The Effect of Welding Electrode Composition and Storage Temperature on SCC of Carbon Steels in Liquid Ammonia

Abstract Stress corrosion cracking of welded carbon steel in liquid ammonia was studied with bend specimens made from carbon steel plates welded with different welding electrodes. Three electrodes commonly used for construction of ammonia storage tanks and one recently developed low strength electrode were studied at ambient temperature. The low strength electrode was least susceptible to stress corrosion cracking of the four electrodes investigated, while the welding electrode containing nickel seemed to have a somewhat higher susceptibility than the other electrodes. The susceptibility to SCC increases with the strength of the weld metal. The high susceptibility of the nickel containing electrode remained after heat treatment, indicating a possible detrimental effect of nickel. The effect of temperature on SCC of carbon steel in ammonia was studied with parent material compact tension specimens and bend specimens with welds. The experiments were performed at -33°C, where many refrigerated ammonia storage tanks operate. The results were compared with results from experiments at 18°C. It is much more difficult to initiate stress corrosion cracks at -33°C than at 18°C, and crack growth is slower at low temperature. The ratio between maximum crack depth in comparable experiments at -33°C and 18°C was 1:3 for CT specimens and 1:20 for bend specimens. Practical experience shows also that SCC of carbon steel in ammonia can occur at low temperature, but to a much lesser extent than at ambient temperature.