The susceptibility to stress-corrosion cracking of the pipe metal of a long-term operated for 40 years main gas pipeline made of X70 steel and an emergency reserve pipe during cathodic protection in NS4 was investigated. A tendency towards some increase in susceptibility to stress corrosion cracking at a potential shift of -0.75 to -1.05 V was found for the serviced pipe compared to stock pipe metal. It is shown that the value of KS is slightly higher for the operated pipe, which indicates the possible embrittlement of the steel with long-term exposure to external cathodic polarization.