Stress corrosion cracking in brass

[Blueberg]

Hi guys, I have a set of natural gas powered generator sets using Cummins QSK60 engines. We have suffered radiator core (brass tubes + copper header plates) failures after only 4000 hours of running, on analysis we discovered the failures were due to stress corrosion cracking.

There are three components that can contribute to SCC, high stress, a material susceptible to SCC and ammonia. We did some laboratory work and seen that ammonia was present, low values around 15-20 ppm.

The coolant we are using contains nitrite, I have heard that this can breakdown to form ammonia.

We are running trials using several new avenues, these being a material that is less susceptible to SSC, thicker tubes, system pressure reduction and coolant that is nitrite free, obviously these trials will be done using singular changes so we can evaluate what change has hopefully worked.

Couple of questions, has anyone had experience of ammonia in coolant? Where did the ammonia come from?

Is there any additive we can add to the coolant to counteract the ammonia and prolong the life of our cooling system as a interim countermeasure?

All comments, advice or questions welcome.

 

[metengr]

The one good thing associated with stress corrosion cracking is if you can eliminate only one of the three contributors (as mentioned above) the mechanism will cease.

 

[EdStainless]

You can't change the temp and you can't get the stress low enough.
You will either need to move to a coolant that is free from possible sources of ammonia or you will need a brass that is more resistant.
Normal coolant additives have inhibitors in them that prevent the formation of ammonia.
Sounds like you need a new coolant source.

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Plymouth Tube

 

[Metaljon]

Traces of ammonia in the environment are an important agent in inducing SCC. Ammonia has a specific and selected action on the grain boundaries. Susceptibility to SCC in brasses diminishes with increased copper content. I would advise to change to a different copper alloy. The copper alloys that are virtually immune to SCC under normal service environment when exposed to ammonia are: C1100, C15100, C19400, C65400, C70600, C71500 and C72200.

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