Patent ID: 8225864

Claim:
A wellstring assembly comprising: first and second tubular casing members, each having a threaded end; a coupling having an outer diameter greater than the casing members that secures the threaded ends of the casing members together, the coupling defining a shoulder on one end; a tubular device including a bore therethrough, the tubular device installed on the first casing member with the first casing member extending through the bore, the tubular device comprising: an outer shell having an exterior surface with a plurality of ribs extending radially outwardly from the exterior surface of the outer shell, the outer shell having an interior surface with recesses opposite and in conformity with the ribs, the outer shell being of uniform thickness and formed entirely of a sheet of steel; a body located within the shell and having an exterior surface that is in contact with and in conformity with the interior surface of the shell, including the recesses, without any gaps between the exterior surface of the body and the interior surface of the shell, the body having a first end and a second end, the first and second ends extending circumferentially about the bore, the bore being in physical contact with and axially slidable on an exterior surface of the casing member relative to an axis of the casing member; the body being formed entirely of a polymer; and the outer shell having first and second ends, each having an inner diameter smaller than an outer diameter of the shoulder of the coupling so as to abut the shoulder in the event the body and the shell move axially on the first casing member a sufficient distance.