Regarding the glitch on AWBW in which Pipes are visible to every player during fog, this applies to ALL Pipe varieties. Any unit on a Pipe, or where a Pipe once was, can be seen by everyone. However, already broken seams (ones placed in map maker) have fog cover.
Pipe Seams have the same characteristics as Pipe, but they may be broken by units. Each has 99 hit points. Often, Pipe Seams are used as a gate to a front providing either an alternate route or access to bonus/key properties. Once broken, the Seam turns into a Broken Seam, which serves as a plains tile (Note: It will not turn into a Sea tile). When a Seam is broken, a Piperunner may not traverse it, but any other land/air unit may. For design purposes, a map revolving around a Pipe Seam is likely to be chokey, possibly resulting in stalemate.
Below is a list of the damage each unit does to a Pipe Seam. These values are not constant and may change with CO bonuses. Towers also affect this. Each Seam has 99 hit points.
Md. Tank: 45
Mega Tank: 115
Battle Copter: 20