[2.0.69] Underground pipe connections on machines can interfere with eachother beyond their max connection distance.

[oobanooba]

For my mod, I created a machine that uses underground pipe connections of a special "unpipable" connection category with a range of 1 instead of the regular fluid pipe connections. (to allow an implementation of unpipable fluids which require direct machine-to-machine transfer)

I constructed two machines next to each other, and they can transfer fluids as usual, until I placed a third machine several tiles away. This caused the two previously connected machines to become disconnected. Removing the third machine allows the first two to reconnect. This happens despite the third machine being placed beyond the underground pipe connection distance. It appears to me that there's no reason that this machine should be able to remotely break other machines' connections.

I noticed, in particular, that the distance at which this happens (10 tiles) seems to correspond to the default underground pipe distance.

Factorio 2025.10.25 - 21.18.27.03.mp4

(2.14 MiB) Downloaded 16 times

Factorio 2025.10.25 - 21.02.38.02.mp4

(7.24 MiB) Downloaded 12 times

[Techjar]

The bug aside, isn't using a different connection category the correct way to accomplish this? Just like how fusion plasma works in space age. It won't connect with base game pipes, and you simply don't create a pipe entity that does.

[robot256]

For my mod, I created a machine that uses underground pipe connections of a special "unpipable" connection category with a range of 1 instead of the regular fluid pipe connections. (to allow an implementation of unpipable fluids which require direct machine-to-machine transfer)

Can you attach the test mod and save file that reproduces the issue?

The bug aside, isn't using a different connection category the correct way to accomplish this? Just like how fusion plasma works in space age. It won't connect with base game pipes, and you simply don't create a pipe entity that does.

Yes it is, and shouldn't affect this bug at all since all the machine connections involved have the same connection category.

[boskid]

Uh, i see where the fault in the pipe connection logic is.

This bug is caused by incorrect handling of underground pipe connections when some of them are set to flow_direction = "input" or flow_direction = "output". Since two underground connections of type "output" are unable to connect to each other, in the video with 2 thrusters and 2 assemblers, one assembler does not see the other one (due to incorrect check that uses flow direction) and so it reaches thruster and asks it to disconnect because by reaching it in the backward search it must have been connected to an underground connection that spans under the assembler (which is not true because search simply failed to noticed the other assembler).

[boskid]

Thanks for the report. issue is now fixed for the next release.

[oobanooba]

Thanks for the report. issue is now fixed for the next release.

you are a legend, thank you!

[Techjar]

Yes it is, and shouldn't affect this bug at all since all the machine connections involved have the same connection category.

Yeah, I just thought it's weird to be using underground connections on an assembler to force direct connection.