Detecting non-visible defects in machined brass - Where to start?

ScottK

Not out of the crisis
Staff member
Super Moderator
#1
OK - I'm totally new to nondestructive testing so I'm looking for a starting point here.

Here's the situation - we've seen a significant increase in subsurface defects in half hard C36000 Brass rod. We've run across more inclusions during machining in the last two months than the owner has seen in 14 years.
To make matters worse, it's all of our suppliers. It's not narrowed down to a single supplier/heat/batch/whatever.
And some of our parts are for use in pretty high pressure applications.
None of our suppliers are being very supportive other than giving us our money back for the bad lots.
Needless to say we're terrified of the liability the failure of a high pressure valve could bring

So I've been tasked with researching testing alternatives -
Buy equipment? What kind?
Find a test lab?
Can you test machined brass parts for non-visible cracks, gaps, inclusions, etc?

TIA for any advice
 
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errhine

Involved - Posts
#2
Re: detecting non-visible defects in machined brass... where to start?

Any reason you couldn't do non destructive testing with ultrasound? There are many NDT methods used in aerospace, that are available, I dont see why they can't be used in other industries.
 

Cari Spears

Super Moderator
Staff member
Super Moderator
#3
Re: detecting non-visible defects in machined brass... where to start?

Have you sent any of the material to a metallurgical lab for independent testing?
 

ScottK

Not out of the crisis
Staff member
Super Moderator
#4
Re: detecting non-visible defects in machined brass... where to start?

errhine - I've just got a call from a guy that sells ultrasonic testing equipment - so I guess that's avenue 1.

Cari - No, we have not. Are there any labs you might recommend?

thanks!
 
A

antho10359

#5
Re: detecting non-visible defects in machined brass... where to start?

Since this problem is across multiple lots and multiple suppliers ... the only common denominator is the process. Have your storage facilities changed. (Too Hot or Cold) Have any process changes been made or personnel changed. Does the problem come and go ... happen on only one shift... Just a thought
 
T

True Position

#7
Re: detecting non-visible defects in machined brass... where to start?

If they are non-visable but surface you could look at die penetrant.

If they are sub-surface your may be looking at ultrasonic. Why bother with radiographic if UT would do the job? Also, I dunno if Eddy Current would work, but that's another relatively quick inspection.

Here's my favorite web site on NDT, the community college level descriptions:

http://www.ndt-ed.org/EducationResources/CommunityCollege/communitycollege.htm

One thing with NDT, is most customers will want certified level two techs to perform all inspections. With UT, you need many hours of practice, if I recall it's approximately 2,000 hours for Lvl II plus a number of hours of training.

Good luck
 

SteelMaiden

Super Moderator
Super Moderator
#8
Re: detecting non-visible defects in machined brass... where to start?

Hawat said:
If they are non-visable but surface you could look at die penetrant.

If they are sub-surface your may be looking at ultrasonic. Why bother with radiographic if UT would do the job? Also, I dunno if Eddy Current would work, but that's another relatively quick inspection.

Here's my favorite web site on NDT, the community college level descriptions:

http://www.ndt-ed.org/EducationResources/CommunityCollege/communitycollege.htm

One thing with NDT, is most customers will want certified level two techs to perform all inspections. With UT, you need many hours of practice, if I recall it's approximately 2,000 hours for Lvl II plus a number of hours of training.

Good luck
You can set up eddy current to catch sub surface defects, but you have to have an "as produced" sample with a known defect to get the proper set-up. Might be easier to UT?
 

ScottK

Not out of the crisis
Staff member
Super Moderator
#9
Re: detecting non-visible defects in machined brass... where to start?

Hawat said:
If they are non-visable but surface you could look at die penetrant.

If they are sub-surface your may be looking at ultrasonic. Why bother with radiographic if UT would do the job? Also, I dunno if Eddy Current would work, but that's another relatively quick inspection.

Here's my favorite web site on NDT, the community college level descriptions:

http://www.ndt-ed.org/EducationResources/CommunityCollege/communitycollege.htm

One thing with NDT, is most customers will want certified level two techs to perform all inspections. With UT, you need many hours of practice, if I recall it's approximately 2,000 hours for Lvl II plus a number of hours of training.

Good luck
wow. that's a great resource... I can see how I'm going to spend my morning tomorrow.

:thanx:
 
K

Kevin H

#10
Re: detecting non-visible defects in machined brass... where to start?

I'm familiar with all the above suggested methods as they refer to steel - if your material was steel and the problem was non-metallic inclusions two methods come to mind - magnaflux (magnetic particle) testing, and destructive testing of a small sample by preparing a sample for metallographic analysis under a microscope to check inclusion levels. Once one is found, you might also want to have an SEM analysis to get a rough chemical composition to help detect the probable source.

Extrapolating to brass, my guess would be sampling incoming material and having someone do a metallographic analysis, and then rejecting/approving based on analytical results. I do not believe ultrasound, radiographic, or eddy current would detect an inclusion on a microscopic level. Either ultrasound or radiographic should be able to detect macro size defects.

Do you have any information as to size/chemical composition of the defects you're encountering?
 
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