Technical Articles
What is Wrong with the Pallet Storage Strategy in SAP EWM?
Introduction
The pallet storage strategy P is available both in EWM and LE-WM. Its key feature is that depending on a handling unit (or storage unit in case of LE-WM) type, a storage bin is dynamically divided into sub-bins (or sections):
Pallet Storage Strategy (source: SAP Help)
The number of bin sections depends on the type of a pallet being placed, for instance if a bin accommodates 3 euro pallets and 2 industrial pallets, the bin is divided into 3 sections upon the placement of an euro pallet into the empty bin and into 2 sections upon the placement of an industrial pallet.
The beauty of this approach is that bins are divided dynamically during placement. It is not needed to create separate bins for euro pallets and industrial ones.
SAP Help documentation:
SAP Help documentation of the strategy for EWM and LE-WM is very similar if not identical. Therefore the strategies must work the same in both systems.
Notice, that the documentation always uses a sequence of bin section numbers from left to right. In real life however, very often the first pallet is placed in the leftmost section, the second one in the rightmost section and the third one in the middle location. That reduces a risk of damages during storage.
Prompted by a question from Marek Kamiński I have checked how the strategy works in EWM and LE-WM.
I have run the same test case in both systems, i.e. placing of 3 handling / storage units with the same bin sectioning E D C B A.
I would expect the following placement results:
- the first handling/storage unit -> section E,
- the second handling/storage unit -> section D,
- the third handling/storage unit -> section C.
Additionally, the results in EWM and LE-WM would have to be the same as there are no differences in the strategy P behaviour in both systems.
Pallet Storage Strategy in SAP EWM
Bin sections (sub bins) in EWM
I have started with an inbound delivery with three handling units:
The Initial Inbound Delivery
Then, I have created the stock placement warehouse tasks for the handling units:
Placement with Strategy P in EWM
Notice, that the first task has been placed as expected into sub bin E. However the other two task have been placed into sections A, B, not into D and C as expected and as defined in the bin sections configuration.
Surprised by the odd result, I have rerun exactly the same test in LE-WM.
Pallet Storage Strategy in SAP LE-WM
Bin Sections in LE-WM
Placement with Strategy P in LE-WM
Notice, that LE-WM has placed the storage units exactly as expected and as defined in the bin sections configuration.
Technical Details
I just could not leave it like that and needed to get to the bottom of it. I have debugged the placement strategy in EWM, which is defined in the /SCWM/PUT_BIN_DET function group.
In my opinion the root cause of the issue is the empty bin buffer sorting logic implemented in the BIN_DETERMINATION_2 form routine – lines 140-158. The logic does not refer to the bin sectioning configuration whatsoever:
Empty Bins Buffer Sorting Logic
During the first warehouse task creation, the state of the buffer is as follows:
Empty Bins Buffer During the First Task Creation
Notice that the sub bin 0070-01-01/E is the first one in the buffer. Hence the first task goes to this sub bin, which is the expected result.
However, just before subsequent tasks are created the buffer is sorted and its state is as follows:
Empty Bins Buffer During Subsequent Tasks Creation
The way the buffer is sorted explains why the second and the third handling units are placed into bin sections A and B, instead of D and C.
It looks like the pallet storage strategy P does not respect bin sections configuration when sub bins are already created and sorts them as regular empty bins.
Conclusion
The tests have been conducted on S/4HANA 2022 FP01 system with embedded EWM. That is a quite recent release. I have also reviewed support notes, but to no avail.
Honestly, I am stunned. The pallet storage strategy P is one of the basic features of EWM. It must be commonly used by numerous customers. Have anyone not noticed that problem yet? Or am I missing something?
I would appreciate your comments and experience sharing with the pallet storage strategy P. Correct me if my conclusions are wrong.
Maybe the EWM product owner from SAP sheds some light on this?
Hello Dominik,
Thank you for a such great blog. I'm wondering how other people handle with sub-sectioning topic. I tested it in decentralized EWM 9.5 and the sequence was completely different than in customizing (I wanted to have 1/4/2/3 but I had 1/2/3/4.
I was testing it in WM as well and the sequence was correct there (according to sequence defined in customizing).
I'm curious what other people's experience have. I'm looking forward for feedback.
Best Regards,
Marek
Thank you!
