Brass Fitting Failures
Brass Fitting Failures
(OP)
I'll apologize for the very long post, but I've been working on this failure for a few months now and have gathered a lot of data.
We are experiencing a large amount of brass fitting failures as of late. These fittings have been in service since the 1980s and have been C 36000 brass from the very beginning.
The recent failures are intergranular in nature. The material meets requirements for C 36000 chemistry. The hardness is in the typical range for the material.
The failures have been coming from trucks that have been in outdoor storage for close to one year. The interesting thing to note is that there have been hundreds of trucks in the same storage location but only a random sampling of the fittings are failing (which leads me to believe that environment is not the root cause of failure). We also have fittings that have been in the field for 10-15 years that have not experienced cracking. We don't believe the fittings are being over-torqued as we have torqued some fittings to 3 times the print max and ended up stripping threads prior to replicating the failure.
Because we have had success with the material for years I have been trying to collect data comparing
1. Failed fittings from 2008-2009 time period
2. Non-failed fittings from 2008-2009 time period
3. Non-Failed fittings from the 1995 time period
So far I've only identified two main differences, beta phase presence and distribution and lead distribution.
I've now been trying to broaden my knowledge of brass. I've learned that the beta phase is often present in leaded free cutting brass and the percentage of beta phase increases with higher zinc content. I've also learned that the beta phase is harder, stronger and more brittle than the alpha phase. I'm seeing the beta phase in a network or conglomerate in the sample, not randomly dispersed, so I'm not sure how to measure the percentage of beta phase present.
I'm seeing the lead present on the grain boundaries, which I believe is typical. But the failed fittings have a different lead distribution when compared to the non-failed fittings.
Can anyone provide insight on how the beta phase or lead distribution affects the strength of the brass?
Also, if anyone has other suggestions for possible failure modes; I'm all ears. I've attached some micrographs of the fittings.
We are experiencing a large amount of brass fitting failures as of late. These fittings have been in service since the 1980s and have been C 36000 brass from the very beginning.
The recent failures are intergranular in nature. The material meets requirements for C 36000 chemistry. The hardness is in the typical range for the material.
The failures have been coming from trucks that have been in outdoor storage for close to one year. The interesting thing to note is that there have been hundreds of trucks in the same storage location but only a random sampling of the fittings are failing (which leads me to believe that environment is not the root cause of failure). We also have fittings that have been in the field for 10-15 years that have not experienced cracking. We don't believe the fittings are being over-torqued as we have torqued some fittings to 3 times the print max and ended up stripping threads prior to replicating the failure.
Because we have had success with the material for years I have been trying to collect data comparing
1. Failed fittings from 2008-2009 time period
2. Non-failed fittings from 2008-2009 time period
3. Non-Failed fittings from the 1995 time period
So far I've only identified two main differences, beta phase presence and distribution and lead distribution.
I've now been trying to broaden my knowledge of brass. I've learned that the beta phase is often present in leaded free cutting brass and the percentage of beta phase increases with higher zinc content. I've also learned that the beta phase is harder, stronger and more brittle than the alpha phase. I'm seeing the beta phase in a network or conglomerate in the sample, not randomly dispersed, so I'm not sure how to measure the percentage of beta phase present.
I'm seeing the lead present on the grain boundaries, which I believe is typical. But the failed fittings have a different lead distribution when compared to the non-failed fittings.
Can anyone provide insight on how the beta phase or lead distribution affects the strength of the brass?
Also, if anyone has other suggestions for possible failure modes; I'm all ears. I've attached some micrographs of the fittings.





RE: Brass Fitting Failures
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RE: Brass Fitting Failures
RE: Brass Fitting Failures
I'll look more closely at the grain boundaries in the SEM.
Thank you!
RE: Brass Fitting Failures
Keep looking for chemical contaminants in the cracked ones.
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Plymouth Tube
RE: Brass Fitting Failures
RE: Brass Fitting Failures
My initial look at the microstructure images did not lead me to conclude that the beta phase amount & distribution were the proverbial smoking gun, but I am not a brass expert, so I won't take it personally if you choose to discount that statement. I would have some residual stress measurements made using x-ray diffraction before I would focus solely on the microstructure. Proto in Ontario, TEC in Tennessee, and Lambda in Ohio are all very capable companies that could provide this type of service.
RE: Brass Fitting Failures
Please see file for updated images.
Thanks!