When the Alaskan Pipeline was constructed, valves were buried in the earth with only the controls above the surface. These valves have needed to be repaired as the pipeline has aged. Digging around the valves was a tricky process and something to be avoided in the future. 

So, when the pipeline authority began digging these up with more regularity, they needed a solution that didn't require contact with dirt; they devised valve vaults. There are many different corrosion-related problems that the owners took into consideration, especially extreme temperatures. Alaskan temperatures can exceed -100 F, however, the pipeline itself is a fairly constant 140 F (60 C). Meaning, water will condense on the pipeline, eventually filling the vaults with water. There are also a wide variety of pH levels in the surrounding soils. Rough handling of the vault was also a consideration; the coating on the vault needed to withstand transportation over a long distance. Hot-dip galvanizing holds up well in all three of these conditions and will protect the Alaskan Pipeline valves for decades to come.