The process of hot tapping, sometimes called pressure tapping, is one in which a connection is made to an existing pipeline or other type of pressure vessel without the need to empty it. That means the operational capabilities of the pipeline can continue without interruption while the modification of maintenance is carried out.
In certain circumstances the method is also used to drain off pressure that is unwanted or is causing a problem to the normal operation of the installation.
The 'hot' aspect doesn't necessarily refer to the temperature at which the process is carried out though and is used more to describe the same way that a USB stick or other storage medium can be plugged in, and removed, from a computer without turning it on or off.
Hot tapping is often used to make repairs where corrosion or other types of physical damage have occurred to systems, although it can also be used in modifications or upgrades to add branches to an existing network.
The ability to make these changes without releasing pressure and venting pipes and pressurised systems means that not only is operational service uninterrupted, but environmental concerns surrounding such measures can be addressed adequately.
There are some situations where hot tapping is impractical or dangerous, with the risk of burn-through, unstable decomposition of the flowing product, and hydrogen cracking all possible complications.
Burn-through is a potential situation whereby the pipe being worked on doesn't retain enough viability to contain the pressures inside. Unstable decomposition of the flowing product can cause violent reactions when heated under pressure.
The risk of hydrogen cracking is increased by hot tapping because the flowing product can increase the rate of heat flow from the weld region, leading to shorter cooling times and a risk of hard microstructures forming and then causing hydrogen cracking.
To avoid this, gaseous mixtures in which the partial pressure of hydrogen exceeds 700 kPa gauge usually mean hot tapping is not safe. The only exception is where evidence from tests demonstrates otherwise.
Without the use of hot tapping, production would have to be shutdown to expand your pipe network bringing all the commercial and environmental impact that would accompany it. This makes the process a particularly valuable one where it is possible to implement it.