Metal Detector Testing When Used Only as X-Ray Backup

Good afternoon! Since I've worked here my company has always relied on an X-Ray machine for foreign material detection. We test this using three test wands (FE, Non-FE, SS) throughout the production day. However, we recently purchased a metal detector to add in-line as a backup plan in case the X-Ray machine goes down. I know that the metal detector needs to be added to our procedures/risk assessments, etc. However, since we only plan to use it when the X-Ray machine isn't working, it doesn't need to be check every day, only the days we use it right? And when testing, can we use the same test wands that we use for the X-Ray or do they need to be different? Any guidance is appreciated. Thank you in advance!

Only if your metal detector can do or exceed what x ray machine is currently doing, as per your operational procedure. 

I am not sure what you mean by it doesn't need to be checked everyday. What doesn't need to be?

Only if your metal detector can do or exceed what x ray machine is currently doing, as per your operational procedure. 

 

I am not sure what you mean by it doesn't need to be checked everyday. What doesn't need to be?

To make sure that it's working properly, such as running the test wands through it. 

I'd say you can check it only when you use it, as long as it is annually calibrated and verified for performance per its manufacturer's guidance. I don't see why you can't use the same test wands. Everything should be documented in your SOP/risk analysis. 

One question I'd raise is are your test wands specifically designed for x-rays?  The reason I ask is because some metal detection ones are designed with plastics which on certain settings (and depending on your product) may be x-ray visible.  I've normally seen test cards used instead which have thinner, flexible plastic.

Ones like this kind of thing:

Laminated X-Ray Test Card | Card for X-Ray Detector | Detectamet

So if you're using wands, I'd see no problem with using them for a metal detector, the question I'd have is if you should be using them for the x-ray.  Your technician could help advise.  It really might not be a problem for your product but certainly in the past (over a decade ago) I saw a test wand where the whole wand was visible to the x-ray on the settings they were using basically meaning they weren't checking for, say, 2mm but their test was showing them they could pick up a 50mm piece of hard plastic instead.  Great but not what the test was designed for.

We have a variety of devices and use the same pool of test pieces for them all under normal circumstances.  Most "non-ferrous" tend to be brass so this will probably be fine, as long as your instruments have the same lower threshold for sensitivity and you validate it.

We also have "extra" devices that can be used as backups or for processes that aren't done frequently.  Like our offline "rework" units.  These are given the annual checks, but only receive monitoring/verification testing when they are being used. Making sure to include a before and after is the only extra consideration, when compared to the units that are operating nearly 24/7.

Not sure why the company would not get another X-ray system as the backup as a metal detector may not detect everything that an X-ray machine would.

With that said, I have seen backup metal detectors go out of calibration when shut down for long periods of time - but of course that would be picked up once a start up is done and can then be adjusted.

Hi FSQAManager2025,

It would make sense to use the same three test wands (FE, Non-FE, SS), that way you confirm you are running the metal detector to the same specification of metal detection and removal as normal.

I would only normally test when in use but think it probably should be checked periodically if out of operation for a significant amount of time.

Kind regards,

Tony

Not sure why the company would not get another X-ray system as the backup as a metal detector may not detect everything that an X-ray machine would.

This was actually my first thought.   If your entire system is built around x-ray, and your HA and all that says you x-ray to be able to find certain foreign materials that a MD won't find, how's that ok?   Would an auditor accept that?

This was actually my first thought.   If your entire system is built around x-ray, and your HA and all that says you x-ray to be able to find certain foreign materials that a MD won't find, how's that ok?   Would an auditor accept that?

Depends what you're checking for and why.

X-rays can be hit and miss on different materials.  Ironically they can be really good at picking up the plastic in metal detector test sticks as I said above which is why I'd recommend cards but not so good at picking up the types of plastic we tend to use in production.

A lot of sites I've been to only validate and monitor for metal with x-rays.

If you're able to achieve the same sensitivity with a metal detector, theoretically there is no reason not to use that instead.  The technology is different but it's still valid.  Problem will be is you're unlikely to be able to get the same sensitivity.

X-rays and metal detectors are different in lots of ways though and detect differently.

