Undergound Pipes Should Be Locked Behind Research

[Stopdropanddie]

I think it would be a good idea for undergound pipes to be locked behind research, just like underground belts. I think this for the same reason as with underground belts, so that you can research technology to be able to create more sophisticated setups. In the same vein as underground belts, underground pipes are not necessary for early setups. All in all, I think underground pipes should be locked behind a research node for 10 red science packs, perhaps with the name of "basic fluid handling" or something similar.

[FuryoftheStars]

Not sure I fully agree. Unlike regular belts, you can't pass through regular pipes. You need the undergrounds to not create a situation where you're cutting yourself off from something or forcing yourself to take the long way around. Oh, and due to fluid mechanics, underground pipes actually allow you to get the fluid further before needing a pump, which is also something that doesn't apply to belts.

[Stopdropanddie]

I see what you mean, but it still feels a bit wrong to have one undergound at the beginning of the game, but not the other.

[vangrunz]

Just add Underground Pipes to "Logistics" in Research Tree, and you're done. In such early phase you don't care about fluids at all, except water for low-level steam. Together with Tier 1 underground belts/splitters the cost of the Automation Science Pack should be increased no more than by 5.

Or, another suggestion:
Place it at Tier 2 "Fluid Handling", together with the Storage Tank. Again, more than 5 additional science packs of Tier 1 & 2 each should match balancing.

[shopt]

Like with all suggestions, I think the standard "how does this make factorio a better game to play" question applies here. "More realistic" != better.

In addition to what Fury said about ground pipes being impassable, you also can't mix fluids in pipes whereas you can mix items on belts. Lack of belt undergrounds and splitters can be worked around (it's not pretty, but possible). Lack of pipe undergrounds effectively turns every pipe into a wall that you have to walk around and route other fluids around too.