During a period in the early 1970's when Russia began buying US grain in vast amounts account crop failures throughout Russia and Ukraine, I was a supervisor at B&O's Locust Point yard which serviced the Indiana Grain elevator and export pier, during the month of February that year there were 61 derailments in the yard ranging from one pair of wheels to 15 or more cars during the 28 days of that month. The yard had been built early in the 20th Century with 90 and 100 pound rail - which by the 1970's had far outlived it economical and mechanical life span. 65 and 100 car unit trains of 100 net ton covered hoppers took a terrible toll on all the then current infrastructure. Starting that summer B&O (Chessie System) undertook a major refurbishment of the yard installing new switches and crossovers as well as installing relay 122 pound welded rail in all the areas that were used to support grain activities. Hard to realize that all that happened 50 years ago.
In 2011 KCS replaced 90 pound rail (rolled in 1921) on the 65 mile Gulfport (MS) branch to Hattiesburg with 115 pound CWR. I was told the 90 pound rail would then replace the 75 pound Gulfport yard rail installed when the line was built in 1912. By 2011, KCS was running 4-axle GP's with loaded covered hoppers and 40-foot tanks. Occasionally 6-axle CSX rerouted manifests and double-stacks would show up. I'm not in a position to know of any derailments, but reading this thread, I'm sure there must have been a few in the yard before 2011. Thanks DJ and mm16 for an interesting thread.
Fully creosoted wood ties have a nominal life expectancy of approximately 30 years. Locust Point, in addition to having rail that was installed near the start of the 20th Century also seemed to have most of the original ties that the rail had been installed upon. Ties that don't securely hold spikes to hold the rail and tie plates in place are a adjunct cause in numerous derailments. The conical shape of wheel treads as well as the crowned nature of the top of the rail generate a twisting force upon the rail attempting to force the rail to the outside of the gauge line - if the ties don't hold the spikes securely, the rail then turns over from the forces being placed against it. Each element of the track structure works with all the other elements to keep the track structure performing its intended purpose without failure. Derailments will find the weakest of those elements.
