Hot tapping strictly refers to the installation of connections to pipelines while they remain in service. In the welding context, it is commonly used for any welding onto in-service equipment. Hot tapping is frequently used in order to repair areas that have undergone mechanical damage or corrosion, or to add branches for system modifications. There are distinct economic and environmental advantages to performing this welding without removing a pipe from service and possibly venting quantities of greenhouse gases, such as methane.
Safe procedures for hot tap welding can be devised using computer heat flow modelling techniques, and qualified using flow loops. Part of this approach is to match and/or control the cooling capacity of the live pipeline, for which measurement techniques are available.
Mechanical fittings may be used for making hot taps on pipelines and mains provided they are designed for the operating pressure of the pipeline or main, and are suitable for the purpose.