Keyword: «fatigue failure»

In article the review of scientific theories of fatigue failure of constructional materials is executed. Their short characteristic is given and the comparative analysis is made. The reasons of shift processes in material and kinetics of origin of fatigue cracks are considered at influence of cyclic loadings. Prospects of development of engineering calculations for this direction of researches are planned.

Drilling of new fields is associated with certain difficulties, mainly the harsh climatic conditions of the Arctic and ultra-long wells. These conditions have a negative impact on traditional steel drill pipes because steel has a cold-fracture threshold and low specific strength. The effect of the scale factor on the fatigue properties and fracture mechanisms of drill pipes made of aluminum alloys D16T and 1953T1 and steel of strength group G-105 has been experimentally investigated. The values of the endurance limit during multi-cycle testing of samples and the fatigue life of drill pipes during full-scale field tests for materials have been determined. A significant reduction in the fatigue characteristics of materials during field tests has been established. It is shown that drill pipes made of aluminum alloys meet the requirements for pipes made of steel of strength group G-105 according to API RP 7G and have a significant advantage in specific characteristics compared with steel pipes, which is especially important during development and drilling in the Arctic regions.