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THE EVER-GROWING IMPORTANCE OF ROBUST DREDGING HOSE SPECIFICATIONS
The dredging hose industry has seen great change in the last few years; with a significant influx of low-cost suppliers who have gone on to become small manufacturers. As a result, the price of hoses in the market place have been lowered by using cheaper raw materials. This move has increased hose failure rates, shortening product lifespans. Coupled with improper testing and lack of standards, hoses are becoming commodity products as opposed to the technical goods, that they once were.
Market shift
Over the last two decades, the dredging industry had relatively low numbers of manufacturers and only a few suppliers. This led to developing high-quality products that performed effectively and guaranteed longevity. Therefore, the specifications for the procurement of hoses at that time were not purposely designed for quality monitoring or consistency, as hoses were purchased by the bursting pressure and dimensional measurements.
Today, the quality of the hoses in the marketplace is becoming doubtful, and the traditional suppliers are losing their competitiveness. Due to the absence of adequate product specifications, it is becoming increasingly difficult to differentiate between a superior and an inferior quality hose.
Hose components and construction
Different types of hoses used in dredging applications are required to operate at various working pressures and the structure of the hose varies depending on the specific application.
However, all hoses have three essential components and the quality of a hose is primarily dependent on the quality of these main components: an inner layer for efficiency, an outer layer for protection from the environment and a reinforcing layer for strength.
Production method and machine
A precise production method is vital to achieving superior quality of hoses. Therefore, it becomes vital to understand the different steps involved in the manufacturing process. Critical manufacturing elements that need to be considered are:
· Quality of rubber compounds used
· Choice of polymer and quality of the reinforcement layer
· Pressure and angle of braids that ensure all layers are bonded well together to perform as a single unit
The manufacturing process of a non-floating (onboard) hose starts by fixing the steel flanges on the mandrill and then wrapping the inner layer, followed by the reinforcing and outer layers on the top of each other on the mandrill. The whole unit then goes into an autoclave to vulcanize the rubber and ensure all layers are bonded as a single unit.
The production process of floating hoses is different. In this process, the hose is cured twice under high temperature (+130°C to +150°C) and pressure, which causes deterioration in the physical properties of the rubber compounds. It is therefore crucial to ensure that materials are of superior quality because the degradation of properties is unavoidable.
Hoses in application
The lifespan of a hose depends on many factors. These include the nature of the material passing through it, application temperature and flow rate, to name a few. A superior quality of hose may last for several months to several years. The lifespan of on-board hoses is expected to be longer than floating hoses.
Usually, many floating hoses are connected to each other to make a long transportation line to convey the dredging materials from the seabed to a desired location. However, this makes the inspection of individual hoses difficult, which means the hose is at greater risk of premature failure. This therefore presents a risk to individuals on-board.
The bending of a hose creates extra stress and strain on the hose body. This can result in mechanical and chemical damage in a short space of time. The rubber quality and the manufacturing process is therefore vital to enhance the life span of hoses in such critical applications.
Different components: Properties and testing need
When it comes to testing, the properties of the hose’s inner layer are decided by the materials it will be used to transfer – this could be solids, liquids, gases, acid, alkaline, neutral or solid abrasives with high velocity. The polymer could be a combination of natural rubber, polybutadiene and styrene butadiene rubber. It should be resistant to different solvents, temperature, flame or fire.
It is vital to undertake testing for the rubber compounds to ascertain strength and elongation at break, hardness, and before and after aging. Tests should also measure tear strength, solvent and heat resistance, and abrasion resistance, to ensure these are high.
The base polymer for fabric material and number of layers are determined by the operating pressure of the hose. As a result, the bonding between the layers is crucial to ensure the hose can withstand pressure. At a minimum, the reinforcement layer needs to be tested for fabric strength and elongation at break, as well as bonding strength between layers.
The outer layer will be exposed to various environmental elements and therefore should possess oil, heat, ozone, chemical and oxygen resistance properties. It’s essential for the outer layer to have cut and chip resistance properties, and a high abrasion resistance. As a result, the choice of base polymer is important – Ethylene Propylene Diene Monomer (EPDM) rubber is the primary choice. The outer layer needs to be tested for strength and elongation at break, and hardness before and after aging, as well as tear strength, ozone resistance and abrasion resistance.
Final product inspection and testing
Typical tests include dimensional checks and visual appearance checks. However, these tests do not provide sufficient information about the performance and lifespan of a hose. Therefore, additional compound testing is needed to ensure the right materials have been used in the production process to support the aging effect of the rubber compound.
A best practice approach
Based on the properties needed for the different components of hoses, it is vital that the industry specify physical properties including tensile strength, elongation at break, hardness, abrasion resistance and tear strength. These need to be taken into consideration for inclusion in the technical specifications and be evaluated along with other common tests that are currently implemented.
Raising the bar for dredging hose specifications
Hoses are a critical component of the dredging process. Unfortunately, neither the production process nor the testing of hoses is regulated by any international or national standards, or industry guidelines. Sometimes hoses are purchased to customers’ own specifications, which are neither robust nor stringent. It is therefore becoming easier for manufacturers to take advantage of the lack of existing standards and supply low-cost, low-quality solutions. Though the pricing may be attractive to the end user, usage experience will be at risk.
The quality and reliability of hoses are difficult to ascertain in the absence of standardized tests and specifications in this industry.
Specifying rubber compound properties and fabric construction will be a great leap forward towards establishing robust product quality by taking care of the rubber components from the very beginning of the manufacturing process.
The recommended properties can be used as guidance to develop stringent technical specifications that ensure quality products are supplied in the industry to meet the needs of clients and raise the industry bar.