By Reid Penner
Thoughts on Temporary Piping Restraints
The province of British Columbia is in the process of adopting new regulations with regards to the use of restraint systems for temporary piping around well sites. If Alberta was to adopt a similar stance on piping restraints, there could be major changes to what can be described as an adequate temporary piping restraint system. This could result in an increase in set-up and tear-down times on well sites, as well as more training on these systems. Therefore it is becoming more and more important to develop quick, simple, and effective piping restraints, and to understand what the effects of a pipe bursting are and how they can be dissipated safely.
For these temporary restraint systems, many companies are starting to use synthetic polyester round slings. These slings provide the benefit of being easy to store, easily acquired, and are simple to deploy and operate in the field. In calculating the forces acting on these round slings during a piping burst, there are several assumptions made in how they will be deployed. For example, the slings must be pulled tight, such that there is as little slack as possible in the lines. As well, the slings are to be tied to the pipe string in regular intervals. This would ensure that in the event of a burst, the sling would be subject to as small as possible shock load, and that the pipe would be given very little room to whip around. Set-up of such a system would require selecting the right sling based on the working pressure and pipe diameter, then anchoring the slings to the temporary piping and to an anchor, such as an existing support or wellhead.
The Worst Case Failure of Pipe Bursting
The worst-case failure of a pipe bursting would be if the pipe was severed around the circumference. In this case, there are two sources of force acting on the restraint system. The first is the initial separation force of the pipe, given by the pressure in the pipe acting on the cross-sectional area of the pipe itself. This is the same as a cork popping out of a champagne bottle, and accounts for a smaller portion of the burst force. The second is that the pressure in the pipe will force the internal fluid out of the newly formed hole, exactly like a rocket. According to Newton’s 3rd Law of Motion, the force that the fluid leaves the pipe is exerted on the pipe itself, and in turn transferred to the restraint system. Therefore, a good general rule is that a liquid in the pipe will exert much more force during the burst than a gas at the same pressure, due to the fact that the liquid is denser.
However, gas-filled lines become more complicated in how they burst. Because the mass of the gas is much less than the liquid, the gas is accelerated to a much higher burst velocity (For pressures above 15 psi, the gas will be moving faster than the speed of sound). This means that while there is less force exerted on the restraint system, the burst is accompanied by a large pressure wave.
The Difference Between A Liquid Burst Versus A Gas Burst
The differences between a liquid burst and a gas burst are quite startling. If a liquid burst is like a rocket with a directed pressure stream, a gas burst is much more like a bomb. The main danger in a burst with a liquid medium is that the pipes will whip around, which is why an adequate restraint system is very important. In a gas bursting case, much less energy is transferred into the pipe, and it will move less. A restraint system is still imperative to stop any whipping of the pipe, but the danger comes from the large shockwave of the escaping gas. This pressure wave can propel smaller debris, like pipe fragments, up to large speeds. As well, the pressure wave itself could also lead to bodily harm. As such, a gas bursting scenario is more dangerous than a liquid burst, mostly because much of the energy can’t be managed with the pipe restraint system.
What Does This Mean For Well Site Operations?
In these tougher times, there can be considerable pressure to complete well site operations as quickly as possible. With the hint of stricter regulations on the horizon, this task has become a little more difficult. However, with the danger that is present from pressurized temporary piping, a restraint system for those lines cannot be the component that suffers. With these thoughts in mind, development of quick, simple, and effective restraint systems for temporary piping runs will be an important step in moving forward.