Preheater mounted within a well

A heater assembly for insertion into and withdrawal from a tube curved along its length, said heater assembly comprising:

• a generally hemispherically shaped heat resistant head means for engaging the inner surface of said tube and following the lengthwise curvature of said tube during the insertion of said assembly;
• core means for withdrawing said head means from said tube, and comprising a heat resistant material attached to said head means and extending substantially the entire length of said assembly;
• flexible housing means for enclosing said core means in spaced relation with said housing means and comprising a heat resistant material tightly wound into spiral turns to provide a generally tubular configuration having substantially smooth internal and external surfaces, said housing means attached to said head means and extending substantially the entire length of said assembly;
• electric means for heating said tube, said heating means unitary with said assembly and extending along at least a portion of the length of said assembly;
• said core means and said heating means having the characteristics of bending substantially in unison with said housing means along the length of said assembly during insertion into and withdrawal from said curved tube to retain a spaced relation from said housing means;
• and said core means further comprising means for opposing substantial separation of said spiral turns during said withdrawal.