English to French Tech/Engineering Petroleum Eng/Sci drilling

Bonjour,

savez-vous ce que signifie "casing of pipe" dans la phrase suivante ?
"We have an auger. A little drilling rig comes in, drills a 40 inch, 40 inch hole.... And we drill X amount of hole with it, then we line it with a casing of pipe, and then we have two or three other different sizes and we wind up with this eight and a half right here, the little one."

Il s'agit d'un texte parlant de forage.

Merci d'avance !