stress relieving brass 2

[andimat]

In summary, a C37700 alloy threaded plumbing component failed in service due to definite evidence of a combination of SCC and dezincification. Metallurgical examination did not indicate any abnormalities in the microstructure; it was characteristic for free machining α-β brass, forged and cold-worked (drawn). I would appreciate any comments on how one can determine if the brass component was stress-relieved since this procedure it is usually done at a temperature below the recrystallization temperature and as such, it has little or no effect on the microstructure.

 

[metengr]

Why are you concerned about stress relieving brass? Obviously, the wrong material was selected for this environment based on the confirmed damage mechanisms, especially dezincification.

 

[EdStainless]

If you have dezincification then the water is aggressive to this alloy and you need a better grade of brass. period.

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Plymouth Tube

 

[Metaljon]

A common problem with these plumbing alloys is that the composition is out of specification to the International Standards. Lot of these fittings are manufactured in China with very poor quality control systems. Usually brass has additive of arsenic 0.02 to 0.25% and provides protection against corrosion dezincfication. This is commonly referred to as Dezincfication Resistant Brass (DZR). Check the composition of the alloy against the C37700 specification. If the composition is out of specification then that will be the primary reason why dezincification and SCC has occurred. Impurities of iron, manganese and nickel are suspected to also to influence SCC occurrence in brass. Recommendations in the latest guidelines are to use DZR brass with iron contents below 0.1%. SCC in brass alloys is influenced by many factors including: Water quality; Alloy composition and microstructure; Manufacture Processing (heat treatment, machining); Geometry of the finished product and contact with other metals.

The stress relieving temperature for C37700 is 500F or 260C. The recystallisation temperature of copper alloys is influence by cold working, so a temperature of 260 C is almost certainly going to cause structural changes in the alloy. Do a hardness survey on a cross section and if there is a lot of variation in hardness it will almost certainly not been stress relieved after machining. It is common practice in China not to do stress relieving treatment on plumbing fittings after machining as the alloy is normally supplied in bar which have been stress relieved and the Chinese believe that no further treatment after machining is necessary. They is a famous quote by Confucius. "The people may be made to follow a path of action, but they may not be made to understand it".

 

[andimat]

Thanks guys for the comments. For the purpose of my application, Metaljon's suggestion makes sense. I appreciate your input Metaljon.

 

[stanweld]

Unfortunately, almost all copper based plumbing components readily available in the USA are made in China.