The paper deals with the determination of corrosion rate to the natural gas pipeline API 5L X60 in Trnava region. Linear polarisation resistance method (exposure time 1 hour) was used for investigation the corrosion rate of exposed samples in the environment (top, middle and lower part of soil excavation and distilled water). The corrosion rate was also determined by measuring the weight loss of the steel samples. The exposure time for the measurement method of the weight loss of metallic materials accounted 120, 288, 528 hours. These outputs helped to identify the most suitable environment for the tested metallic material. Top and middle part of soil excavation was situated in the least aggressive environment. On the other hand, the lower part of soil excavation was situated in the most aggressive environment for API 5L X60.