A pipe bridge is a specially constructed bridge that allows a pipeline to run over rivers, highway overpasses, deep ravines, or geologically or ecologically unstable or vulnerable land areas. The pipelines traversing these bridges may be to supply a town with water from a river or reservoir, or to irrigation stations on large farming plantations. Additionally, pipelines may carry effluent from mining operations to loading areas for trucking or railway transport. Sometimes they carry liquefied natural gas from the processing area of a plant to railway lines or harbors for loading upon tankers. There are sometimes pedestrian or maintenance pathways next to pipe bridges as well.
The design of a pipe bridge must take into account the weight of the pipes when carrying a full load and the effects of weather conditions on both the pipes themselves and the bridges that hold them. Engineers do materials testing of the materials that are used in pipe bridge construction, and structural and dynamic stress testing of the completed designs for the climate and weather patterns expected in the region where the bridge is to be constructed. Some designs create bridges that protect valued natural resources and leave as little footprint in a wilderness areas as possible. Whenever possible, suspension bridges are designed to carry pipelines above the ecosystems below; this often involves designs that are both practical and visually appealing.
Many suspension bridges over rivers or ravines are constructed on site and carefully built to withstand extreme weather and wind conditions. Bridges that are constructed out of steel and prestressed concrete are often built nearby in segments and then pieced together over abutments and pillared supports. One such bridge in South Africa was pieced together just off site. Then, the entire bridge, weighing 156.5 short tons (142 metric tons), was lowered into place using a heavy loading crane. After the completed bridge was fully applied over its support system, more than 441 short tons (400 metric tons) were added in concrete pedestrian pathway and hand railings.
Pipe bridges that transport water pipelines in northern countries must consider winter effects as well. Therefore, these bridges can be built that clad iron pipes in what are called mechanical pipe bridge crossings. These mechanical crossings include aluminum sheathing around the iron pipes, with a heated source inside that keeps the water at a constant temperature, regardless of how cold the weather. These insulated pipeline designs help ensure a town's water supplies are not jeopardized by the freezing of the pipelines.
