5xxx series aluminum alloys find increasing applications in the marine fabrication industries due to its unique mechanical and corrosion properties. The present attempt focuses the effect of metallurgical changes in mechanical behavior and corrosion resistance of Aluminium alloy 5083-H111 and its weldment. Gas tungsten arc welding (GTAW) process was used to fabricate the weld coupons using the filler metal ER 5183. Microstructure analysis was carried out in the fusion zone and compared to the heat affected zone and parent metal region. The mechanical behavior of the weld was compared with its parent metal by performing microhardness, impact toughness, tensile behavior and formability test. Electrochemical corrosion test revealed better corrosion resistance for parent metal sample than the weldment. The existence of Mg3Al2 precipitates in the weldment led to the reduction in corrosion resistance

The present investigation aims to analyze the anisotropy behavior of 8mm thick rolled plate of duplex stainless steel AISI 2205. The study aims to connect the importance of anisotropy properties with fusion welding to achieve the optimal mechanical properties of the weldment by justifying suitable direction for welding. An outcome of the investigation implies that duplex stainless steel exhibits maximum impact toughness in the longitudinal direction i.e. rolling direction when compared to transverse and diagonal directions. Further, the existence of significant directionality was confirmed by analyzing the tensile behavior which gives greater tensile strength in the transverse direction and higher amount of elongation and better formability in the longitudinal direction. The present work was extended by fabricating the weldment using gas tungsten arc welding by keeping the welding direction perpendicular to the rolling direction of a plate. Microstructure and the mechanical properties of the weld were assessed and compared with the behavior of its parent metal.

In the present review, attempts have been made to analyze the metallurgical, mechanical, and corrosion properties of commercial marine alloy duplex stainless steel AISI 2205 with special reference to its weldability, machinability, and surfacing. In the first part, effects of various fusion and solid-state welding processes on joining DSS 2205 with similar and dissimilar metals are addressed. Microstructural changes during the weld cooling cycle such as austenite reformation, partitioning of alloying elements, HAZ transformations, and the intermetallic precipitations are analyzed and compared with the different welding techniques. In the second part, machinability of DSS 2205 is compared with the commercial ASS grades in order to justify the quality of machining. In the third part, the importance of surface quality in a marine exposure is emphasized and the enhancement of surface properties through peening techniques is highlighted. The research gaps and inferences highlighted in this review will be more useful for the fabrications involved in the marine applications.

The present work is an effort to study the influence of shot peening on the exfoliation corrosion behavior of aluminium alloy (AA) 5083. Surface textural changes induced by shot peening was characterized using microstructural and X-ray diffraction analysis. The surface roughness parameters were measured to study the benefits of peening induced surface topography. Further, the hardness survey was carried out to assess the severe plastic deformation on the peened layers. As a result, excellent resistance against exfoliation corrosion was achieved in the chloride environment. Shot peening plays major role in enhancing the corrosion resistance of AA 5083. In the absence of exfoliation attack, the unpeened sample surfaces such as ground, milled, and as received conditions end up with a significant pitting attack. The findings of this work will be useful for the aluminium alloy fabrications involved in the marine applications.

In the present investigation, an attempt has been made to enhance the surface quality of austenitic stainless steel 316L and duplex stainless steel 2205 through shot peening process. The study mainly focuses the surface morphology, microstructural changes, surface roughness and microhardness of the peened layers. Metallography analysis was carried out and compared with the unpeened surface characteristics. As result of peening process, surface recrystallization was achieved on the layers of the peened samples. It was found that shot peening plays significant role in enhancing the surface properties of 316L and 2205. Particularly it has greater influence on the work hardening of austenitic stainless steel than the duplex stainless steel due to its more ductility nature under the investigated shot peening parameters. The findings of the present study will be useful with regard to the enhancement of surface texture achieved through peening.

In this investigation, analysis of surface topography on Duplex Stainless Steel (DSS) AISI 2205 was carried out under the shot peened and various machined conditions. The surface profiles of the shot peened, polished, milled, ground and as received conditions were compared in micron level. In order to study the influence of shot peening on the profile of surface roughness, DSS samples were peened using S390 shots for different durations. Severe Plastic Deformation (SPD) was observed on the surface of DSS due to peening. Also, peening has more effect on the austenite phases than the ferrite phases on DSS surface. The shot peened surface profiles obtained using S390 shots offer better topography as compared with the other machined and as received surface conditions. As a part of the study, the effect of dual shot peening was inspected by peening the surface using two shots which introduce lots of micro peaks and valleys on the surface of DSS.

