Each pneumatic conveying systems has them, Bends. They determine the routing of the pipeline, but they could be a pain in the neck for the maintenance crew.
During the lifetime of a bend, some require attention every week or months, while others are placed once and will last a lifetime, how is this possible?
There are 2 critical aspects that have a big influence on the durability of the bends;
- Design of the conveying system
- Type and size of bend
Design of the conveying system
Thanks to the use of bends, we are very flexible in the design/routing of the conveying system, which is a big benefit.
When looking in the durability of the bends in a conveying system design there are three pillars;
- Pressure drop
When powders flow through a bend, a so called “pressure drop” will occur as a result of resistance to the flow. This friction loss will be generated by each fitting, bend, valves and all other components within the pipe routing. This pressure drop can be expressed as a equivalent in length of extra pipeline.
The cargo particle velocity has huge impact on the wear and tear inside the bends, once to velocity is too low – a blockage will be generated as the particles won’t be transported anymore, but once the velocity is too high – it will dramatically influence the wear and tear. So an optimum balance need to be found between velocity and wear.
The internal surface of the bends are deteriorating due to the abrasive movement/actions of the cargo particles hitting the bends during directions change. The exact location of excessive erosion depends on multiple factures and could be determined/predicted based on knowledge and experience;
Type of Bends
There are numerous types of bends, as each has its own pros and cons, there is no bend design that fits all purposes/applications.
- Type (besides the common radius bend)
The radius of the common type of bend, has influence on the resistance, velocity impact of the cargo, travel distance, etc. As the very long radius bend has a low impact on the resistance as the cargo direction change is brought to a minimum, unfortunately the travel distance of the cargo is now longer against the short radius bend. Test results for bends used in the powder bulk convey industry, have shown that a balance between pressure drop, erosion and needed energy for conveying, a type 3D bend (of the shelf “short” radius) is appropriate and economical the finest selection, whereas bends bigger than 3D have less pressure drop, the distance of the cargo need to travel is also longer and influence negatively against the overall convey distance and her energy needed to convey it. Besides the fact that such type of bends are less common and therefore more difficult to get access to, which also raise the investment costs.
A variety of materials can be used during the production of bends, also a different type of surface treatments are offered, all to influence the friction and/or lifetime. As costly materials are used to increase the lifetime, customers do often prefer the cheaper type of materials (common gray iron or carbon steel) as they are easier to get on the local market and will last for example only half the lifetime of the expensive type. However investment wise this might be identical, however such decision has impact on the operational costs, as the pipeline encounters now 2x down time for the replacement vs 1x for the expensive type of bend.
Bends are the most significant part of the convey system and requires the highest attentions during routing design, which influence heavily on the operational costs as they absorb the most energy.
An overkill on the amount of bends for the sake of “looking” good in the application or a wrong selection of the bends material, could end up in dramatic convey results.
Do you would like to know more about bends or would you like to improve the efficiency of your material handling system, contact us via our contactform.