Trepanning is the process of taking a large Bar and converting it to a tube and is commonly used for the Oil and Energy industries. In some cases an Inner Diameter may be impossible to find for Tubing which is what makes Trepanning an option in sourcing Large Tubes (see image)

Trepanning is a process that will generally have a lead time of 1-2 weeks in addition to Boring to specific tolerances to ensure precision.