<span style='color:brown'>There are several things about this you haven't mentioned. What is the diameter of the pipeline, what is the pressure, what is the age, etc. These will all bear some impact on the stigma, if any, that is attached to the property.
One way of measuring any real stigma can be ascertained by comparing lot sizes with selling prices. If you graph them out, you will find that lots with a pipeline are frequently close to 10% bigger than other lots in the neighborhood...and they sell for the same price, not at a premium. This should not influence the current valuation as this size differential is "built-in" to the current prices. Under different circumstances a larger sized lot would normally sell for a somewhat higher price. If this is a larger lot than it's neighbors that do not have the pipeline and it sells for the same price as its neighbor, then the stigma, such as it is, has already been incorporated.
Another concern deals with the easement itself and its proximity to the home. If this is a 30" pipeline, 20' is nowhere near enough distance from the house....such esements are 75'-150' wide. If the pipeline went in after the home was built, the entire property should have been taken. If it was built after the pipline was put in, then the home is non-conforming and any disaster (fire, tornado, etc) will require removal of that portion of the house. If the pipeline is an 8" or 6" line at less than 150 psi, then the 20' might be enough. Either way, I remember the Carlsbad explosion a few years ago and would not willingly live within the explosion zone, ever.
Other considerations is anode replacement, stray voltage (static electric energy developed by the anodic reaction of the soil to the pipe.....the reason you need zincs or some other anodic discharge medium.) potential.......it has not been proven, but stray voltage can also be created by high power lines crossing over the pipeline (the University of Wisconsin in Milwaukee is doing research now on the subject of stray voltage and the reduction in milk production it causes), a clear run for aircraft patrol of the pipeline, ground water depth (pipes filled with a light gas or petroleum can "float" to the surface over time, requiring re-excavation about a quarter to half a mile past each end of the floated pipe (depending on it's depth) to allow it to "sag" back into place.
Also you will need to verify that there are no trees or shrubs growing on the easement. A homeowner who violates the easement and allows permanent trees or shrubs to grow on an easement can be required to remove them at the homeowners expense....same thing includes fences.
All in all, pipleines are a problem and are not addressed properly in most reports I have seen....but then it takes more than a driveby and an opinion to develop a supportable value for the stigma.</span>