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Developing the largest size dredge pump in dredging industry

As the demand for larger dredgers rises, there is a growing need for developing largest size dredge pump that can reach up to 1,800 mm suction diameter.

The largest size dredge pump is one of the main components of the dredger, and it is critical to achieving production. Dredge pumps also have the biggest power consumer during operation so efforts to reduce the pump’s power needs through smarter design are critical.

Engineering challenges of dredge pumps

Dredge pumps involve more complex engineering challenge than water pumps. They must carry water filled with mixture of several types of soils like mud, fine sand, coarse sand, gravel, stones, and other debris. The mixture of those materials with pumped water doesn’t behave as homogenous fluid as the soil tends to settle down and slide on the pipe bed depending on the flow speed. Another challenge is that pump parts wear quickly. Clogged impellers and breaking vanes also pose risks to pump performance.

Dredge Yard’s largest size dredge pump design

In 2011, Dredge Yard began developing a new range of dredge pumps ranging from 200mm to 1,400mm – the largest size dredge pumps in the dredging industry. These pumps are designed to counter wear problems inherent in dredge pumps. Impellers are designed in multiple categories of 3, 4 and 5 vanes. To resist wear, the pump parts are made from high chromium iron having a hardness of 60HRC. Unfortunately these materials don’t have high elongation properties and are not impact resistant. For this reason, some dredge pumps are built with an outer casing.

The large pumps are connected in series, reaching a final pressure of 30 bar by the 3rd pump. The pumps often weight more than 100 tons for one complete assembly including wet parts, outer casing, plates, shaft, bearing assembly and pedestal.

Size, weight and component resistance, among other factors, create an imposing challenge for dredge pump designers. Demand has recently grown in the market for even bigger dredgers. Dredge pump size must increase from 1,400 mm to 1,600 mm – even 1,800 mm. Larger suction pipes and dredge pumps must be designed to fill the dredgers in less than 2 hours.

New design methods are needed to adapt to the market efficiently. Pumps must be tested and analyzed for their efficiency and performance. Foundries with casting capacity of 50 tons and heavy steel machinery 6 meters in diameter are required when casting and machining the pump case.

Performance analysis of the largest size dredge pump

The size of these dredger pumps makes building a test and analysis laboratory extremely difficult if not impossible. The manufacturer must design and manufacture the pump as a prototype and deliver the prototype to the dredger without testing and performance checks. All performance will be tested in the dredger when it starts working. The design has to be flawless, performance oriented and reliable before its production. Engineers at Dredge Yard test dredge pump performance with computational fluid dynamics (CFD) instead of physical testing. CFD software calculates and simulates the pump performance measurements like flow rate, aeration, cavitation, pumping head, efficiency, power required, and net positive suction head (NPSH).

CFD codes, can provide steady-state simulation, also known as multi-frame reference (MRF) simulation or “frozen blade” simulation, which put the impeller in a reference frame that rotates at the pump speed, while solving for the rest of the pump in the stationary lab frame.

3-D modeling

After achieving the hydraulic design, a basic 3-D pump model is made in several CAD programs. Once the basic design is completed Dredge Yard runs several trials on major FEA calculations on the model to ensure getting the right stiffness and strength of the pump. This model incorporates pressures output from the CFD analysis to determine the wall loadings.

The gap between the impeller and front plate must be tightly controlled in terms of geometric tolerance. If deformation widens the gap, efficiency will drop significantly. The 3-D modeling and FEA process is repeated as needed to ensure the highest safety margin and lowest weight. At 1,800 mm a dredge pump weights approximately 200 tons. Any weight savings from the FEA calculation could be significant.

Design work continues on the 1,800 mm dredge pump. Dredge Yard aims to finalize the development in 2016 and build the pumps for the dredging and mining market.

One of the examples of a geometric tolerance that needs to be tightly controlled is the gap between the impeller and the front plate. If there is a deformation in that area and the gap widens, the efficiency will drop significantly. Besides the impeller gap effect, the stiffening of the pump structure will assure a symmetrical tension on the pump case and plates. As the pump case is of a volute shape and pressure is not evenly spread, deformation could be asymmetric which is not desirable in pump structures.

The 3-D models takes into account such performance measurements as flow rate, head and cavitation for many of the pump’s components.

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Dredge Yard delivered turning glands for several TSHD’s

Dredge Turning Glands

The dredge turning glands will be used on board of several TSHD and they are designed according to the customer’s requirements and applications using the latest 3D CAD technologies and Finite Element Analysis to ensure achieving an optimum strength and stiffness.

Manufacturing

The turning glands are manufactured from cast carbon steel and fabricated steel and machined and assembled with Dredge Yard partners and Dredge Yard facility in the United Arab Emirates.

