Here is another view.

• https://files.engineering.com/getfile.aspx?folder=d483586b-d4c1-4163-aa9c-1

That looks like brass plated over something else.

no its a brass casting fracture surface is shiny.

Sorry - I don't have the parts and have to depend on your photos.

Best advice - buy from a reputable source.

One of two thoughts. Either cracks that started in the casting process (these should have some slight discoloration) or threading tools that are too sharp (not enough root radius). Of course the walls could just be too thin by someone trying to cheat and save metal.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

hercules
send it to a met lab for failure analyses, my guess bad product. defects

Happened 3 times? Three nipples tried into the same mating hole, or three nipples tried into three different mating holes?

What is the thread form supposed to be? Is it actually?

Same questions for the mating hole or holes?

How big is the gorilla doing the assembly and how long is his wrench? It's brass. Brass is not a particularly strong metal. Twist it hard enough and it will break.

Do not waste your money on a lab failure analysis because you will get no useful actionable information.

If the lab reports that "it's bad", what do you do with that report? Demand a refund? Take it to the supplier and wave it their face demanding process improvements?

This is commodity junk from China or India. How much time and expense are you going to spend on it?

Rule out any obvious problems with the thread forms and assembly process, then get on with life. Order new nipples from a different supplier if you don't find any obvious problems.

I don't think material defect would cause such consistent failures. The inside bore is too large, you have nearly zero thickness at the minor diameter of the thread.

Considering the form of the break, it looks like they were installed and then they were side loaded until they broke.

One of them looks to have an o-ring groove on the end, but man that is some awful and incomplete photography - like where are the broken off fragments, where were they installed? In the first picture - is that a long prying lever threaded into the broken piece?

First off one makes a fish bone of all possibilities. What caused the failure. One coming to to a conclusion what caused is not the way to solve this. One has to eliminate what it is not.and what it is. It could be dimensional, parent material defects, or bad design. Even looking at the assembly procedure
Torque values,

Thank you all. Good tips, I will look into dimensional as material didn't reveal anything.

Next time, please invest in a better camera; better photos = better interpretations.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

Hi Hercules28

It looks to me like an overload failure ie the tensile load put on the threads while tightening up was to high.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

Agree with desert fox - this is consistent with overload on tightening. The real question is why this overloaded, and you do not have sufficient information to provide this answer (i.e. was it overtorqued? casting defects? machining issues? etc.) You will probably need deeper examination from a met lab.