Hi Cyrus,
At high level, this is what I can think off right now [it could have better answers though...] -
a) If you are sure that you are going to inspect only the 'Gas Tanks", and NOT the gases stored in the tank, then you can potentially use Plant maintenance process. In such case, you can create inspection lots [type 14] against the equipment as 'Gas Tank' and do result recording for multiple MIC parameters for the tank [Length, diameter, SS quality, etc] as well as the % gases by volume for the overall sample taken or ppm. You can schedule a maintenance plan or manually create a PM order for 20 days for the equipment, where each such cases will create 1 inspection lots for 20 days and total 3 inspection lots in 2 months.
As this is a high level idea, you can speak to your PM team to see if this can be achievable.
b) Else, if you are trying to check only the 'Gases' stored in the tank, and NOT the 'Gas Tank' itself, then you can try to go via either of the options applicable for your business -
i) Recurring Inspection - Activate 09 inspection type for the Gas material "M", where you will have MIC's to calculate % of other gases by volume or ppm. You need to go through the pre-requisites, and manually update the dates, so that your recurring process works. Then schedule a batch job with a frequency for 20 days, with such a logic that if for one material M, already it previous inspection lot "Failed" inspection, then for that serial number, there is no new inspection lot created.
ii) Create a custom program with your business logic, that it should create manual inspection lots of type 89 for the material M, where % gases can be tested by volume. Run this program, so that it creates 3 inspection lots against the 20 days margin and difference dates. Create a follow-up action and add to a new "R1" UD code, so that if for the same serial number 1st inspection lot is reject - then it should CANCEL other two inspection lots created. If the 1st inspection lot is "A", but 2nd inspection lot is "R1", then it should CENCEL the 3rd inspection lot. As soon as a rejection happens, post the stock to "Blocked" stock and / or create return PO, via Follow-Up actions!!....
Thanks,
Arijit