SS304L / SS316L - how to check on them ? 7

[azertyuiop]

Dear collegues ,

I want to check if the contractor is supplying my company an installation with the much more expensive SS316L materials that was demanded , and make sure he doesn't supply us cheaper SS304L materials instead (pharma applications).

How to check on this without damaging the delivered equipment/piping networks?

I have already used magnets to check if we are dealing here with stainless steel (the magnet doesn't clinch = SS) , but how to differentiate between the SS304L and SS316L variety ? Some tubing has SS316L inkinscriptions , but most (polished) parts are not tagged.

Expert advise needed.

regards.

 

[unclesyd]

On the material not coded the only sure way is by chemical analysis. This can be done by having a company that does PMI come in and verify the materials. This is a very expensive proposition at any time especially post fabrication.

Differentiation between 304 S/S or 316 S/S is no problem, it’s the Carbon analysis that differentiates between the low carbon forms of these metals. The carbon analysis doesn’t lend itself to field work or to fabricated parts.

You can request MTRs of all the material used in the project. By doing this you are depending on the integrity of the fabricator of which you seem to have doubts. It gets a little sticky but you can ask for a certificate of compliance on the materials supplied. Not absolute, but closer to a resolution of you problem. It sounds nasty but if you find one non-compliance component you have some leverage to have him prove that he used the correct materials.

It isn’t a very good practice to start inspection in the middle of the game. These type problems are easily avoided with onsite inspection or preapproval of a fabricator. There are other ways and means to assure that fabricator is complying with specifications. This gets pretty involved but I would get with your AI and discuss with him the different ways to handle this. You can use a third party inspector at the fabricator if you don’t a have someone that has the experience to carry this out.

I can’t say it enough that situations like this are avoided best by up front work on a project.

 

[quark]

It is easy to check whether a given steel is 316 or 304 by doing Mo test. Ready made kits are available in the market and the test takes a minute time. But this will not differentiate your steel from any other Mo steels. I would actually follow Unclesyd's comments. To check whether it is L or not , only option is to for a chemical analysis.

It's a requirement(this should include in your equipment qualification) in pharma industry to get the piping material chemical tested if it is used for high purity application. We generally ask the suppliers to get that done and we also send one sample to the test labs.

Regards,


Believe it or not : Eratosthenes, a 3rd century BC true philologist, calculated circumference of earth with the help of a stick and it's shadow. The error was just 4% to the present day calcuated value.

 

[unclesyd]

Thinking a little further on your problem. If your main concern is the differentiation of the 304L vs the 316L material and not considering the L component there are spot tests that will different between the two based on the Molybdenum content of the 316 S/S.
There are commercial kits available to do this, but being a pharmaceutical manufacturer you should be able to come up with a old standby.

Use a 50/50 v/v conc HCl and water saturated with SO2. Clean a spot on the subject piece add a couple of drops of the solution and allow ten seconds rinse and look for a purple tint. Always use a standard piece of 316 S/S to compare. The solution has to be regenerated often. We used small cans of SO2, like the old freon cans, to make the solution. There was a recent post that named providers of the spot test kits. Remember all you need is the Moly test. Thinking a little further on your problem.

If you are near a big metal recycling firm and they have a portable X-ray for metal identification you might have them verify a few pieces of piping prior to getting a PMI group involved. Not binding but could give you piece of mind.

Go to thread 723-39689 Look at “Rich2001's Post. The Koslow kits are the one’s we used on different elements.

 

[moltenmetal]

Careful with the spot tests for Mo- much 304 these days is made using mixed SS scrap, and so it can have some Mo content- enough to possibly fool the spot test, but not enough to meet the 316SS spec.

If 316 vs 304 is very important to you, it's best to use PMI. The x-ray fluorescense machines they use are non-destructive and can quantitate all the alloying metals- except for the carbon content, for which you'll need to do chemical analysis. That means removing a significant mass of "filings" of the fittings in question (a gram or so per analysis), so it's practical for larger pipe sizes only- don't even attempt this on tubing/tri-clamp fittings (such as commonly used on pharma applications) because you'll end up affecting the wall thickness.

Better still, use a fabricator that you trust and review the mill certs for the material. Back it up with the threat of random PMI examination, and a reputable manufacturer shouldn't cause you too much trouble. And spec 316/316L dual stamped material- these days, it can be had at virtually no difference in cost and meets both specs.