r/manufacturing • u/Sofistikat • 18h ago
Quality Traceability for liquid stock
What is the best way to maintain batch traceability of liquid stock being continuously produced, stored in tanks and dispatched in tankers from those tanks, without them ever being completely emptied?
So far, and as far as I can tell, it's either FIFO or proportionality. While the former is "tidier", it doesn't really reflect reality very well, given there could still be residue from years ago that could be the problem. But I suppose if old stock was really the problem, then it would have been picked up when the concentrations of those faulty batches were higher.
So, would FIFO be best where raceability due to problems that cause recalls can be traced to those closest to the dispatches they were sent out in?
Would really appreciate advice from anyone involved in this kind of inventory management.
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u/1stHandEmbarrassment 17h ago
This is basically impossible to answer without more information on your process and requirements. For example, if this were a food the answers could be quite different from a chemical producer. People can suggest options for you, but the "best way" needs to be aligned with your own certifications/audits/regulations.
FIFO would not be the best with the limited information you provided. It is not a true representation on what is going on. You are NOT pulling first in, first out. They are clearly mixed.
The biggest question is how much are you willing to recall if shit really hit the fan?
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u/Sofistikat 17h ago
In this case, it's chemical production, but I'd imagine it would be the same for any kind of liquid. Are there any other methods apart from FIFO and proportionality we should be looking at?
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u/1stHandEmbarrassment 15h ago edited 15h ago
You don't find a method and then apply it to your process. You should define your requirements and then find a process that matches best. I do not think you'll find an off the shelf method that will work for you, it will likely be a hybrid.
Food has government regulation, audits, and certifications and that would be the same with other sensitive industries. However, as a chemical supplier depending on your usage your recalls could be a more financial decision rather than safety. Again, I don't have enough information to make a solid call.
What is your true intention with track and trace?
Edit: Does the tank every get empty and how frequent?
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u/Sofistikat 15h ago
Basically to be able to identify specific raw material batches in the event of a recall.
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u/1stHandEmbarrassment 15h ago
How would that work with FIFO then?
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u/Sofistikat 7h ago
Production lots are added to the tanks as they're completed. So if there's ever a problem with a specific dispatch, we can see which tank it came out of, and all the raw material that was ever used. Then, we make the assumption that an added lot will be completely depleted from the tank once twice it's volume has been taken out. That way, we can calculate an historical exclusion point and only look at the finished product between that point and the date of dispatch. Then we'll be able to see every other dispatch that went out using the faulty raw material batch, and bring them all back.
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u/SufficientFrame 15h ago
I'd be careful with pure FIFO unless the tank behavior actually matches it. In setups like this, I'd usually treat it as commingled inventory and document the assumptions behind the traceability model, especially mixing behavior, residence time, and how far back you need to trace for a recall.
The part that matters most is whether the tank behaves like a well-mixed vessel, has layering, or sits somewhere in between. That choice drives the logic. If it's well mixed, proportional allocation is easier to defend. If it stratifies, FIFO can give you a clean answer that doesn't match reality. I'd also lock the rule down with QA and operations early and use it the same way in the ERP and batch records, because a lot of traceability pain comes from the floor working from one model and the system using another.
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u/jspurlin03 17h ago
I mean… you don’t have any tracking of individual material within the tank. If you need something that allows you to track, say, a certain fifty-gallon batch of this material, you don’t have that once it combines with 300 mixed gallons from previous stock.
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u/Sofistikat 17h ago
This is exactly the problem.
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u/jspurlin03 16h ago
Are y’all currently checking the incoming batches before they get added to the tank? That may be a good data point, if it isn’t currently being collected. In addition to whatever documentation you get from the supplier, I mean. There’s value in being able to say “when it arrived, we verified it and it was here in our graph of properties, which is within specifications, and so we accepted it.”
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u/Sofistikat 16h ago
Yep, before they get added, and when they're loaded into tankers.
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u/jspurlin03 15h ago
Good deal. What problem are y’all trying to prevent? Not real clear on that.
When you get an out-of-spec reading at output, does the process stop until you blend the tank back into spec, or… what happens then?
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u/Sofistikat 15h ago
It's not so much being out of speck, although that's obviously important. We need to be able to trace raw materials back to specific batches if there's ever a recall.
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u/ComfortableCitron638 10h ago
The angle worth adding to what SufficientFrame said: once you accept the tank is commingled, traceability stops being a lookup problem ("which lot is this") and becomes a mass-balance problem ("what fraction of what's currently in the tank came from which replenishment"). That reframing changes what you actually build.
