Galvanized water supply pipes were the most common method of providing water to homes and inside homes from the early 1900’s until the early 1950’s. While there are a lot of factors that can contribute to how long these pipes will last, it is generally recognized that these pipes have a life expectancy of 40-50 years. By these guidelines there is likely none of this piping that is not past its expected life.
I have to say “likely” because I inspected a home 4 years ago where all of the original plumbing had been replaced with brand new galvanized piping----very unusual.
At the same time period that these supply pipes were being used, the same type of piping was used for drains as well. One should conclude that these pipes are also at the end of their expected life. When I find them I usually recommend replacement of both supply pipes and drain pipes for cost efficiency. Once the plumber is there why not have them replace both. Here is a picture of a drain line that has reached the end of its expected life. The stalactites of corrosion are where the pipe is leaking and re-sealing itself through a process called Auto-genic healing. This process will go on until the pipe can no longer seal itself and total failure will occur with much leaking/flooding being the result.
When your pipes look this bad on the outside it is a safe bet they look much worse on the inside.
PS, for those of you that are new to my blog (or for some other "unexplained" reason have never noticed)all pictures and smiley-face inserts (emoticons) (when I use them) have messages that show up when you point at them with your cursor.