The inner pipe of the turning gland is made out of one casting to make the complete design stronger and stiffer while saving weight and material. Dredge Yard quality control inspectors scrutinize all the dredge turning glands during and after their production stages carrying out various tests such as the chemical composition and mechanical properties test, measurement test of all dimensions after casting and machining, ultra sonic testing, magnetic particle, surface roughness test and dye penetrant inspection for critical parts, measurement test of all dimensions after machining, hardness test, assembly and interchange ability test, visual inspection for all parts during and after assembly.

Latest component

The Dredge Turning Gland is the latest dredge component accurately and professionally developed by Dredge Yard team of engineers and it has several interconnected benefits making it a reliable product like a compact seal design making the assembly less heavy, adjustable turning range by using dismountable stoppers, and a heavy duty wall and flange thickness.

Dredge Yard’s official web site, www.dredgeyard.com, can provide further information relative to dredge turning gland and about all the dredging equipment and technology.

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Dredge suction mouth developed by Dredge Yard

Dredge suction mouth

Dredge Yard, a specialized company in dredging technology and dredging equipment based in the Netherlands and United Arab Emirates has announced the launch of the dredge suction mouth. The dredge suction mouth is a dredge component positioned behind the cutter head of a Cutter Suction dredger during extraction of non-cohesive material from the sea bed.

CAD & FEA

Dredge Yard team of engineers designed the dredge suction mouth using the latest 3D CAD technologies, latest production methods and they entirely scrutinized the designs using Finite Element Analysis. External and internal forces are examined and all maximum possible scenarios are simulated.

Production and design

In order to provide the most reliable dredge equipment with high accuracy and precise dimensions to fit in the cutter head and the suction pipe, Dredge Yard is using only one cast piece for the production of the dredge suction mouth that eliminates many operations, such as machining, forging and welding. Casting the suction mouth in one piece allows producing the most intricate shapes, both external and internal that can follow the shape of the flow. In this way competitive prices and shorter delivery times can be achieved.

The dredge suction mouths as well as the other components are designed, produced and tested under strict ISO and ASTM standards and double tested at third party for verification.

Materials

The following materials are being used according to the customer’s requirements: Carbon Steel that allows easy welding and hard facing if required; Carbon Manganese Steel that increases depth of hardening and improving the strength and toughness; and Alloy Steel in order to obtain higher performance in wear resistance.

Inspection

Dredge Yard performs numerous testing that occur during and after production process of the dredge suction mouth. Before making the pattern, casting simulation software is run to verify that all thickness, curves and radii will be obtained and the material will cool down in a good way preventing internal and external shrinkage. For all casting the mechanical and chemical properties are verified at the third party. A final inspection is performed by the Dredge Yard team of quality control in order to assure that the product is according to customer’s and Dredge Yard’s specifications.

After inspection, the cast surfaces are painted while the machined surfaced are greased. Dredge Yard team supervises the packing and transport to ensure the release of products in the right way.

Sizes of dredge suction mouth vary according to the customer’s dredgers, dredge cutter heads and dredge pipe arrangements.

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Extending the lifetime with Finite Element Analysis

FEA

Dredge Yard’s dredge components and equipment are designed using Finite Element Analysis in order to optimize the design and ensure low stress forces in the material. In this way the life time of the equipment is increased and the cost price is reduced.

By the late 70’s, FEA – Finite Element Analysis was limited owned by the aeronautics, defence, nuclear and automotive industries. Later, due to a impressive increase in computing power and a drop in the cost of computers, FEA was technologically advance to a very high accuracy. Nowadays, the computers have the capability to give precise results for all type of parameters.

FEA – Finite Element Analysis is one of the most dominant numerical methods used to check how the structure will react to certain loading conditions. Theoretically speaking, FEA is using a system of points called nodes that together create a grid called mesh. The mesh contains the material and structural properties that shows how the structure will react to certain loading conditions. Depending on the stress levels anticipated of a particular area, the nodes are assigned at a certain density all over the material. Generally a higher node density will be found in the areas that will receive large amounts of stress. The areas that will receive little or no stress it will usually have a lower node density. So, FEM provide detailed visualization of where structures twist or bend and gives precise indications of the distribution of stresses and displacements.

Testing

Dredge Yard related: ’’All our components are tested in Finite Element Analysis as one part after that all parts are assembled and tested under pressure and maximum movements. Worst cases scenarios are simulated and peak loads are applied. After analysis, the design might be reviewed couple of time to find out the most optimal shape and lowest stress in material. For wear parts, a Finite Element Analysis is run for worn out parts as well allowing our engineers to design the dredging components for the longest life time by adding material where necessary.’’

In summary, FEA’s benefits include enlarged accuracy, intensified design and enhanced perception into critical design parameters, virtual prototyping, amplified productivity and increased revenue.