16 replies to this topic

[GMO]

Our auditor wants to see on historical equipment that we have 316 stainless steel because that's the type of metal detection piece we use. What's your opinion on that?

What I'm getting at is if we have any 304 stainless on site (which is likely in all food sites) I think he would want us to test for both types of steel. Seems excessive to me.

Edited by GMO, 07 March 2012 - 08:28 AM.

[D-D]

I seem to remember hearing somewhere that they were going to be a bit more lenient on documentation for old equipment that would have been conceived before anyone even thought of a BRC standard.

As for which grade of SS to be detecting, I am no expert on that though I would have thought bits of SS are unlikely to fall off a large piece of machinery and it is more what the blades / nuts and bolts etc are made of (or anything else that could either loosen or chip and fall in).

[campbell]

Stainless steel is made in diofferent grades. these all have differing levels of chromium and ferrous metals present. Some grades allow magnets to stick or even go rusty. Therefore the test piece should be the same as the majority of equipment present so that the metal detector can be set up correctly. It is part of the HACCP validation process to ensure that the metal detector is working effectivly.

[GMO]

But is this realistic? We found evidence the metal he asked for is 316 stainless but is the detectability of 304 stainless really all that different? We have titanium on site too but we don't have a titanium test piece. We have metal detectable plastics but we don't have a metal detectable plastics test piece. My point is you can go too far...

[reyaquino]

Our auditor wants to see on historical equipment that we have 316 stainless steel because that's the type of metal detection piece we use. What's your opinion on that?

What I'm getting at is if we have any 304 stainless on site (which is likely in all food sites) I think he would want us to test for both types of steel. Seems excessive to me.

316 SS is of higher grade than 304 SS. In fact 304 is not advisable to use for food. If you can detect 316, there is no reason why you cannot detect 304.

[GMO]

316 SS is of higher grade than 304 SS. In fact 304 is not advisable to use for food. If you can detect 316, there is no reason why you cannot detect 304.

Do you have a reference for that?

Why is 304 not advisable for food? I've read it's ok.

[Jim E.]

316 grade stainless is considered the food grade because it survives better in a chloride environment. However, 304 is acceptable but replacement may end up being sooner than later. As for detectability if you are using a 316 SS wand on your equipment and it rejects any 304 that were to pass would also be rejected as it is more magnetic that 316.

My thoughts any ways.

[Charles.C]

Dear All,

Sort of UK-oriented food grade suitability response -

http://www.bssa.org.....php?article=45

Expanded US appraisal of sanitary requirements for food contact/non-contact surfaces -

http://edis.ifas.ufl.edu/fs119

I can think of other specialised factors which may practically dictate also, eg low temperature freezing belts.

Rgds / Charles.C

added - extracts below seem to respectively disagree (No.1) and agree (Nos 2,3,4) regarding the relative 304/316 response characteristics given in JimE's post (I assumed a "comma" after the word "rejects" ). The practical situation may apparently also relate to the source of any to-be-detected fragments since the specific magnetic permeabilities can depend on their fabrication history, (especially can increase for SS304, AFAI could see from the literature).

I suppose it would be interesting to compare the quantitative detector response for wands of each variety. Hopefully 304 will be consistently (and significantly) > 316. Bye-bye BRC ?

Or just add one more, possibly meaningless, validation job, with thks to BRC.

1. The most common types of metal contamination in a broad range of industries include ferrous (iron), copper, aluminum, lead and various types of stainless steel. Of these, ferrous metal is the easiest to detect and relatively simple metal detectors, or even magnetic separators, can perform this task well. Stainless steel alloys are extensively used, particularly in food processing equipment, and they are the most difficult to detect, especially the common non-magnetic grades such as 316 (SN58J) and 304L (EN58E). The non-ferrous metals such as copper and lead fall between these two extremes
…………..>>
Other factors that influence sensitivity include type and shape of metal, orientation, operating frequency and throughput speed. A good indication of a detector’s all-around capability is the sensitivity ratio between ferrous and the most difficult to detect grade of stainless steel 304L (EN58E). This ratio can be as good as 1:1½ and as poor as 1:2½. This has a major effect on the detectors ability to detect contamination such as slivers and screen wire which exhibits an “orientation effect.” Non-spherical metals such as wire are easier to detect when passing in one orientation as opposed to another.

 food metal detection and x-ray inspection (2006).pdf   84.56KB   120 downloads

and possibly opposing views -

2. Test your metal detectors at regular intervals, every hour is common practice, use three test samples made from Ferrous (Chrome Steel), Non-Ferrous (Brass) and grade 316 Stainless Steel. Grade 316 Stainless is used as it has Non-Magnetic properties, which means that it is one of the most difficult grades of Stainless Steel for a metal detector to find. So the theory is, if it can find this grade then it will certainly find the others

(note that "others" does not explicitly include SS304, I noted the company does also offer test spheres for 304)
http://www.fastecser...test-standards/

3. Stainless Steel 316 has slightly better corrosion resistance than 302 and 304. It also has better non-magnetic properties

http://www.alloywire.com/alloy_stainless_steel_316.html

4. A noteworthy difference between 304L and 316L stainless steel is that while 304L is “low magnetic”, 316L approaches non-magnetic in character.
(The “L” parameter indicates that the material is “low carbon” steel (less than 0.03%). Low carbon improves ability to resist corrosion, particularly in salt environments.)

http://vandalstop.com/index.php?main_page=page&id=4

[reyaquino]

Do you have a reference for that?

