304 or 316 Stainless Steel 1

[ozfish]

I was curious as to a method (simple if possible) that can test for 316 as apposed to 304 stainless steel.

A test that possibly could be done on-site would be the most advantageous.

Thanks

 

[metengr]

There are portable, x-ray fluorescence alloy analyzers that are nondestructive, and can distinguish between 304 and 316 SS. If you only need to have a single analysis performed, you can have metallurgical lab personnel perform this activity on site. Some labs identify the material analysis as positive material identification (PMI).

 

[quark]

Molybdinum testers are used for this generally Which will only give you a clue. Better is to go for complete analysis.

 

[NickelMet]

Depending on what you want to spend or buy:

1) long term purchase - get a portable alloy analyzer (NITON, SpectroAnalytical, etc.) - be prepared to spend some money though (in excess of $30,000 usually) - reason to purchase is frequent checks, fast results.

2) short term purchase - alloy spot checking kit (wet chemistry) - inexpensive, usually under $1000 - reason to purchase is infrequent checks, budget prohibits larger purchase.

3) no purchase - hire a metallurgical or NDE analysis company to provide the service on a contractural or per need basis.

We use a NITON II (portable, handheld, looks like a phaser from Star Trek) where I work. It has been fairly reliable and provides a good quick analysis (from power up to results usually in less than 2 or 3 minutes). The only drawback is distinguishing between the same type of metal that has differing carbon or sulfur contents.

~NiM

 

[Rich2001]

According to ASTM STP 550 "Nondestructive Rapid identification of Metals and Alloys by Spot Tests," available from the ASTM,

http://www.astm.org

(limited supply available) the test for molybdenum in 300 series stainless is to

a) Place equal drops of concentrated hydrochloric acid and concentrated nitric acid on the metal surface. Allow 3 to 4 minutes for reaction and transfer 2 drops to a spot plate.

b) Add 2 drops of 10% potassion thiocyanate.

c) Add 25% sodium thiosulfate dropwise stirring until the red color begins to disappear. A violet color will appear if molybdenum is present.

However, you can purchase a chemical spot test kit form Koslow or Systems Scientific Labs.

 

[EdStainless]

The purchased spot test kits have some of the chemicals incorporated into strips of paper. You put the acid on the surface and then the paper. If the paper turns purple there is Mo present.
There is a simple electrochemical verison also that uses a battery and an electrolyte to drive the same reaction.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[ozfish]

Thank you all for you advice.
The purpose does not warrant the cost of equipment and the test kits are possibly the way to go - however I was hoping to do the test in the next day o r so at a plant that was being decommissioned.

I have found some information that suggests the use of Sulphuric Acid or HCL.

The Sulphuric acid on 304 - Strong attack - green crystals and dark surface

The HCL on 304 -Fast attack - gas formation

______________________________________________

The Sulphuric acid on 316 - Slow attack - tan surface turns brown

The HCL on 316 - Very slow attack

Any thoughts on this form of testing.


Regards

 

[metengr]

ozfish;
In your situation, I would call on a metallurgical lab and have the PMI performed on site using a portable alloy analyzer, as NickelMet stated in option 3 of his post. This can be done quickly, and probably for less than a couple hundered bucks (travel time for a tech).

 

[unclesyd]

Another old time spot test we used for years in a very critical service where 316 SS was an absolute requirement due to a corrosion rate of "0" vs 20" IPY for 304 SS.

Take a 50/50 HCl/Water, V/V, solution and saturate it with S02. The solution requires periodic re-saturating. Work outside or in a fume hood.


Slightly abrade the suspect material and a known and add one drop of the solution and let the reaction stop. Rinse in cold water and look form a purple color, molybdenum disulfide.
You may have to slightly tilt the test piece to see the color.
The only real interference is 303 SS where a black smut forms.