The optimum design of an integrated mining system for polymetallic nodule mining is mainly dictated by the soil properties of extremely soft seabed at depths of 5000-6000 m. During the design process, the entire weight distribution and traction of the mining machine has to be configured by considering the bearing strength and shear strength parameters of the soil. The shear strength of the soil also provides useful information on the maneuverability and control of the mining machine. It is also imperative that the mining area be delineated to eliminate vulnerable areas of low strength where the equipment may sink suddenly beyond recovery due to anchoring of the machine. A remotely operable in-situ soil tester has been developed for 6000-m operations, with a cone tester and a shear vane tester for soft soils and shallow depth of penetration. This paper describes the methodology used for soil property measurements and the soil tester's performance at 5462-m water depth in the Central Indian Ocean Basin.

Deep seabed polymetallic nodule mining machines have to operate in extremely soft ocean floor having soils of shear strength in the order of 1-3 kPa. The extent of sinkage and pullout force or breakout force required to lift the mining machine from the seafloor bottom needs to be evaluated for the successful operation and retrieval of the mining machine. In most of the cases the breakout force exceeds the submerged weight of object. Most of the empirical equations for estimating breakout forces are based on the bearing capacity phenomena. In the present study experimental investigations have been carried for obtaining undrained or immediate breakout forces on flat plates, plates with involute grousers and single track unit of Undercarriage unit. The magnitude of forces so obtained from the experiments has been compared to those calculated from the empirical equations. Studies on the extent of sinkage in soft sediments is critical for quantification of resistances encountered by the mining machine which influences the maneuverability of the mining machine. Experimental investigations have been carried out on flat plates, flat plates with grousers and single track of undercarriage unit as a part of sinkage studies. Sinkage has also been studied by Finite Element Methods using MohrCoulomb material model neglecting angle of internal friction angle as soils were fully cohesive and solving through explicit methods.

The speed and heading control of the deep sea tracked mining machine is one of the significant aspect for maneuvering of the underwater crawler based mining machine in various terrains and carry out the turning movement on the deep sea soil. In this paper, a mathematical model is used to simulate the dynamics of the mining machine considering all the internal and external resistances acting on the machine. A co-simulation of mathematical model with a virtual model of the underwater mining machine has been used to control the mining machine for heading control for the locomotion of the mining machine in deep sea soil conditions.

An underwater mining system has been developed for mining polymetallic modules and qualified in shallow water at 512m depth. The mining system has a remotely operable underwater mining machine which collects seabed nodules, crushes and pumps the same through a flexible riser to the mother ship. The machine is equipped with Acoustic Positioning system, Altimeter, Doppler Velocity Log (DVL), Proximity sensors, Linear Variable Differential Transformer (LVDT), Pressure, Temperature, Motion Reference Unit (MRU), Underwater Camera and lamps for various measurement and operation of underwater mining machine. The machine was tested at Angira Bank off Malvan coast during Oct 2010. This paper presents the details of performance of various underwater sensors, Telemetry & Data Acquisition system at 512m depth. Based on the results from the tests, the next phase of 6000m operations is being attempted.

Load cells are the devices which can be used for different types of weighing applications. This paper presents the design of a pressure compensated strain gauge based load cell which can be operated for various deep sea applications. This load cell is a transducer that is used to convert a force or load into electrical signal. This conversion is indirect and happens in two stages. Through a mechanical arrangement, the force is sensed which deforms the strain gauge and the deformation (strain) is measured as an electrical signal, because the strain changes the effective electrical resistance of the wire. This load cell is designed with full Wheatstone bridge configuration for detecting both tension and compression load and also for ensuring better accuracy. The electrical signal output is typically of the order of a few mill volts and needs conditioning with necessary signal processing circuitry before it can be used further. Finally the device needs to be enclosed inside a pressure compensated enclosure which can withstand 600 bar outside pressure. The device is mainly designed considering the Indian Ocean parameters and it will work at a depth of 6000 meters under water.

An under-water mining system using flexible riser concept was demonstrated for operations in the Indian seas at 410 metres water depth in 2000 for short duration. Based on the tests, enhancements were done on the mining system for long term operations in areas pertaining to distribution of buoyancy packs, sealing and heat dissipation arrangements. The mother ship was also equipped with Launch and Recovery System and Dynamic Positioning System. The modified system was tested for long term maneuverability and pumping operations at 451 in depth in 2006. The paper discusses the enhancements carried on the mining system and the mother vessel and the results from the sea tests.

