Did not have time to try it out yet, but your mod description is convincing enough, which "tells" me I should use it the next time I play the game!

Always looking for some higher throughput pipes. But very often those mods are just introducing some sci-fi pipes, having ridiculous higher densities / flow rates in the same pipe cross-section. Not seems obeying the basic laws of fluid physics. Maybe some enormous energy to justify compressing the fluids (for the high pressure), but no such thing either. Thus I found them too cheaty to my playstyle.
Now you give us double width pipes/ducts, so four times in cross-section (thus also flow volumes). How reasonable they are! This is what we do to the oil and gas pipelines in the real life! I must thank you for doing this mod!

Now comes to my idea/suggestion:
Do you plan to add pipes/ducts of even larger widths? (Say up to width-4.)
A width-4 pipe/duct would have 16 times throughput of the vanilla pipe.
Be they as separate new entities, or some option settings to choose the width. Or else introduce as a separate mod?

This may be useful to one of my mod made some time ago, called Schall Machine Scaling. It has some scaled-up (both in physical size and capacity) versions of boilers, nuclear reactors, etc. The pipe connections are "scaled-up" accordingly. For example, my boiler +1 is size 6x4 with four times in water & fuel consumption, has pipe connections of width-2 on each end. And there are even +2, +3, +4, etc machines, which have pipe connections to width of 3, 4, 5, etc, respectively.
Your width-2 ducts come handy to such use, and would even be better if there are width-5 pipes/ducts.

PS: The game does not run well if an entity (say, 50x50) goes too large in graphics. It takes up too much memory, not healthy to FPS/UPS, or simply not load. Otherwise, I would have all my machines scaled-up in size quadratically rather than linearly, which violates "physics" a bit... Say, my oil refinery +4, which is equivalent to 256 vanilla oil refinery, should go 80x80(!) rather than current 25x25... This info is not relevant to you, but just saying I want to obey to laws of physics as much as possible, like what you have done in your mod. :-D

I really appreciated ur comment to my mod, above all from a respectable modder how u are :)

Anyway, for now I'm not plain to add bigger enitites, maybe some tool-entity if i found something of useful, because;

one problem with have bigger entities that must move fluids is that the fluid flow depend from their fullness, so bigger is the size, greater is the time that they need to be operative, and if the flow request is higher that max flow, could cause an underflow and be counterproductive.

I receive constantly feedback about this mod like: "flow is lower that vanilla pipe", "entities don't work", "i construct a long duct and at the end there isn't fluid"... and when I ask to each one to describe the problem in details, I point out the fact that players don't know how works Factorio fluid system, because isn't intuitive and is approximated, most of all, is designed to force players to use trains for transport fluid over long distance (100-150 tiles). For this, duct must be used in facility, not like trains...

In conclusion, I don't find useful introduce a bigger version.

Thanks for your quick response.
I haven't actually played the game these weeks, so I am not yet aware of the potential problems. But it seems those players lay out a pipe system MUCH beyond what they needed as some kind of reserves, and assuming a 5% filled pipe still "flow as a continuum fluid"... It is like asking a single water droplet will "automatically flow" inside a pipe, like our usual tap water streams...
It's not only about Factorio physics of fluid system, but as real world physics as well. One needs to fill the pipes upstream somehow, so there is enough fluid pressure from the "fullness", in order to flow downstream where the fluid pressure is lower.

Still, I want to convince you, since the machines in my mod can take really heavy water/steam flow. Vanilla boiler takes 60 fluid/s at max load. Each overtier is 4 times the previous... So boiler +3 is taking 3840 fluid/s at max load.
I have carefully tested all that, and found that the vanilla pipes are the bottlenecks preventing boiler +4 (15360 fluid/s) to work. There is no way to amass this amount of water into the 5 pipe connection points into it, with just vanilla pipes and pumps.

But I respect if you really don't want any bigger versions in this mod. Do you accept if implementing them (by you or by me, or anyone interested) as an extension mod?
It would be just like how I "scaled up" the vanilla machines in my above mentioned mod, but this time it is about scaling up your ducts. :-)

If u want do an addon u are free to do it, the sprites is scaled at 0.5 so at 1.0 shouldn't bad to look at, and theoretically if u make it doulbe, 4x4 block could have 64k of fluid, that is a monstrosity, so is enouth for ur pourpose. Also, if u need new graphic u must ask to Krastor that is the co-author that make the sprites.

I'm sorry for not be able to take ur request, but currently I'm busy to make Krastorio and SE compatible and improve Krastorio code, this will at least a month.

If u want do an addon u are free to do it, the sprites is scaled at 0.5 so at 1.0 shouldn't bad to look at, and theoretically if u make it doulbe, 4x4 block could have 64k of fluid, that is a monstrosity, so is enouth for ur pourpose. Also, if u need new graphic u must ask to Krastor that is the co-author that make the sprites.

I'm sorry for not be able to take ur request, but currently I'm busy to make Krastorio and SE compatible and improve Krastorio code, this will take at least a month.

Thank you! I will notify when such a new mod is ready.

Don't worry for the graphics scaled. I don't even bother to make any additional graphics for the 25x25 oil refinery +4 neither. Those interested in the Machine Scaling mod are in favour of better UPS anyway. I will simply use the original graphics, directly those from your mod in this case.
Krastorio is a big mod, and definitely worths a higher attention. So take your time. Wish you a productive modding!

PS: Just aware of the license. I have never work with GNU LGPLv3, so I am not familiar with that.
Not sure how "library" is defined in Factorio mod coding. Also not sure whether the new mod will counts as a "larger" work, so not needing to use the same license?
Currently, all my mods are using the custom license made by Bob (bobingabout) for his series of mods. Is it okay if I keep using that license?

Yeah u must cite the source and use same licence or another more limited