Stainless steel screw and bolt material acceptance testing

[QualityJoe]

Does anyone know or can guide me to a source that has a good procedure/practice for acceptance testing of stainless steel scews and bolts?
I am trying to develop an incoming inspection to ensure we recieve good guality corrosive resistant stainless steel hardware. Need to find a quick spot check method to use to inspect lots recieved. Is using a magnet to check for ferrous contamination in stainless steel a good test method?

Please advise

 

[unclesyd]

What grade SS are you using as it makes a difference on how to test the fasteners?

A magnet is not 100% effective as many screws are cold worked and will be moderately magnetic. If you test a SS fastener and its shows some magnetic properties you have to heat a sample to cherry red and air cool. If it's SS it will show no magnetic properties.

 

[SJones]

Try a search on 'positive materials identification' and look at EEMUA 149

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[QualityJoe]

Most are 18-8 SS, however I have seen 304 SS recieved with some attraction to magnets.
I will have to try the heat test you mentioned to prove that out..

Thanks.

 

[unclesyd]

18-8 cover a broad range of materials so the best way is just to verify that all are stainless.
In addition to the magnetic test if you have the facilities and are familiar with handling acids you can use a 50/50 v/v solution of Nitric Acid.

Are you familiar with using acids?

 

[QualityJoe]

No, not really. Just with citric acids for SS passivation purposes.
I really dont want to open up another hazmat waste profile just for testing hardware, cost and man hours alone will be inefficient for me right now..

I have instructed purchasing dept to have certificates of compliance from the vendor of the hardware batch lots sent, hoping to put the ownership on the vendor, but I still need some quick test method for in house.

 

[unclesyd]

I don't know your application but just generally as stated above 18-8 covers a lot of materials. So if you are just looking for a pretty fastener I think the magnet test will eliminate the majority of the impostors.

 

[QualityJoe]

we build interactive aqauitic playground systems and fountains which require stainless steel fastners to secure and install water elements. We have had many site repair visits and found that we have had items fail due to the fastners rusting out within a years time frame, or less some times.
I am not too concerned on how pretty it may look but rather its resistance to corrosion to help reduce and possibily elimnate the amount of warranty repairs performed through out the year.
For now I have my inspectors using magnets to inspect incoming material and have seen these past few days a large amount of 18-8 fastners are attracted to magnets.

Is this normal with 18-8?

 

[unclesyd]

If the fastener is made by cold rolling this is a fairly common occurrence. You can use the heat test to verify that the base metal is SS.

What is the country of origin for the current fasteners? I ask this because all sorts of alloys are being used according to my buddy in the fastener business.

Ideally if corrosion or failure is a big concern you would specify a specific alloy like 304 SS or better yet 316 SS. Another approach would be to require domestic if in the US. Slightly higher but someone has to put their name on the box.

I have to admit that most anything labeled 18/8 should last longer than a year.

 

[QualityJoe]

Thanks for the tips..
I had my techs do a heat test on various fastners we have in stock. Most has some significant amount of attraction to magnets.
After the heat test this attraction to magnetism was still present but not as strong as before. thus was able to develop an inspection criteria.

I have implemented an AQL sampling on all fastners to be checked with magnets first and pass those with less magnetic attraction and perform heat test on those that have stronger attraction to magnet.
This I am sure will help monitor incoming material and keep the vendors honest...

Thanks again

 

[unclesyd]

Tell the techs to increase there heat probably about 100F and they should have no residual magnetism upon cooling. They only have to stay at temperature a half second or so.

 

[johnSchwaner]

I tried the "heat test" on some stainless aircraft "AN" bolts and a magnet is still attracted to them. Three tests on 3 different sizes all are still attracted to a magnet.

So are my stainless AN bolts bogus?

 

[unclesyd]

johnSchwaner,
No your bolts are probably not bogus as there are numerous Stainless Steels that are fully magnetic in all forms all the time especially the higher strength ones.

The heat test is specific for checking "Austenitic Stainless Steel" which are normally none magnetic except if they have been cold worked. 18-8 is a catch all term used to describe a family of Austenitic Stainless Steel fasteners.