You can look at the terrain to get an idea, but you can't always see what you are working with. Basically you never know. When they build pipelines, they often weld as many sections as possible together up on top, xray and paint, then walk the whole string in starting at one end and going to the other. As a single 40 foot stick the pipe is very ridgid, but weld several together and it's like a hose. So walking up to a random spot you never know what you got. Chit can kill you in a bunch of different ways.
Here's a video of the process, the laborer is doing what's called jeeping, which checks the integrity of the coating. Brave man touching the pipe while he was doing it, really good way to get lit up, pretty high voltage, kinda like a cattle prod. You can even see the roller slings. Here they are doing smallish pipe, so you can get away with using an excavator, on big pipe you absolutely need sidebooms.... man i miss pipeline.