In practice, coiled pipes working under extreme conditions in furnaces for pyrolysis of hydrocarbons may have all types of defects of various natures. These defects may stimulate generation of cracks. A distinctive feature of the process of pyrolysis is accumulation of by-product, coke. This deposition of coke at the inner surfaces of pipes is the reason of aggressive diffusion of carbon into wall’s structural material, high-alloy steel. Due to the technology of pyrolysis, structural material works under high temperature up to 1000o C. At that, the thicker a layer of the coke at the inner surface of a pipe, the higher the temperature required. High temperature results in decarbonization of the external surface of pipes and intensive generation of pores that are corresponded to the creep mode. As a result, we arrive at quasi-multilayered shells and properties of these layers differ drastically.