The paper reports the state of casing material of motor car highlift fuel pump destructed during operation. With the purpose of the material study on defects existence in the structure there is carried a metallograph analysis of cap material in an inlet valve. The investigation of nonmetal inclusions was carried out in accordance with the requirements of RSS 1778-70. At the same time there was carried out the investigation of a sample microstructure. The analysis of the totality of destruction facts revealed allowed drawing a conclu-sion that a casing destruction in a HLFP took place in the area of a lower turn of cover thread of one of inlet valves. It is established that the destruction occurred as a result of crack formation and its growth. A crack arose in the course of operation as a result of edge brittleness in metal grains caused by the development of corrosion cracking processes development.