Copper Stress Corrosion Cracking

Copper alloys have different behavior regarding the possibility of a SCC in ammonia environments, so i don't think that is possible to define a general safe limit for all the alloys due the influence of different factors as you said.

For example i've found on Shreir book that in general the susceptibility to SCC of Brasses appears to increase with increase in zinc content. Is possible to make also test but this doesn't guarantee the freedom from cracking in ammonia environments.

In my opinion you have firstly to define the type of alloy and then look if there are some literature data or previous experience to support you Materials Selection.

hope this help

Strider

<but is there a safe concentration limit at which all alloys are immune to cracking?>

No safe Threshold exists.

The short answer to your question is no. The reaction between copper alloys and ammonia has no threshold below which no reaction occurrs. In other words, it can happen with very low concentrations and long times. But wait, there's more! Tensile stress in the alloy greatly accelerates the corrosion process. This includes residual fabrication stresses. The British learned this when they tried to reuse ammunition brass that had fallen on the earth in India.

I believe trace elements can improve the situation along with picking an alloy with less than 12% zinc. Helpful additions are: Antimony, Arsenic, Phosphorus, and Tin?

Scott Shjefte