Season cracking

The problem of season cracking is known from brass cartridge failures during the monsoon season in India in the 1920s, failures which were caused by attack of the metal by ammonia. The edges of rifle cases cracked and could cause misfiring of rifles. The gas was produced from animal manures during the high temperatures and humidities of the monsoon, and by the high levels of residual stress produced by forming the barrels of the cartridges. As a type of stress corrosion cracking, it is characterised by deep brittle cracks which penetrate into affected components. If the cracks reach a critical size, the component can suddenly fracture, sometimes with disastrous results. However, if the concentration of ammonia is very high, then attack is much more severe, and attack over all exposed surfaces occurs. The problem was solved by annealing the brass cases after forming so as to relieve the residual stresses.

Ammonia

Attack takes the form of reaction between ammonia and copper to form the cuprammonium ion, a chemical complex which is water-soluble, and hence washed from the growing cracks. So the problem of cracking can also occur in copper and any other copper alloy, such as bronze. The tendency of copper to react with ammonia was exploited in making rayon, and the deep blue colour of the aqueous solution of copper oxide in ammonia is known as Schweizer's reagent.

Materials

Although the problem was first found in brass, any alloy containing copper will be susceptible to the problem. It includes copper itself (as used in pipe for example), bronzes and other alloys with a significant copper content.

ee also

*Brass
*Environmental stress fracture
*Forensic engineering
*Stress corrosion cracking

External links

* [http://www.corrosion-doctors.org/Corrosion-History/Eight.htm Forms of corrosive attack]
* [http://www.meic.com/Newsletters/1999/Summer99.htm Cracking of Manganese bronze by ammonia]
* [http://www.designnews.com/article/CA6458214.html Cracking of a copper pipe]
* [http://ecow.engr.wisc.edu/cgi-bin/getbig/msae/433/1hellstrom/lecturenot/www.npl.co.uk-lmm-docs-stress.pdf National Corrosion Service in the UK]
* [http://openlearn.open.ac.uk/mod/resource/view.php?id=233628 Season cracking in the Indian Army]