MAKING LIQUID TRANSFER SAFER

Asked to name dangerous industries, few people would include food and beverage manufacture. However, as FlexRite Chemgiene points out, these industries account for around a quarter of all industrial injuries. The incidents which give rise to these injuries take many forms, but a significant percentage involve road tankers which after delivering or receiving liquid products, drive away without uncoupling the hose that connects them to the fixed plant.

A breakaway incident of this type can have a whole range of serious consequences. Tension in the hose before it snaps can cause extensive damage to both the tanker and to the fixed plant, resulting in costly down time, and substantial repair costs. The hose will almost certainly be destroyed and, even worse, when it finally parts as the tanker moves away, it is likely to whiplash, creating the possibility of serious injury to persons in the vicinity.

In theory, it should be possible to eliminate breakaway incidents simply by implementing and enforcing good working practices. In reality, however, some risk will always remain, especially as today’s working environment creates pressures for tankers to be turned around in the shortest possible time. Clearly, there is a need for some form of automatic fail-safe preventative system.

In principle, implementing such a system should be straightforward. All that is needed is a hose coupling which will pull apart when the tension in the hose rises above a predetermined level. Analysing the requirements more closely, however, quickly shows that designing a coupling that has the necessary qualities is actually far from easy.

It is a requirement that has been successfully addressed by FlexRite Chemgiene with its Salamander hygienic breakaway couplings. Designed specifically to meet the requirements of users in the food and beverage industries, these innovative couplings combine the tried and tested qualities of the tri-clamp type gasket with the hygienic properties of 316L stainless steel. The couplings are available in 2”, 2.5” and 3” versions to match all commonly used tanker discharge hoses and they can be used with virtually any standard hose end.

Hose couplings must part reliably at a pre-defined level of hose tension, which must be sufficiently low to minimise the risk of any serious whiplash effect. However, it must remain intact under all normal operating conditions, and also when subjected to the rough handling that hoses invariably receive.

Further, the separation performance should be maintained throughout the coupling’s working life, preferably without the need for maintenance, and it should be possible restore that performance easily and reliably after a separation incident, so that the coupling can quickly be put back into service.

Many design approaches are possible, but the one that best satisfies the above requirements at an affordable price is based on the use of specially fabricated connector pins to hold the two sections of the coupling together. In a practical design, these are precision-machined components, the key feature of which is a narrow waist.

At a certain level of tension, these pins start to stretch at the waist. As they do so, the waist narrows still further and the pin stretches increasingly easily. The net effect is that once stretching has started, it proceeds almost instantly to the point where the pin fractures. The breaking tension of the pins is, therefore, very well defined. This means that the couplings in which they are used also have a well-defined parting tension. This can be chosen to be significantly higher than the hose will experience in everyday use, but lower than the critical whiplash tension. Provided that they are manufactured from corrosion-resistant material, the pins will not significantly degrade with age, however long the coupling is in service. In addition, after a breakaway incident, the coupling can easily be brought back into use simply by fitting new connector pins, and its performance is then guaranteed to be equal to that of a brand new product.

While the connector pins are the key to the design of a reliable and effective breakaway coupling, in a practical product there are other important factors which must be considered. The material from which the coupling is manufactured must, for example, be resistant to corrosion and compatible with the products that are being handled. For applications in the food and beverage industries, 316L stainless steel is a suitable choice.

In those industries, hygiene is, of course, also a prime concern, and this means that the couplings need to be carefully designed to eliminate crevices and traps that might otherwise harbour stale product or contaminants. Also, in many cases, the coupling will need to be capable of withstanding the high temperatures, sudden temperature changes and aggressive chemicals which are associated with cleaning in place (CIP) procedures.

Finally, however good the couplings, they are of little value unless they are compatible with the hose fittings which are used by the customer. The best breakaway fittings should, therefore, be available in a variety of standard sizes, ideally with an option for them to be adapted to suit proprietary end fittings.

Breakaway incidents are one of the most common problems associated with the transfer of liquids to and from road tankers. They can have expensive, inconvenient and more importantly, dangerous consequences, but are easily eliminated by using well-designed breakaway couplings. Types based on breakable coupling pins are recommended, as they offer the best combination of reliability, performance and value for money.


REF: FLEX037

<< Back >>