Why is 304 not advisable for food? I've read it's ok.

304 is basically acceptable for food. However it easily deteriorate (corrode) in chloride, acidic, and alkaline environment compared to 316 which practically does not. So if you are processing acidified food in 304, you would not know if corrosion has started setting in and adulterates your food.

[ScottN_AMQA]

But is this realistic? We found evidence the metal he asked for is 316 stainless but is the detectability of 304 stainless really all that different? We have titanium on site too but we don't have a titanium test piece. We have metal detectable plastics but we don't have a metal detectable plastics test piece. My point is you can go too far...

True you can go too far, but how many surfaces and pieces fo equipment use titanium or metal detectable plastics ? if they are uncommon or not directly in the product flow or where common metal to metal surfaces are I think you could justify that you don't test them.

[jess.g]

Hi Charles,

 

Did you ever uncover any scientific justification of testing just one type of stainless steel? 

We currently supply 2 companies - one requires SS304, the other SS316. 

My current understanding is that if the x-ray machine is capable of detecting 316 then it can definitely detect 304 - however I feel "my understanding" may not be good enough for the auditors.

I have reached out to both our x-ray supplier and our test wands supplier already but when I came across this thread I felt compelled to ask.

 

Worst case scenario we will conduct our own challenge and use that as the justification. 

[Charles.C]

Hi Charles,

 

Did you ever uncover any scientific justification of testing just one type of stainless steel? 

We currently supply 2 companies - one requires SS304, the other SS316. 

My current understanding is that if the x-ray machine is capable of detecting 316 then it can definitely detect 304 - however I feel "my understanding" may not be good enough for the auditors.

I have reached out to both our x-ray supplier and our test wands supplier already but when I came across this thread I felt compelled to ask.

 

Worst case scenario we will conduct our own challenge and use that as the justification.

 

Hi jess,

 

previous posts related to metal detectors.

 

Is yr above query regarding metal detector or x-ray ?

 

The sensitivity logic is different.

[GMO]

Hi Charles,

 

Did you ever uncover any scientific justification of testing just one type of stainless steel? 

We currently supply 2 companies - one requires SS304, the other SS316. 

My current understanding is that if the x-ray machine is capable of detecting 316 then it can definitely detect 304 - however I feel "my understanding" may not be good enough for the auditors.

I have reached out to both our x-ray supplier and our test wands supplier already but when I came across this thread I felt compelled to ask.

 

Worst case scenario we will conduct our own challenge and use that as the justification. 

 

X-rays work differently to metal detectors.  X-rays work by detecting density not by the disturbance in a magnetic field.  The density of the two grades of stainless will not be significantly different to cause an issue with x-ray detection but the argument was that 304 and 316 cause different field effects in a metal detector. 

 

So for an x-ray, I really wouldn't worry.  For metal detection, I've now asked a few auditors and looked around and it appears that 304 is easier to detect in a metal detector than 316 so 316 is always the best one to use.

 

One thing to be careful with for x-rays though is you must use the right test pieces.  You can't use the hard plastic metal detector sticks you use in normal metal detectors as it's possible for the x-ray to pick up the hard plastic.  Then your, say, 4mm test piece is actually a 5cm test piece!  You should use specific x-ray test pieces or test cards.

[Charles.C]

X-rays work differently to metal detectors.  X-rays work by detecting density not by the disturbance in a magnetic field.  The density of the two grades of stainless will not be significantly different to cause an issue with x-ray detection but the argument was that 304 and 316 cause different field effects in a metal detector. 

 

So for an x-ray, I really wouldn't worry.  For metal detection, I've now asked a few auditors and looked around and it appears that 304 is easier to detect in a metal detector than 316 so 316 is always the best one to use.

 

One thing to be careful with for x-rays though is you must use the right test pieces.  You can't use the hard plastic metal detector sticks you use in normal metal detectors as it's possible for the x-ray to pick up the hard plastic.  Then your, say, 4mm test piece is actually a 5cm test piece!  You should use specific x-ray test pieces or test cards.

 

Yes. In fact the density of 304/316 is identically quoted in google.

In fact, as I understand, x-ray is recommended for SS rather than MD.

But the cost is another matter, especially, apparently, regarding spare parts/service.

[jess.g]

One thing to be careful with for x-rays though is you must use the right test pieces.  You can't use the hard plastic metal detector sticks you use in normal metal detectors as it's possible for the x-ray to pick up the hard plastic.  Then your, say, 4mm test piece is actually a 5cm test piece!  You should use specific x-ray test pieces or test cards.

 

Thanks so much for your reply! We currently use x-ray but have a "back up" metal detector. Fortunately my boss is a bit of a tech-head so the x-ray machines really appealed to him.

We did have one serviced last year that needed a generator replaced - it was a second hand refurbished generator but the price still blew me out of the water!

We currently use test cards for them but found that the test wands plastic was not dense enough to be picked up. Our machine highlights on  the display screen what caused the rejection and highlights the area so we before we moved to the cards we used that to verify that the wands were rejecting for the test material and not the wands themselves :) 

 

Thanks again!

[Charles.C]

Hi jess,

 

I conclude that yr original query (Post11) was unrelated to the rest of the thread.

[FurFarmandFork]

As part of your validation documentation, it sounds like your xray or MD manufacturer should weigh in on whether one type will be "easier" to detect than the other, then you can just use the harder one for your validation/verification activities. Hard for an auditor to argue with the manufacturer unless they have additional expertise.