Inflatable plugs for line stopping in water networks

Inflatable bags live water pipes flow stopping

Water flow in pressurized pipes is a rather complex operation: static pressure, dynamic pressure and collateral effects (peaks, water hammer, resonances, …) combine to form a complicated environment that isn’t easy to understand. Major risks involved in an under pressure water pipe are not those ones associated with fluid’s composition: pressure and flow speed generate a high potential energy that can be the origin of severe problems. Grupo Torre‘s experience allow for operations under complex environments, with satisfactory results.

Technical backgrounds

Flow stopping in a pressurized live water pipe needs to previously determine working parameters of that flow. On one hand there is the static pressure, consequent to fluid impelling pressure (pump, gravity) and on the other one there is the dynamic pressure, consequent to flow’s speed. Fluid flow constitutes a moving mass which kinetic energy is a function of its speed, and also of its mass. This energy is proportional to the squared speed: speed increase means an enormous increase in kinetic energy. Associated to this energy we meet a set of consequences such as pressure peaks, water hammer, shock waves, resonance phenomena, … which makes situation even more complicated. Compared to gas flow stopping the major difference is that gas very easily inflamates and explodes and water no, but on the other hand, water has a 1300 times bigger mass than gas and thus kinetic energy is 1300 times bigger. This is the main reason of water flow stopping being more complicated than gas stopping. Another consideration is that water is an incompressible fluid, while gas is compressible. A compressible fluid acts as a buffer for pressure peaks and waves, but an incompressible fluid transmits any pressure change entirely and without any gap.
There are two different flow types we want to consider: laminar flow and turbulent flow. First one represents a “well organized” flow showing regular layers, and this makes it a more predictable flow, while turbulent flow is a disorganized status with a far less predictable behavior.
From all aspects we have been discussing, we can say that flow stopping operations in static systems /water under pressure but not flowing) are relatively less complicated, but when it comes to “live” systems (water flowing) thinks tend to be rather complex.
Ex.: in a water flowing pipe, with speed changing from 0 to 1,2 m/sec, dynamic pressure change consequent to speed is as shown in following chart:

 
Ina 300mm pipe, with a static pressure of 4 bar and 0,8 m/sec speed, we get 3,2 more bar which amounts to 7,2 bar overall (static plus dynamic) pressure. Mechanical load to be supported by stopping system amounts to more than 5 mT. If we now consider associated occurrences (mainly water hammer and pressure peaks) real case study shows us that pressure under these circumstances can multiply by 3 or 4 at least. This means peaks could rise up to 15 or 20 bar pressure, with a total load of 15 mT or more.

Flow stopping with Torre^® technology

Grupo Torre has developed appropriate technologies enabling to perform flow stopping operations in different fluids types, using sophisticated bags designed for high performance. Water flow is being stopped up to 6 bar and 1 m/sec.
Guidelines for Grupo Torre developed technologies are to be found in thoughtful analysis of performed real operations and operations performed in real size testing facility in factory.

Technical aspects

As we already mentioned, loads on stopping systems demand for sturdy design, and the consequence is heavy materials dimensioning. This would produce difficult to operate equipment because of the weight. Grupo Torre has put great attention in choosing materials that would allow for lower dimensioning and this has lead to not to heavy equipment.
Considering different situations that can concur, Grupo Torre has designed different bag types. Besides pressures consideration (both inflation and flow) bags materials have been chosen to get the highest possible friction coefficient between bag and inner pipe surface.
Bags structure is different for each application. It depends, among other, of relation between static and dynamic pressure. If only static pressure has to be addressed, bags can be used capable of withstanding tenths of bar pressures, but if dynamic pressure is considered, we need a special cross linked structure bags that enable to face speeds of up to 1 m/sec. These are only some factors affecting bags choice that has to be made for each operation.

 
If supply has to be assured, a by-pass is previously installed by means of Torre^® under pressure branching systems.