I am investigating a nitrate SCC failure (mechanism is confirmed) in a heat exchanger. The temperature of the system is approx. 90 - 100 ºC and the tubes are manufactured from a carbon steel. Since literature is rather vague about crack propagation rates - what are the (typically) lower and upper limits that I can expect in such a system?
Kind regards
Felix Lampert
Felix
You have not much said on the material used for heat exchanger neither the concentration of nitrate. Carbon steel has been used in manufacturing heat exchanger, but whether it is low or medium carbon steel, heat treated or annealed stress relieved and time frame of failure. If a micrograph is put with question, it would be of great help.
Generally, the concentration of nitrate varies, if it is 5% nitrate in solution, then it would take, say at 100C, about 6 to 12 months for crack to origin and failure would occur within 12 months, depending the tube diameter, design configuration, and so on. For higher concentration of nitrate in solution, say 20%, the crack would start within 40 to 90 minutes and failure would occur within 200 to 300 minutes. Hope this helps
Dr. K
Felix
Possible to supply details of the failure of heat exchanger. This help in giving the correct solution, although SCC is notorious with the changes in operational and surronding environment conditions. Failure photos and micrographs would really be help in solving your problems.
Dr. K
Hello Felix,
would checking the literature on environmental assisted fatigue crack propagation rates and the K values for such systems help?
Viswes
Yes, it would help if you find the value in the literature that is identical to your setup, then, it is possible to postulate the crack propagation rate with some errors, as your experimental setup could not be exactly identical to the set up and the value found in the literature.
You could also set up the experiment as reported in the literature and see whether the value of the fatigue crack propagation are the similar or close to that reported in the literature. This way it would help in varification. Hope this helps.
Dr. K
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