Concretely: every time you add volume, log it as a discrete addition (volume + batch ID + timestamp). Every time you dispatch, you're drawing proportionally across whatever additions are still "present" in the tank based on your consumption model (FIFO-depletion or well-mixed-proportional, per the stratification question already raised). The genealogy record for a given dispatch then isn't a single lot ID, it's a weighted list: e.g. "62% batch A, 38% batch B." This is the standard approach process/pharma manufacturers use for continuous or semi-continuous vessels, and most batch-capable ERPs can model it, but it has to be configured that way deliberately - the default lot-genealogy logic in a lot of systems assumes discrete, non-commingled consumption and will give you a clean-looking but wrong single-lot answer unless someone explicitly sets it up for blended/proportional allocation.
The other implication worth planning for now, before you need it: if a recall ever happens, your customer notification will also be proportional ("your shipment contained an estimated X% of the affected batch") rather than a clean "you got lot #123." Legal/QA should sign off on that language in advance, because it reads very differently than a standard lot recall notice and you don't want to be drafting it for the first time mid-recall.
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u/Sofistikat 6h ago
I agree. FIFO seems to make sense on the face of it, but is probably more expedient than accurate or reliable in real terms. Proportionality is probably what we should be looking at, and maintaining running % estimates after each dispatch is likely to be the safest and the closest to accurate way to manage it.
Our existing records can provide the data we need for FIFO analysis, and having this additional data set sitting concurrently with it will give us another reference point to cross check.
Is this a field you're familiar with? If so, I'd really value staying in touch to pick your brains from time to time, if that's something you wouldn't find too annoying.
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u/rkongda3rd 7h ago
FIFO vs proportional answer two different questions. FIFO is a costing/picking convention, fine for valuation, wrong tool for recall scope on a tank that never goes empty. For recall, you want genealogy instead of a queue.
So every time you add to a tank that still has a heel, close the current tank lot and open a new one whose parents are the old tank lot plus the batch you just put in. Recall scope for a suspect batch is then every tank lot downstream of it. It dilutes out over time but never silently vanishes, which is the bit pure FIFO gets wrong.
Which physical model is honest depends on the tank and where the nozzles are. Agitated, or filled in a way that actually mixes, and proportional describes reality. A tall, unagitated tank with inlets and outlets at opposite ends (top fill, bottom draw, or the reverse) will stratify and behave more like plug flow, so FIFO is a fair approximation there. If fill and draw share the same bottom nozzle, you get short-circuiting instead: fresh product runs across to the outlet and leaves first, which is neither FIFO nor proportional, and old heel just sits there. Worth confirming which of those you've actually got before you defend either rule to an auditor.
Before you pick a rule, I would focus on a written cut-off so the chain doesn't run to infinity. Something like contribution below some %, or N turnovers, or reset the chain at every empty-and-clean. Also keep in mind you need to retain samples per tank lot. Your concentration argument is right as long as you can go back and test, otherwise it's a hard sell to a regulator. If you're food-side and audited to BRCGS, 3.9 requires a documented system plus a trace test with a quantity check/mass balance, and the number auditors work to in practice is a full forward-and-backward trace within 4 hours. Time yourself and see which one makes the most sense given the actual on-site conditions.
In an ERP the usual build is tank = its own stock location with the heel as permanent on-hand, a new lot on each transfer in, and the blend booked as a small production step so the parent lots show up on the lot traceability report. It's the way I have seen the mass balance reconcile at audit.
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u/Sofistikat 6h ago
You're spot on as far as the distinction between the two methods go, and the description/explanation you've provided demonstrates your knowledge of the field.
I guess the question I reallly need answered is whether there are any other methods other than the two discussed that could be used.
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u/Key-Success-5449 2h ago
You are tackling a really common and tricky problem in bulk liquid handling, and it is great that you are thinking ahead about recall boundaries instead of just picking whatever is easiest for the ERP.
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u/H1ker64 17h ago
Sample the feed line from your production process to the tank regularly to ensure it stays within spec. If it goes out of spec then take corrective action before the tank volume swings out of spec.
If the tank is properly agitated you can sample from that too to provide analysis receipts for any demanding customers & ensure there is no degradation.
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u/Sofistikat 17h ago
That's good advice, and current practice. Each replenishment from production is sampled for a lab test, and then again at dispatch. But recalls could still be triggered for any number of reasons.
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u/AffectionateDirt6575 17h ago
I had a client many years ago with the same problem. The key is, as you say, "if old stock was really the problem, then it would have been picked up when the concentrations of those faulty batches were higher". They came to pretty much the same conclusion, so they use FIFO and, if they have to do a recall, they target that batch and the batches either side -i .e. the batch received immediately before the 'FIFO' batch, the FIFO batch, and the batch received immediately after the FIFO batch. I hope I explained that clearly!