X-rays

Detect by density

Good at detecting stainless steel in products

Tend to be more sensitive

Bad at detecting aluminium

Moderate at detecting metal detectable products (you must check they are detectable)

Can get false positives for bones (which might be advantageous if it's a defect but not if you're making something intentionally with bone in)

Can detect other contaminants but proving it is a ball ache

Should use test pieces specifically for x-rays to avoid detecting the stick not just the ballbearing

Expensive

Metal detectors

Detect by magnetic field disturbance

Sensitivity is highly product dependent

Product signals where there is a lot of water tend to be high

Tends to be least sensitive for stainless steel which is the most used metal in food manufacturing

Bad at detecting aluminium

Good at detecting metal detectable products

Can detect multiple small contaminants in one pack even if only one wouldn't have been enough to trigger on its own

Can be bad at detecting thin wires (orientation effects)

Can't detect other contaminants

Cheaper depending on what other bells and whistles you have

Depends what you're checking for and why.

 

X-rays can be hit and miss on different materials.  Ironically they can be really good at picking up the plastic in metal detector test sticks as I said above which is why I'd recommend cards but not so good at picking up the types of plastic we tend to use in production.

A lot of sites I've been to only validate and monitor for metal with x-rays.

 

If you're able to achieve the same sensitivity with a metal detector, theoretically there is no reason not to use that instead.  The technology is different but it's still valid.  Problem will be is you're unlikely to be able to get the same sensitivity.

 

X-rays and metal detectors are different in lots of ways though and detect differently.

 

X-rays

 

Detect by density

Good at detecting stainless steel in products

Tend to be more sensitive

Bad at detecting aluminium

Moderate at detecting metal detectable products (you must check they are detectable)

Can get false positives for bones (which might be advantageous if it's a defect but not if you're making something intentionally with bone in)

Can detect other contaminants but proving it is a ball ache

Should use test pieces specifically for x-rays to avoid detecting the stick not just the ballbearing

Expensive

 

Metal detectors

 

Detect by magnetic field disturbance

Sensitivity is highly product dependent

Product signals where there is a lot of water tend to be high

Tends to be least sensitive for stainless steel which is the most used metal in food manufacturing

Bad at detecting aluminium

Good at detecting metal detectable products

Can detect multiple small contaminants in one pack even if only one wouldn't have been enough to trigger on its own

Can be bad at detecting thin wires (orientation effects)

Can't detect other contaminants

Cheaper depending on what other bells and whistles you have

Yeah, that's exactly my point, they're different.   If your foreign material risk analysis is built around an x-ray that detects plastics and all kinds of other things, then a metal detector cannot take its place, no?    If so, what's your control on foreign material other than metal?

If you're handling your foreign materials other than metal in other ways, you're covered.   IF not, your slip is going to showing, as the saying goes....

Yeah, that's exactly my point, they're different.   If your foreign material risk analysis is built around an x-ray that detects plastics and all kinds of other things, then a metal detector cannot take its place, no?    If so, what's your control on foreign material other than metal?

If you're handling your foreign materials other than metal in other ways, you're covered.   IF not, your slip is going to showing, as the saying goes....

My point was that x-rays are not, in my experience, very reliable at detecting things like plastic.  So even if you have an x-ray, you will need other controls for plastic.  So yes, if a metal detector detected metal at the same sensitivity as your x-ray (that's a big if) then I would feel comfortable to defend that because most test pieces for other contaminants are not actually the ones you have in your factory.  E.g. glass test pieces are often soda glass.  Plastic is the wrong density so the test piece detects but a piece of your plastic tubs wouldn't.  Etc. etc.  I know of few x-ray systems I've come across where they're using it for something other than metal.  Where they are, when you probe, it tends to fall to pieces under scrutiny when you look at the material specs vs. their test pieces or they're using something which will detect raw bones but not cooked ones (that's a classic).

But anyway, this is a bit off topic.  The question was on test pieces and if the same "wands" could be used in a metal detector.  To my mind, the word "wands" makes me think the wrong test pieces might be in use for an x-ray anyway though as metal detector wands are not necessarily the correct test items for x-ray and the x-ray test pieces tend to be flexible cards.  I can't be the only person who has come across this?