What is Cold Springing or Cold Pull?
Cold springing or cold pull is an engineering approach used in piping systems to intentionally deform the pipe (thus inducing pre-established stresses) during the installation stage (when the pipe is cold/ or at ambient temperature) to compensate for expected thermal expansion or contraction (when the piping system is exposed to the higher temperature).
Assume, when a piping system is exposed to changes in temperature, the pipe materials expand or contract accordingly due to thermal expansion. If this expansion or contraction is not accounted for these changes, excessive stress can be generated on the piping system, leading to potential failures and leaks.
To prevent this, piping engineers use the technique of cold springing to intentionally deform the pipe during installation, so that when it experiences thermal expansion or contraction, it will return to its intended shape and position.
How Cold Springing is applied in Piping jobs?
Engineers use a physical approach to achieve cold springing, i.e., the piping system is initially installed with a slight deformation in the opposite direction of the expected thermal expansion or contraction. This deformation is then released once the system reaches its operating temperature. The amount of deformation, or “cold spring,” required is calculated based on the expected thermal movement and the properties of the pipe material.
The amount of deformation, or “cold spring,” required for the effective cold pull is typically around 50% of the expected thermal expansion or contraction of the pipe run under consideration. This calculation takes into account the properties of the pipe material and the anticipated changes in temperature.
Why Cold Pull or Cold Spring is used in Piping Systems?
Cold springing is a technique that is used to minimize the maximum thermal loads and stresses in a piping system. This is accomplished by introducing a predetermined level of stress in the pipe while it is cold. The primary goal of this technique is to reduce the peak loading on connecting equipment.
However, it is important to note that cold springing does not have any effect on the overall stress range in the piping system. As a result, it cannot be factored into stress range equations. If a piping system is operating well below the creep range, any cold spring applied during the initial installation should remain effective for the life of the system.
On the other hand, if the piping system is operating within the creep range, any cold spring applied during the initial installation will eventually fully relax out. This means that the pipe will become 100% cold sprung, regardless of how much cold spring was applied during the original build stage.
Some codes, such as BS806, utilize cold springing to minimize the maximum hot stress, which is the sum of deadweight, pressure, and thermal expansion stresses.