Can you confirm that you observe the same behavior in EWM 9.5 as I have observed in S/4HANA embedded EWM?
Hello Dominik,
OK, I confirm, here is the example form EWM 9.5.
The first test:
Customizing:
And warehouse tasks sorted by confirmation time:
The second test with different logic (both don't work properly) - the behavior like in your test
customizing:
And WTs:
Thank you,
Best Regards,
Marek
Hi Dominik,
I had tested this subsequence scenario with two different HU types in S/4HANA 2021 system. Please check the configurations below if haven't
If I got it right, the idea is to use not 12345 sequence, but for example 15243 ( I had a use case 132). For 12345 sequence, Standard free bin sorting would work.
Daniil Mazurkevich How do you propose to use standard free bin sorting sequence for sub bins? The issue is not with how bins are sorted but with how sub bins resulting from strategy P are sorted.
my comment was to the sequence 12345 from Ömers test, in your aexample it is EDCBA, if it would be ABCDE you probably wont see any problem, just because system would sort it the same way, therefore it should not be tested with 12345, how Ömer Burak did it.
Daniil Mazurkevich Understood - thank you for comments
Hello Ömer,
Your configuration looks good but the question is what will happen if you set the sequence 1/3/2 in your system.
Best Regards,
Marek
hello again
It was an issue that I was wondering and working on before, I tested it again with 2 different address segmentation definitions.
The first is O/B/G made the storage as I listed,
first O then created B as the repository task
the second time I tried 3/5/2
It didn't follow the order I Assigned and created a warehouse task from smallest to largest.
Ömer Burak Gedik You need to use a bin division setting with more sub bins that 3, e.g. 5 to really see the problem.
In case of the bin division O, B, G:
Try with the bin division O, G, B.
Hi Former Member ,
while I agree that the behaviour you found questionable, your assumption "In real life however, very often the first pallet is placed in the leftmost section, the second one in the rightmost section and the third one in the middle location" is maybe simply not right or not used by that many customers (after questions I get in my classes, I never assume anything as "real life" ;-)).
And I guess no customer ever opened a ticket for this behaviour and the sorting was never questioned. The way it looks (for me as someone who can not develop) is that the first sorting is build on the creation of the bins by your customizing, after that it is simply numerically / alphanumerically). Of course the standard sorting sequences from CLSP can not be used. And yeah, so probably the sorting defined in the bin section definition in customizing should be continuously used.
Some of the EWM developers do read and answer questions here, but my recommendation would be to open a ticket for this issue so that the support can look into it.
Brgds
Juergen
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All the above is no official SAP statement.
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And it is EWM. NOT eWM - Duh!
And if your question includes the word "transfer order" - do NOT tag the question with Extended Warehouse Management!
Hi Juergen Pitz
Thank you for the comment and acknowledgement of the issue. As the statement:
"In real life however, very often the first pallet is placed in the leftmost section, the second one in the rightmost section and the third one in the middle location"
which you have commented comes from the blog, let me explain.
I have encountered this kind of placement sequences in real life scenarios. If you think about that, a sequence like that does reduce a risk of damages during the placement. However I have never had a chance to implement a sequence like that within pallet storage P strategy.
I suppose the pallet storage P strategy is not used that commonly after all. It is even less commonly used with storage sequences as in the blog. That is most probably the reason why the problem has not pop up yet.
Anyway I am going to open an OSS ticked as I am not hearing any reasonable explanation for this behavior of EWM.
Cheers
Dominik Tylczynski
I have finally managed to open a ticket about that issue: 464237 / 2023 Incorrect sequence of sub bins in pallet storage, strategy P
Hi,
Do let us know your further discussions on the OSS with SAP. Curious to know as to why this would be happening and the possible resolution for the same.
Regards,
Vatsal Bhanushali
Hi,
To give some inputs about "why bin sectionning is may be not used so often", we found a big limitiation when investigating this functionnality for the project I am working on : sub bins get the same sorting key as the main bin which to serious limitation in some business scenario.
In case of full pallet picking, no problem.
But in case of detail picking in high bins (or even ground picking), backward movement is generlly forbidden and having the same sort key for the full level is a problem : because it is physically impossible to pick on a 2400 mm live from any position. depending of the way the different levels of the same stack are sorted and depending of where you have to pick on each level, it is impossible to ensure that no backward movement will happen .
B.R.
Good point! Thank you!