Composite materials in industrial valve applications
Rene van der Gaag, Product Manager for special service valves, Tyco Flow Control
Traditional valve construction materials – iron, stainless steels and metal alloys - whilst still providing a robust choice for the end user, no longer represent the preferred choice for the water industry. Advances in polymer technology have produced a range of thermosetting polymers and thermoplastics with robust mechanical properties, allowing them to be engineered as alternative components. Using composite materials for components impacts on design, performance, cost and sustainability characteristics - all issues influencing the specification of flow control valves.
In recent years, rising raw material costs for traditional valve materials have led to a gradual relocation of noncritical manufacturing processes. A combination of experimentation with cutting-edge technologies and a greater understanding of their chemical and physical properties has seen composite material technology specified and installed by both engineering consultants and contractors with far greater confidence.
Composite materials have made huge progress in recent years. Their improved mechanical properties, as well as their chemical and physical behaviour, now deliver comparable performance to traditional metal resilient seated butterfly valves, demonstrating significant benefits for the industry.
The major benefits
New materials call for new ideas. The adaptability of composite materials shape every element of design and it is now possible to eliminate material where it is not needed to create hollow sections within the valve body. Whilst some plastic valve designs already employ hollow sections, these are on the exterior of the valve body which can allow dirt and dust to collect.
Composite materials provide a good fit in meeting the industry’s sustainability requirements, both through a reduction in metal raw materials, and low mass and low thermal conductivity of the material which offers considerable savings in energy, manufacture, transport and application.
To take a specific example (that of quarter-turn industrial butterfly valves) the improved mechanical properties of composites and their chemical and physical properties ensure that they can deliver performance that is comparable to - or better than – a metal resilient seated valve and additionally offer reduced weight and better corrosion resistance.
In fact, the examination of important characteristics such as tensile strength, elongation and modulus permits composite valve construction that performs more like traditional valve materials than the conventional plastics to which composites are sometimes mistakenly compared.
The choice of low mass materials such as composites offers a number of significant benefits in terms of finished products. In valve applications there is the possibility to reduce the number of structural pipe supports in a typical process installation, especially when connected to plastic tanks or pipes, and also makes the valves suitable for plastic pipe lines. Further benefits are obtained in lower fuel consumption costs during transport from the production plant to the site and lower installation costs.
With regards to chemical resistance, this can be measured in comparison to stainless steel, with the best-performing solution ultimately dependent on the application in question. For example, high and mid-range composites demonstrate outstanding performance in harsh or aggressive environments. Furthermore since corrosion resistance does not require additional protective layers or paint which could be damaged by impact, the maintenance requirements of units over their lifetime are reduced.
Additional benefits also includes low thermal conductivity and the presence of internally reinforced, hollow-body sections which enable a reduction of process heat loss and eliminates the need for lagging, heat tracing or valve jackets. In addition the low thermal conductivity also reduces the risk of process freezing or flow problems that arise from heat loss.
Innovation from the industry leaders
Research by Tyco Flow Control and its partners led to a blend of two thermoplastics which offered exceptional design flexibility and an opportunity to improve both shaft and disc design. This development resulted in Tyco’s Keystone CompoSeal® range of butterfly valves featuring a composite body and disc-shaft assembly. An immediate benefit of this innovation now enables composite valves to be designed with a one-piece disc-stem, minimising hysteresis problems between the shaft and disc. This makes a valve suitable for regulating as well as on/off duty, and ensures the shaft remains dry to eliminate crevice corrosion between the shaft and disc.
Tyco Valves & Controls
Tel: 01858 467281
Published in Valve User Magazine Issue 20
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