguet three-section military biplane, one of the favourites with the French War Department. This machine is built almost entirely of steel, thus cutting down the number of parts and the amount of wiring. The spars of the wings consist of large diameter steel tubes, to which the ribs are elastically attached, forming a supple surface which is claimed to give almost entire automatic stability. Another French War Department machine is the Nieuport two-seater monoplane, chiefly remarkable for its high speed—63 miles per hour.