I always make the pipe guys answer that question.
Will pooled liquid in their pipes cause any problems if there is a sag in the bridge?
How much can the joints "give" before breaking?

I just finished design of a 120' pipe bridge. The mechanical on the project wanted maximum 1/8" deflection. I told him that was impossible.

I'll echo ONCE20036, ask your pipe guys. There is a decent chance they will need to slope one or more pipes. On my bridge we ended up sloping it to provide drainage to a KO.

Piping is pretty resilient and a properly designed pipe run should be able to take L/240 for deflection.

Definitely ask the pipers. Generally the bigger the pipe is, the less deflection they can tolerate.

More often (from a piping perspective) is is a very important matter of WHERE the deflection is and HOW MUCH deflection (bending) is expected. Drain points (constant downward slopes to a very specific point, vent points or vapor protection requires constant upward slopes to a different point, sewage or slurries require specific max and min slopes to move the entrained solids to the end of the pipe, etc.

The pipe itself and contents are usually very predictable loads. (Surge and water hammer unpredictable but massive loads.) Expansion and contraction require specific large geometric bends and straights and anchors, but it is drains and vents and cargo capacities transfers that force slope limits on the supports. And a pipe bridge is just an expensive support, as far as a pipist cares..

Thanks to all for your input. Well noted.