As underwater mining machine were relied upon to perform complex operations offshore, in ever increasing water depths, positioning and control of the machine is one of the major issue where it becomes the limiting factor in the performance of the entire system. The control and data acquisition of the mining system must be flexible and capable of being configured for multi tasks with in short time and perform the operations as programmed in real-time basis. This was achieved by designing the data acquisition and control system of the mining machine based on virtual instrumentation concept using compact field point modules from National Instruments, which is an embedded real-time programmable automation controller that runs Lab VIEWTM Real-Time, providing the functionality, connectivity, and flexibility on a small rugged, industrial platform. Acoustic positioning system for the underwater mining machine was based on Super Short Base Line (SSBL) principle which was achieved by having one vessel-mounted transducer with the range of 4000 m and two Sub Sea transponders mounted in the machine. The positioning system provides online position status of the crawler in X, Y and Z directions with reference to the mother vessel. With the help of the acoustic positioning system and its GUI based software, it was possible to track the position of the machine in real time with reference to mother vessel during the sea test. Apart from online position tracking of the mining machine the data were recorded for post analysis. The mother vessel was equipped with Dynamic positioning system and Launching and recovery system to ease the positioning, deployment and retrieval operations of the deep sea crawling machine. The objective of the paper is to present in detail the data acquisition, control and positioning system of the underwater mining machine along with the sea test results.

An underwater mining system with a crawler based mining machine and a flexible riser system has been conceptualised for manganese nodule mining. The flexible riser system with a single positive displacement pump mounted on the mining machine is different from the rigid riser concepts of the seventies where multiple pumps are mounted at different levels along the riser. The system has been tested for mining operations at 410 metres water depth. Four tests were carried out on this system in the Indian seas. The paper discusses the flexible riser concept, details of the tests carried out and results obtained. Specific details of pumping and maneuverability tests carried out are discussed. Based on results from the tests enhancements proposed for future deep sea mining systems are also discussed.

The functions of the crawler for mining and driving are all remotely controlled from the control computers on the ship. Various sensors allow comprehensive monitoring of the perfonnance of the crawler. The crawler computer is based on Pc/I04 modules in connection with a standard industrial field bus system (Interbus) for data acquisition and control. The software used in the sand mining system consists of the process visualisation software in the control room, the control software for development and implementation of the main control program, and the operating systems of the crawler computer and the control computers.

Underwater sand mining system consisting of a crawler that can mine and pump sand slurry from 500 metre water depth through a flexible hose to the mother ship has been designed and developed as the first step towards development of technology for deep sea mining. The crawler rs designed to work on a soft sea bed and has a special track belt with involute teeth to compact the bed during motion. The crawler has a manipulator arm with a cutter to sweep the seabed and mine sand and a positive displacement pump to deliver the sand slurry to the mother ship through a flexible hose. A cone tester and vane tester are provided to perform soil testing in-situ. The main drives of the crawler are hydraulically operated. The crawler has transducers for measurement of velocity, drum speed, heading, sand concentration etc. and has a closed loop control for speed, heading and slip. An umbilical cable with an outer steel armour carries the weight of the crawler during launching and retrieval. The cable has copper conductors and optical fibres for power and data transmission respectively. The crawler has been designed for a pressure rating of 600 bar. The system has been tested for locomotion, pumping etc. on land and was soak tested in the sea and water pumped using the slurry pump.

An underwater mining system which is a crawler based system consisting of a mining machine moving on the sea bed collecting polymetallic nodules, crushing and pumping the crushed nodules through a flexible riser to the mother ship by a slurry pump has been developed. The slurry pump is a single stage positive displacement type driven by an independent hydraulic system that pumps nodules. Pressure drop studies for clear water and slurry flow with solids through flexible hoses of varied bend angles and various bend radii were conducted using the solids pump in an experimental test setup. The studies were conducted for the most likely occurring bend angle of 70, 20 and 60 with a bend radius of 5 times the hose diameter for various flow rates. The results of 20 bend angle were compared with the steady state pressure drop values obtained using Computational Fluid Dynamics using FLUENT software. The results from the tests were useful in conducting subsea tests on underwater mining machine at 1032 m depth.