Cracking in Brass Tubes (Ammonia, Annealing, etc) 2

[Binary]

Hello.

We've got some brass tubes (C26000 & C27200 - 1" & 1-5/8" OD x .065" wall) that are used in antennas that have recently come back from the field with longitudianl cracks after only a few years.

Communication is lacking somewhat but apparently somebody has determined that atmospheric ammonia has somehow degraded the material. They say that annealing the tubes should solve our problem.

I'm looking for guidance here.

Specific questions:

1) Does the atmospheric ammonia theory fly? (I'm not clear if they've actually ID'd NH₃ in the samples)

2) Are we using the right alloys?

3) If it's ammonia, will annealing solve the problem?

Any other suggestions or guidance would be appreciated.

 

[Binary]

OK, I have more information which answers some of my own questions. I'm posting just so others might benefit someday??

From descriptions I've read, what I'm seeing is stress corrosion cracking. Apparently ammonia can contribute but is more likely to be residual stress from coldworking.

Alloys with less than 15% zinc are less susceptable - C23000. Only potential downside is lower Fy at 44 ksi (not an issue in my case).

A stress-relieving anneal (1 hr @ 500F) should resolve issue as well.

I'm still interested in this ammonia thing. Does anybody know the cause?

 

[Carburize]

When an alpha brass is subjected to an applied or residual tensile stress in contact with a trace of ammonia or in contact with a substitute ammonia (amine), in the presence of oxygen (or other depolarizer)and moisture, it cracks along the grain boundary (intergranular). Cracking through the grains (transgranular) may occur if the alloy is severly deformed plastically.
Problem was originally observed by the British army in India as cracking in brass cartridge cases - since it occurred mainly in the wet monsoon season it was known as "season cracking"

 

[Carburize]

Should have given you the reference to the above information.

"Corrosion and Corrosion Control"
by H.H.Uhlig