Abstract: A sectional heat insulation jacket comprises a set of multi-layer insulation sections in which the layers are bound together by a fastening and fixing device. Adjacent insulation sections connect and they separate by assembling joints that are self-sealing. A mutual position of the adjacent sections is reliably fixed by the connecting device at each stage of heating. The self-sealing is accomplished by side flexible layers which incline under a sharp angle to the surface of an upper flexible layer. The sizes of the assembling joints between adjacent sections at levels of the upper and the bottom flexible layers are equal to the temperature expansions of these layers in longitudinal and transverse directions, correspondingly under the insulated entity's heating until an operating temperature is reached. A conical, helical spring shaped fastening rod further increases a length of metallic inclusions with high thermal conductivity form an insulated entity and reduces heat loss.