Glossary

The intrados of a tube or pipe is the inside surface of a bend, located on the inner radius of the curved section. It is the side that follows the shortest arc length through the bend, so during bending it is placed primarily in compression rather than tension.

Because the intrados is compressed, it tends to experience different (and often opposite) effects than the extrados. The wall at the intrados may thicken slightly as material is pushed together, and it is the area most susceptible to wrinkling, buckling, or wave formation—especially with tight bend radii, thin-wall tubing, insufficient internal support (mandrel/wiper), or poor process control. In induction bending and other hot-bend methods, intrados behavior is also watched because compression plus temperature effects can influence local shape stability, ovality, and surface condition.

Intrados is commonly referenced in bend specifications and inspection reports alongside the extrados (outer radius) because many bend acceptance limits consider the combined outcomes of intrados wrinkling, extrados thinning, and overall ovality to ensure the tube meets dimensional and performance requirements.